Added Test environment.

1 files changed, 6368 insertions, 0 deletions

diff --git a/test/ruby/pleac.in.rb b/test/ruby/pleac.in.rb
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+# -*- ruby -*-
+
+# Local variables:
+#  indent-tabs-mode: nil
+#  ruby-indent-level: 4
+# End:
+
+# @@PLEAC@@_NAME
+# @@SKIP@@ Ruby
+
+# @@PLEAC@@_WEB
+# @@SKIP@@ http://www.ruby-lang.org
+
+
+# @@PLEAC@@_1.0
+string = '\n'                     # two characters, \ and an n
+string = 'Jon \'Maddog\' Orwant'  # literal single quotes
+
+string = "\n"                     # a "newline" character
+string = "Jon \"Maddog\" Orwant"  # literal double quotes
+
+string = %q/Jon 'Maddog' Orwant/  # literal single quotes
+
+string = %q[Jon 'Maddog' Orwant]  # literal single quotes
+string = %q{Jon 'Maddog' Orwant}  # literal single quotes
+string = %q(Jon 'Maddog' Orwant)  # literal single quotes
+string = %q<Jon 'Maddog' Orwant>  # literal single quotes
+
+a = <<"EOF"
+This is a multiline here document
+terminated by EOF on a line by itself
+EOF
+
+
+# @@PLEAC@@_1.1
+value = string[offset,count]
+value = string[offset..-1]
+
+string[offset,count] = newstring
+string[offset..-1]   = newtail
+
+# in Ruby we can also specify intervals by their two offsets
+value = string[offset..offs2]
+string[offset..offs2] = newstring
+
+leading, s1, s2, trailing = data.unpack("A5 x3 A8 A8 A*")
+
+fivers = string.unpack("A5" * (string.length/5))
+
+chars = string.unpack("A1" * string.length)
+
+string = "This is what you have"
+#        +012345678901234567890  Indexing forwards  (left to right)
+#         109876543210987654321- Indexing backwards (right to left)
+#          note that 0 means 10 or 20, etc. above
+
+first  = string[0, 1]       # "T"
+start  = string[5, 2]       # "is"
+rest   = string[13..-1]     # "you have"
+last   = string[-1, 1]      # "e"
+end_   = string[-4..-1]     # "have"
+piece  = string[-8, 3]      # "you"
+
+string[5, 2] = "wasn't"     # change "is" to "wasn't"
+string[-12..-1] = "ondrous" # "This wasn't wondrous"
+string[0, 1] = ""           # delete first character
+string[-10..-1]  = ""       # delete last 10 characters
+
+if string[-10..-1] =~ /pattern/
+    puts "Pattern matches in last 10 characters"
+end
+
+string[0, 5].gsub!(/is/, 'at')
+
+a = "make a hat"
+a[0, 1], a[-1, 1] = a[-1, 1], a[0, 1]
+
+a = "To be or not to be"
+b = a.unpack("x6 A6")
+
+b, c = a.unpack("x6 A2 X5 A2")
+puts "#{b}\n#{c}\n"
+
+def cut2fmt(*args)
+    template = ''
+    lastpos  = 1
+    for place in args
+        template += "A" + (place - lastpos).to_s + " "
+        lastpos   = place
+    end
+    template += "A*"
+    return template
+end
+
+fmt = cut2fmt(8, 14, 20, 26, 30)
+
+
+# @@PLEAC@@_1.2
+# careful! "b is true" doesn't mean "b != 0" (0 is true in Ruby)
+# thus no problem of "defined" later since only nil is false
+# the following sets to `c' if `b' is nil or false
+a = b || c
+
+# if you need Perl's behaviour (setting to `c' if `b' is 0) the most
+# effective way is to use Numeric#nonzero? (thanks to Dave Thomas!)
+a = b.nonzero? || c
+
+# you will still want to use defined? in order to test
+# for scope existence of a given object
+a = defined?(b) ? b : c
+
+dir = ARGV.shift || "/tmp"
+
+
+# @@PLEAC@@_1.3
+v1, v2 = v2, v1
+
+alpha, beta, production = %w(January March August)
+alpha, beta, production = beta, production, alpha
+
+
+# @@PLEAC@@_1.4
+num = char[0]
+char = num.chr
+
+# Ruby also supports having a char from character constant
+num = ?r
+
+char = sprintf("%c", num)
+printf("Number %d is character %c\n", num, num)
+
+ascii = string.unpack("C*")
+string = ascii.pack("C*")
+
+hal = "HAL"
+ascii = hal.unpack("C*")
+# We can't use Array#each since we can't mutate a Fixnum
+ascii.collect! { |i|
+    i + 1                         # add one to each ASCII value
+}                
+ibm = ascii.pack("C*")
+puts ibm
+
+
+# @@PLEAC@@_1.5
+array = string.split('')
+
+array = string.unpack("C*")
+
+string.scan(/./) { |b|
+    # do something with b
+}
+
+string = "an apple a day"
+print "unique chars are: ", string.split('').uniq.sort, "\n"
+
+sum = 0
+for ascval in string.unpack("C*") # or use Array#each for a pure OO style :)
+    sum += ascval
+end
+puts "sum is #{sum & 0xffffffff}" # since Ruby will go Bignum if necessary
+
+# @@INCLUDE@@ include/ruby/slowcat.rb
+
+
+# @@PLEAC@@_1.6
+revbytes = string.reverse
+
+revwords = string.split(" ").reverse.join(" ")
+
+revwords = string.split(/(\s+)/).reverse.join
+
+# using the fact that IO is Enumerable, you can directly "select" it
+long_palindromes = File.open("/usr/share/dict/words").
+    select { |w| w.chomp!; w.reverse == w && w.length > 5 }
+
+
+# @@PLEAC@@_1.7
+while string.sub!("\t+") { ' ' * ($&.length * 8 - $`.length % 8) }
+end
+
+
+# @@PLEAC@@_1.8
+'You owe #{debt} to me'.gsub(/\#{(\w+)}/) { eval($1) }
+
+rows, cols = 24, 80
+text = %q(I am #{rows} high and #{cols} long)
+text.gsub!(/\#{(\w+)}/) { eval("#{$1}") }
+puts text
+
+'I am 17 years old'.gsub(/\d+/) { 2 * $&.to_i }
+
+
+# @@PLEAC@@_1.9
+e = "bo peep".upcase
+e.downcase!
+e.capitalize!
+
+"thIS is a loNG liNE".gsub!(/\w+/) { $&.capitalize }
+
+
+# @@PLEAC@@_1.10
+"I have #{n+1} guanacos."
+print "I have ", n+1, " guanacos."
+
+
+# @@PLEAC@@_1.11
+var = <<'EOF'.gsub(/^\s+/, '')
+    your text
+    goes here
+EOF
+
+
+# @@PLEAC@@_1.12
+string = "Folding and splicing is the work of an editor,\n"+
+    "not a mere collection of silicon\n"+ 
+    "and\n"+
+    "mobile electrons!"
+
+def wrap(str, max_size)
+    all = []
+    line = ''
+    for l in str.split
+        if (line+l).length >= max_size
+            all.push(line)
+            line = ''
+        end
+        line += line == '' ? l : ' ' + l
+    end
+    all.push(line).join("\n")
+end
+
+print wrap(string, 20)
+#=> Folding and 
+#=> splicing is the 
+#=> work of an editor, 
+#=> not a mere 
+#=> collection of 
+#=> silicon and mobile 
+#=> electrons!
+
+
+# @@PLEAC@@_1.13
+string = %q(Mom said, "Don't do that.")
+string.gsub(/['"]/) { '\\'+$& }
+string.gsub(/['"]/, '\&\&')
+string.gsub(/[^A-Z]/) { '\\'+$& }
+"is a test!".gsub(/\W/) { '\\'+$& }  # no function like quotemeta?
+
+
+# @@PLEAC@@_1.14
+string.strip!
+
+
+# @@PLEAC@@_1.15
+def parse_csv(text)
+    new = text.scan(/"([^\"\\]*(?:\\.[^\"\\]*)*)",?|([^,]+),?|,/)
+    new << nil if text[-1] == ?,
+    new.flatten.compact
+end  
+
+line = %q<XYZZY,"","O'Reilly, Inc","Wall, Larry","a \"glug\" bit,",5,"Error, Core Dumped">
+fields = parse_csv(line)
+fields.each_with_index { |v,i|
+    print "#{i} : #{v}\n";
+}
+
+
+# @@PLEAC@@_1.16
+# Use the soundex.rb Library from Michael Neumann.
+# http://www.s-direktnet.de/homepages/neumann/rb_prgs/Soundex.rb
+require 'Soundex'
+
+code = Text::Soundex.soundex(string)
+codes = Text::Soundex.soundex(array)
+
+# substitution function for getpwent():
+# returns an array of user entries,
+# each entry contains the username and the full name
+def login_names
+    result = []
+    File.open("/etc/passwd") { |file|
+        file.each_line { |line|
+            next if line.match(/^#/)
+            cols = line.split(":")
+            result.push([cols[0], cols[4]])
+        }
+    }
+    result
+end
+
+puts "Lookup user: "
+user = STDIN.gets
+user.chomp!
+exit unless user
+name_code = Text::Soundex.soundex(user)
+
+splitter = Regexp.new('(\w+)[^,]*\b(\w+)')
+for username, fullname in login_names do
+    firstname, lastname = splitter.match(fullname)[1,2]
+    if name_code == Text::Soundex.soundex(username)
+        || name_code == Text::Soundex.soundex(firstname)
+        || name_code == Text::Soundex.soundex(lastname)
+    then
+        puts "#{username}: #{firstname} #{lastname}"
+    end
+end
+
+
+# @@PLEAC@@_1.17
+# @@INCLUDE@@ include/ruby/fixstyle.rb
+
+
+# @@PLEAC@@_1.18
+# @@INCLUDE@@ include/ruby/psgrep.rb
+
+
+# @@PLEAC@@_2.1
+# Matz tells that you can use Integer() for strict checked conversion.
+Integer("abc")
+#=> `Integer': invalid value for Integer: "abc" (ArgumentError)
+Integer("567")
+#=> 567
+
+# You may use Float() for floating point stuff
+Integer("56.7")
+#=> `Integer': invalid value for Integer: "56.7" (ArgumentError)
+Float("56.7")
+#=> 56.7
+
+# You may also use a regexp for that
+if string =~ /^[+-]?\d+$/
+    p 'is an integer'
+else
+    p 'is not'
+end
+
+if string =~ /^-?(?:\d+(?:\.\d*)?|\.\d+)$/
+    p 'is a decimal number'
+else
+    p 'is not'
+end
+
+
+# @@PLEAC@@_2.2
+# equal(num1, num2, accuracy) : returns true if num1 and num2 are
+#   equal to accuracy number of decimal places
+def equal(i, j, a)
+    sprintf("%.#{a}g", i) == sprintf("%.#{a}g", j)
+end
+
+wage = 536                        # $5.36/hour
+week = 40 * wage                  # $214.40
+printf("One week's wage is: \$%.2f\n", week/100.0)
+
+
+# @@PLEAC@@_2.3
+num.round                         # rounds to integer
+
+a = 0.255
+b = sprintf("%.2f", a)
+print  "Unrounded: #{a}\nRounded: #{b}\n"
+printf "Unrounded: #{a}\nRounded: %.2f\n", a
+
+print "number\tint\tfloor\tceil\n"
+a = [ 3.3 , 3.5 , 3.7, -3.3 ]
+for n in a
+    printf("% .1f\t% .1f\t% .1f\t% .1f\n",  # at least I don't fake my output :)
+           n, n.to_i, n.floor, n.ceil)
+end
+
+
+# @@PLEAC@@_2.4
+def dec2bin(n)
+    [n].pack("N").unpack("B32")[0].sub(/^0+(?=\d)/, '')
+end
+
+def bin2dec(n)
+    [("0"*32+n.to_s)[-32..-1]].pack("B32").unpack("N")[0]
+end
+
+
+# @@PLEAC@@_2.5
+for i in x .. y
+    # i is set to every integer from x to y, inclusive
+end
+
+x.step(y,7) { |i|
+    # i is set to every integer from x to y, stepsize = 7
+}
+
+print "Infancy is: "
+(0..2).each { |i|
+    print i, " "
+}
+print "\n"
+
+
+# @@PLEAC@@_2.6
+# We can add conversion methods to the Integer class,
+# this makes a roman number just a representation for normal numbers.
+class Integer
+    
+    @@romanlist = [["M", 1000],
+                   ["CM", 900],
+                   ["D",  500],
+                   ["CD", 400],
+                   ["C",  100],
+                   ["XC",  90],
+                   ["L",   50],
+                   ["XL",  40],
+                   ["X",   10],
+                   ["IX",   9],
+                   ["V",    5],
+                   ["IV",   4],
+                   ["I",    1]]
+    
+    def to_roman
+        remains = self
+        roman = ""
+        for sym, num in @@romanlist
+            while remains >= num
+                remains -= num
+                roman << sym
+            end
+        end
+        roman
+    end
+    
+    def Integer.from_roman(roman)
+        ustr = roman.upcase
+        sum = 0
+        for entry in @@romanlist
+            sym, num = entry[0], entry[1]
+            while sym == ustr[0, sym.length]
+                sum += num
+                ustr.slice!(0, sym.length)
+            end
+        end
+        sum
+    end
+    
+end
+
+
+roman_fifteen = 15.to_roman
+puts "Roman for fifteen is #{roman_fifteen}"
+i = Integer.from_roman(roman_fifteen)
+puts "Converted back, #{roman_fifteen} is #{i}"
+
+# check
+for i in (1..3900)
+    r = i.to_roman
+    j = Integer.from_roman(r)
+    if i != j
+        puts "error: #{i} : #{r} - #{j}"
+    end
+end
+
+
+# @@PLEAC@@_2.7
+random = rand(y-x+1)+x
+
+chars = ["A".."Z","a".."z","0".."9"].collect { |r| r.to_a }.join + %q(!@$%^&*)
+password = (1..8).collect { chars[rand(chars.size)] }.pack("C*")
+
+
+# @@PLEAC@@_2.8
+srand        # uses a combination of the time, the process id, and a sequence number
+srand(val)   # for repeatable behaviour
+
+
+# @@PLEAC@@_2.9
+# from the randomr lib: 
+# http://raa.ruby-lang.org/project/randomr/
+----> http://raa.ruby-lang.org/project/randomr/
+
+require 'random/mersenne_twister'
+mers = Random::MersenneTwister.new 123456789
+puts mers.rand(0)    # 0.550321932544541
+puts mers.rand(10)   # 2
+
+# using online sources of random data via the realrand package:
+# http://raa.ruby-lang.org/project/realrand/
+# **Note**
+# The following online services are used in this package:
+#   http://www.random.org - source: atmospheric noise 
+#   http://www.fourmilab.ch/hotbits - source: radioactive decay timings
+#   http://random.hd.org - source: entropy from local and network noise
+# Please visit the sites and respect the rules of each service.
+
+require 'random/online'
+
+generator1 = Random::RandomOrg.new
+puts generator1.randbyte(5).join(",")
+puts generator1.randnum(10, 1, 6).join(",")  # Roll dice 10 times.
+
+generator2 = Random::FourmiLab.new
+puts generator2.randbyte(5).join(",")
+# randnum is not supported.
+
+generator3 = Random::EntropyPool.new
+puts generator3.randbyte(5).join(",")
+# randnum is not supported.
+
+
+# @@PLEAC@@_2.10
+def gaussian_rand
+    begin
+        u1 = 2 * rand() - 1
+        u2 = 2 * rand() - 1
+        w = u1*u1 + u2*u2
+    end while (w >= 1)
+    w = Math.sqrt((-2*Math.log(w))/w)
+    [ u2*w, u1*w ]
+end
+
+mean = 25
+sdev = 2
+salary = gaussian_rand[0] * sdev + mean
+printf("You have been hired at \$%.2f\n", salary)
+
+
+# @@PLEAC@@_2.11
+def deg2rad(d)
+    (d/180.0)*Math::PI
+end
+
+def rad2deg(r)
+    (r/Math::PI)*180
+end
+
+
+# @@PLEAC@@_2.12
+sin_val = Math.sin(angle)
+cos_val = Math.cos(angle)
+tan_val = Math.tan(angle)
+
+# AFAIK Ruby's Math module doesn't provide acos/asin
+# While we're at it, let's also define missing hyperbolic functions
+module Math
+    def Math.asin(x)
+        atan2(x, sqrt(1 - x**2))
+    end
+    def Math.acos(x)
+        atan2(sqrt(1 - x**2), x)
+    end
+    def Math.atan(x)
+        atan2(x, 1)
+    end
+    def Math.sinh(x)
+        (exp(x) - exp(-x)) / 2
+    end
+    def Math.cosh(x)
+        (exp(x) + exp(-x)) / 2
+    end
+    def Math.tanh(x)
+        sinh(x) / cosh(x)
+    end
+end
+
+# The support for Complex numbers is not built-in
+y = Math.acos(3.7)
+#=> in `sqrt': square root for negative number (ArgumentError)
+
+# There is an implementation of Complex numbers in 'complex.rb' in current
+# Ruby distro, but it doesn't support atan2 with complex args, so it doesn't
+# solve this problem.
+
+
+# @@PLEAC@@_2.13
+log_e = Math.log(val)
+log_10 = Math.log10(val)
+
+def log_base(base, val)
+    Math.log(val)/Math.log(base)
+end
+
+answer = log_base(10, 10_000)
+puts "log10(10,000) = #{answer}"
+
+
+# @@PLEAC@@_2.14
+require 'matrix.rb'
+
+a = Matrix[[3, 2, 3], [5, 9, 8]]
+b = Matrix[[4, 7], [9, 3], [8, 1]]
+c = a * b
+
+a.row_size
+a.column_size
+
+c.det
+a.transpose
+
+
+# @@PLEAC@@_2.15
+require 'complex.rb'
+require 'rational.rb'
+
+a = Complex(3, 5)              # 3 + 5i
+b = Complex(2, -2)             # 2 - 2i
+puts "c = #{a*b}"
+
+c = a * b
+d = 3 + 4*Complex::I
+
+printf "sqrt(#{d}) = %s\n", Math.sqrt(d)
+
+
+# @@PLEAC@@_2.16
+number = hexadecimal.hex
+number = octal.oct
+
+print "Gimme a number in decimal, octal, or hex: "
+num = gets.chomp
+exit unless defined?(num)
+num = num.oct if num =~ /^0/  # does both oct and hex  
+printf "%d %x %o\n", num, num, num
+
+print "Enter file permission in octal: "
+permissions = gets.chomp
+raise "Exiting ...\n" unless defined?(permissions)
+puts "The decimal value is #{permissions.oct}"
+
+
+# @@PLEAC@@_2.17
+def commify(n)
+    n.to_s =~ /([^\.]*)(\..*)?/
+    int, dec = $1.reverse, $2 ? $2 : ""
+    while int.gsub!(/(,|\.|^)(\d{3})(\d)/, '\1\2,\3')
+    end
+    int.reverse + dec
+end
+
+
+# @@PLEAC@@_2.18
+printf "It took %d hour%s\n", time, time == 1 ? "" : "s"
+
+# dunno if an equivalent to Lingua::EN::Inflect exists...
+
+
+# @@PLEAC@@_2.19
+#-----------------------------
+#!/usr/bin/ruby
+# bigfact - calculating prime factors
+def factorize(orig)
+    factors = {}
+    factors.default = 0     # return 0 instead nil if key not found in hash
+    n = orig
+    i = 2
+    sqi = 4                 # square of i
+    while sqi <= n do
+        while n.modulo(i) == 0 do
+            n /= i
+            factors[i] += 1
+            # puts "Found factor #{i}"
+        end
+        # we take advantage of the fact that (i +1)**2 = i**2 + 2*i +1
+        sqi += 2 * i + 1
+        i += 1
+    end
+    
+    if (n != 1) && (n != orig)
+        factors[n] += 1
+    end
+    factors
+end
+
+def printfactorhash(orig, factorcount)
+    print format("%-10d ", orig)
+    if factorcount.length == 0
+        print "PRIME"
+    else
+        # sorts after number, because the hash keys are numbers
+        factorcount.sort.each { |factor,exponent|
+            print factor
+            if exponent > 1
+                print "**", exponent
+            end
+            print " "
+        }
+    end
+    puts
+end
+
+for arg in ARGV
+    n = arg.to_i
+    mfactors = factorize(n)
+    printfactorhash(n, mfactors)
+end
+#-----------------------------
+
+
+# @@PLEAC@@_3.0
+puts Time.now
+
+print "Today is day ", Time.now.yday, " of the current year.\n"
+print "Today is day ", Time.now.day, " of the current month.\n"
+
+
+# @@PLEAC@@_3.1
+day, month, year = Time.now.day, Time.now.month, Time.now.year
+# or
+day, month, year = Time.now.to_a[3..5]
+
+tl = Time.now.localtime
+printf("The current date is %04d %02d %02d\n", tl.year, tl.month, tl.day)
+
+Time.now.localtime.strftime("%Y-%m-%d")
+
+
+# @@PLEAC@@_3.2
+Time.local(year, month, day, hour, minute, second).tv_sec
+Time.gm(year, month, day, hour, minute, second).tv_sec
+
+
+# @@PLEAC@@_3.3
+sec, min, hour, day, month, year, wday, yday, isdst, zone = Time.at(epoch_secs).to_a
+
+
+# @@PLEAC@@_3.4
+when_ = now + difference         # now -> Time ; difference -> Numeric (delta in seconds)
+then_ = now - difference
+
+
+# @@PLEAC@@_3.5
+bree = 361535725
+nat  =  96201950
+
+difference = bree - nat
+puts "There were #{difference} seconds between Nat and Bree"
+
+seconds    =  difference % 60
+difference = (difference - seconds) / 60
+minutes    =  difference % 60
+difference = (difference - minutes) / 60
+hours      =  difference % 24
+difference = (difference - hours)   / 24
+days       =  difference % 7
+weeks      = (difference - days)    /  7
+
+puts "(#{weeks} weeks, #{days} days, #{hours}:#{minutes}:#{seconds})"
+
+
+# @@PLEAC@@_3.6
+monthday, weekday, yearday = date.mday, date.wday, date.yday
+
+# AFAIK the week number is not just a division since week boundaries are on sundays
+weeknum = d.strftime("%U").to_i + 1
+
+year  = 1981
+month = "jun"                     # or `6' if you want to emulate a broken language
+day   = 16
+t = Time.mktime(year, month, day)
+print "#{month}/#{day}/#{year} was a ", t.strftime("%A"), "\n"
+
+
+# @@PLEAC@@_3.7
+yyyy, mm, dd = $1, $2, $3 if "1998-06-25" =~ /(\d+)-(\d+)-(\d+)/
+
+epoch_seconds = Time.mktime(yyyy, mm, dd).tv_sec
+
+# dunno an equivalent to Date::Manip#ParseDate
+
+
+# @@PLEAC@@_3.8
+string = Time.at(epoch_secs)
+Time.at(1234567890).gmtime        # gives: Fri Feb 13 23:31:30 UTC 2009
+
+time = Time.mktime(1973, "jan", 18, 3, 45, 50)
+print "In localtime it gives: ", time.localtime, "\n"
+
+
+# @@PLEAC@@_3.9
+# Ruby provides micro-seconds in Time object
+Time.now.usec
+
+# Ruby gives the seconds in floating format when substracting two Time objects
+before = Time.now
+line = gets
+elapsed = Time.now - before
+puts "You took #{elapsed} seconds."
+
+# On my Celeron-400 with Linux-2.2.19-14mdk, average for three execs are:
+#   This Ruby version:       average 0.00321 sec
+#   Cookbook's Perl version: average 0.00981 sec
+size = 500
+number_of_times = 100
+total_time = 0
+number_of_times.times {
+    # populate array
+    array = []
+    size.times { array << rand }
+    # sort it
+    begin_ = Time.now
+    array.sort!
+    time = Time.now - begin_
+    total_time += time
+}
+printf "On average, sorting %d random numbers takes %.5f seconds\n",
+    size, (total_time/Float(number_of_times))
+
+
+# @@PLEAC@@_3.10
+sleep(0.005)                      # Ruby is definitely not as broken as Perl :)
+# (may be interrupted by sending the process a SIGALRM)
+
+
+# @@PLEAC@@_3.11
+#!/usr/bin/ruby -w
+# hopdelta - feed mail header, produce lines
+#            showing delay at each hop.
+require 'time'
+class MailHopDelta
+
+    def initialize(mail)
+        @head = mail.gsub(/\n\s+/,' ')
+        @topline = %w-Sender Recipient Time Delta-
+        @start_from = mail.match(/^From.*\@([^\s>]*)/)[1]
+        @date = Time.parse(mail.match(/^Date:\s+(.*)/)[1])
+    end
+
+    def out(line)
+         "%-20.20s %-20.20s %-20.20s  %s" % line
+    end
+
+    def hop_date(day)
+        day.strftime("%I:%M:%S %Y/%m/%d")
+    end
+
+    def puts_hops
+        puts out(@topline) 
+        puts out(['Start', @start_from, hop_date(@date),''])
+        @head.split(/\n/).reverse.grep(/^Received:/).each do |hop|
+            hop.gsub!(/\bon (.*?) (id.*)/,'; \1')
+            whence = hop.match(/;\s+(.*)$/)[1]
+            unless whence
+                warn "Bad received line: #{hop}"
+                next
+            end
+            from = $+ if hop =~ /from\s+(\S+)|\((.*?)\)/
+            by   = $1 if hop =~ /by\s+(\S+\.\S+)/
+            next unless now = Time.parse(whence).localtime
+            delta = now - @date
+            puts out([from, by, hop_date(now), hop_time(delta)])
+            @date = now
+        end
+    end
+
+    def hop_time(secs)
+        sign = secs < 0 ? -1 : 1
+        days, secs = secs.abs.divmod(60 * 60 * 24)
+        hours,secs = secs.abs.divmod(60 * 60)
+        mins, secs = secs.abs.divmod(60)
+        rtn =  "%3ds" % [secs  * sign]
+        rtn << "%3dm" % [mins  * sign] if mins  != 0
+        rtn << "%3dh" % [hours * sign] if hours != 0
+        rtn << "%3dd" % [days  * sign] if days  != 0 
+        rtn
+    end
+end
+
+$/ = ""
+mail = MailHopDelta.new(ARGF.gets).puts_hops
+
+
+# @@PLEAC@@_4.0
+single_level = [ "this", "that", "the", "other" ]
+
+# Ruby directly supports nested arrays
+double_level = [ "this", "that", [ "the", "other" ] ]
+still_single_level = [ "this", "that", [ "the", "other" ] ].flatten
+
+
+# @@PLEAC@@_4.1
+a = [ "quick", "brown", "fox" ]
+a = %w(Why are you teasing me?)
+
+lines = <<"END_OF_HERE_DOC".gsub(/^\s*(.+)/, '\1')
+    The boy stood on the burning deck,
+    It was as hot as glass.
+END_OF_HERE_DOC
+
+bigarray = IO.readlines("mydatafile").collect { |l| l.chomp }
+
+name = "Gandalf"
+banner = %Q(Speak, #{name}, and welcome!)
+
+host_info  = `host #{his_host}`
+
+%x(ps #{$$})
+
+banner = 'Costs only $4.95'.split(' ')
+
+rax = %w! ( ) < > { } [ ] !
+
+
+# @@PLEAC@@_4.2
+def commify_series(arr)
+    return '' if not arr
+    case arr.size
+        when 0 then ''
+        when 1 then arr[0]
+        when 2 then arr.join(' and ')
+        else arr[0..-2].join(', ') + ', and ' + arr[-1]
+    end
+end
+
+array = [ "red", "yellow", "green" ]
+
+print "I have ", array, " marbles\n"
+# -> I have redyellowgreen marbles
+
+# But unlike Perl:
+print "I have #{array} marbles\n"
+# -> I have redyellowgreen marbles
+# So, needs:
+print "I have #{array.join(' ')} marbles\n"
+# -> I have red yellow green marbles
+
+#!/usr/bin/ruby
+# communify_series - show proper comma insertion in list output
+
+def commify_series(arr)
+    return '' if not arr
+    sepchar = arr.find { |p| p =~ /,/ } ? '; ' : ', '
+    case arr.size
+        when 0 then ''
+        when 1 then arr[0]
+        when 2 then arr.join(' and ')
+        else arr[0..-2].join(sepchar) + sepchar + 'and ' + arr[-1]
+    end
+end
+
+lists = [
+    [ 'just one thing' ],
+    %w(Mutt Jeff),
+    %w(Peter Paul Mary),
+    [ 'To our parents', 'Mother Theresa', 'God' ],
+    [ 'pastrami', 'ham and cheese', 'peanut butter and jelly', 'tuna' ],
+    [ 'recycle tired, old phrases', 'ponder big, happy thoughts' ],
+    [ 'recycle tired, old phrases',
+      'ponder big, happy thoughts',
+      'sleep and dream peacefully' ],
+]
+
+for list in lists do
+    puts "The list is: #{commify_series(list)}."
+end
+
+
+# @@PLEAC@@_4.3
+#   (note: AFAIK Ruby doesn't allow gory change of Array length)
+# grow the array by assigning nil to past the end of array
+ary[new_size-1] = nil
+# shrink the array by slicing it down
+ary.slice!(new_size..-1)
+# init the array with given size
+Array.new(number_of_elems)
+# assign to an element past the original end enlarges the array
+ary[index_new_last_elem] = value
+
+def what_about_that_array(a)
+    print "The array now has ", a.size, " elements.\n"
+    # Index of last element is not really interesting in Ruby
+    print "Element #3 is `#{a[3]}'.\n"
+end
+people = %w(Crosby Stills Nash Young)
+what_about_that_array(people)
+
+
+# @@PLEAC@@_4.4
+# OO style
+bad_users.each { |user|
+    complain(user)
+}
+# or, functional style
+for user in bad_users
+    complain(user)
+end
+
+for var in ENV.keys.sort
+    puts "#{var}=#{ENV[var]}"
+end
+
+for user in all_users
+    disk_space = get_usage(user)
+    if (disk_space > MAX_QUOTA)
+        complain(user)
+    end
+end
+
+for l in IO.popen("who").readlines
+    print l if l =~ /^gc/ 
+end
+
+# we can mimic the obfuscated Perl way
+while fh.gets               # $_ is set to the line just read
+    chomp                   # $_ has a trailing \n removed, if it had one
+    split.each { |w|        # $_ is split on whitespace
+                            # but $_ is not set to each chunk as in Perl
+        print w.reverse
+    }
+end
+# ...or use a cleaner way
+for l in fh.readlines
+    l.chomp.split.each { |w| print w.reverse }
+end
+
+# same drawback as in problem 1.4, we can't mutate a Numeric...
+array.collect! { |v| v - 1 }
+
+a = [ .5, 3 ]; b = [ 0, 1 ]
+for ary in [ a, b ]
+    ary.collect! { |v| v * 7 }
+end
+puts "#{a.join(' ')} #{b.join(' ')}"
+
+# we can mutate Strings, cool; we need a trick for the scalar
+for ary in [ [ scalar ], array, hash.values ]
+    ary.each { |v| v.strip! }     # String#strip rules :)
+end
+
+
+# @@PLEAC@@_4.5
+# not relevant in Ruby since we have always references
+for item in array
+    # do somethingh with item
+end
+
+
+# @@PLEAC@@_4.6
+unique = list.uniq
+
+# generate a list of users logged in, removing duplicates
+users = `who`.collect { |l| l =~ /(\w+)/; $1 }.sort.uniq
+puts("users logged in: #{commify_series(users)}")  # see 4.2 for commify_series
+
+
+# @@PLEAC@@_4.7
+a - b
+# [ 1, 1, 2, 2, 3, 3, 3, 4, 5 ] - [ 1, 2, 4 ]  ->  [3, 5]
+
+
+# @@PLEAC@@_4.8
+union = a | b
+intersection = a & b
+difference = a - b
+
+
+# @@PLEAC@@_4.9
+array1.concat(array2)
+# if you will assign to another object, better use:
+new_ary = array1 + array2
+
+members = [ "Time", "Flies" ]
+initiates =  [ "An", "Arrow" ]
+members += initiates
+
+members = [ "Time", "Flies" ]
+initiates = [ "An", "Arrow" ]
+members[2,0] = [ "Like", initiates ].flatten
+
+members[0] = "Fruit"
+members[3,2] = "A", "Banana"
+
+
+# @@PLEAC@@_4.10
+reversed = ary.reverse
+
+ary.reverse_each { |e|
+    # do something with e
+}
+
+descending = ary.sort.reverse
+descending = ary.sort { |a,b| b <=> a }
+
+
+# @@PLEAC@@_4.11
+# remove n elements from front of ary (shift n)
+front = ary.slice!(0, n)
+
+# remove n elements from the end of ary (pop n)
+end_ = ary.slice!(-n .. -1)
+
+# let's extend the Array class, to make that useful
+class Array
+    def shift2()
+        slice!(0 .. 1)     # more symetric with pop2...
+    end
+    def pop2()
+        slice!(-2 .. -1)
+    end
+end
+
+friends = %w(Peter Paul Mary Jim Tim)
+this, that = friends.shift2
+
+beverages = %w(Dew Jolt Cola Sprite Fresca)
+pair = beverages.pop2
+
+
+# @@PLEAC@@_4.12
+# use Enumerable#detect (or the synonym Enumerable#find)
+highest_eng = employees.detect { |emp| emp.category == 'engineer' }
+
+
+# @@PLEAC@@_4.13
+# use Enumerable#select (or the synonym Enumerable#find_all)
+bigs = nums.select { |i| i > 1_000_000 }
+pigs = users.keys.select { |k| users[k] > 1e7 }
+
+matching = `who`.select { |u| u =~ /^gnat / }
+
+engineers = employees.select { |e| e.position == 'Engineer' }
+
+secondary_assistance = applicants.select { |a|
+    a.income >= 26_000 && a.income < 30_000
+}
+
+
+# @@PLEAC@@_4.14
+# normally you would have an array of Numeric (Float or
+# Fixnum or Bignum), so you would use:
+sorted = unsorted.sort
+# if you have strings representing Integers or Floats
+# you may specify another sort method:
+sorted = unsorted.sort { |a,b| a.to_f <=> b.to_f }
+
+# let's use the list of my own PID's
+`ps ux`.split("\n")[1..-1].
+    select { |i| i =~ /^#{ENV['USER']}/ }.
+    collect { |i| i.split[1] }.
+    sort { |a,b| a.to_i <=> b.to_i }.each { |i| puts i }
+puts "Select a process ID to kill:"
+pid = gets.chomp
+raise "Exiting ... \n" unless pid && pid =~ /^\d+$/
+Process.kill('TERM', pid.to_i)
+sleep 2
+Process.kill('KILL', pid.to_i)
+
+descending = unsorted.sort { |a,b| b.to_f <=> a.to_f }
+
+
+# @@PLEAC@@_4.15
+ordered = unordered.sort { |a,b| compare(a,b) }
+
+precomputed = unordered.collect { |e| [compute, e] }
+ordered_precomputed = precomputed.sort { |a,b| a[0] <=> b[0] }
+ordered = ordered_precomputed.collect { |e| e[1] }
+
+ordered = unordered.collect { |e| [compute, e] }.
+    sort { |a,b| a[0] <=> b[0] }.
+    collect { |e| e[1] }
+
+for employee in employees.sort { |a,b| a.name <=> b.name }
+    print employee.name, " earns \$ ", employee.salary, "\n"
+end
+
+# Beware! `0' is true in Ruby.
+# For chaining comparisons, you may use Numeric#nonzero?, which
+# returns num if num is not zero, nil otherwise
+sorted = employees.sort { |a,b| (a.name <=> b.name).nonzero? || b.age <=> a.age }
+
+users = []
+# getpwent is not wrapped in Ruby... let's fallback
+IO.readlines('/etc/passwd').each { |u| users << u.split(':') }
+users.sort! { |a,b| a[0] <=> b[0] }
+for user in users
+    puts user[0]
+end
+
+sorted = names.sort { |a,b| a[1, 1] <=> b[1, 1] }
+sorted = strings.sort { |a,b| a.length <=> b.length }
+
+# let's show only the compact version
+ordered = strings.collect { |e| [e.length, e] }.
+    sort { |a,b| a[0] <=> b[0] }.
+    collect { |e| e[1] }
+
+ordered = strings.collect { |e| [/\d+/.match(e)[0].to_i, e] }.
+    sort { |a,b| a[0] <=> b[0] }.
+    collect { |e| e[1] }
+
+print `cat /etc/passwd`.collect { |e| [e, e.split(':').indexes(3,2,0)].flatten }.
+    sort { |a,b| (a[1] <=> b[1]).nonzero? || (a[2] <=> b[2]).nonzero? || a[3] <=> b[3] }.
+    collect { |e| e[0] }
+
+
+# @@PLEAC@@_4.16
+circular.unshift(circular.pop)        # the last shall be first
+circular.push(circular.shift)         # and vice versa
+
+def grab_and_rotate(l)
+    l.push(ret = l.shift)
+    ret
+end
+
+processes = [1, 2, 3, 4, 5]
+while (1)
+    process = grab_and_rotate(processes)
+    puts "Handling process #{process}"
+    sleep 1
+end
+
+
+# @@PLEAC@@_4.17
+def fisher_yates_shuffle(a)
+    (a.size-1).downto(1) { |i|
+        j = rand(i+1)
+        a[i], a[j] = a[j], a[i] if i != j
+    }
+end
+
+def naive_shuffle(a)
+    for i in 0...a.size
+        j = rand(a.size)
+        a[i], a[j] = a[j], a[i]
+    end
+end
+
+
+# @@PLEAC@@_4.18
+#!/usr/bin/env ruby
+# example 4-2 words
+# words - gather lines, present in colums
+
+# class to encapsulate the word formatting from the input
+class WordFormatter
+    def initialize(cols)
+        @cols = cols
+    end
+
+    # helper to return the length of the longest word in the wordlist
+    def maxlen(wordlist)
+        max = 1
+        for word in wordlist
+            if word.length > max
+                max = word.length
+            end
+        end
+        max
+    end
+
+    # process the wordlist and print it formmated into columns
+    def output(wordlist)
+        collen = maxlen(wordlist) + 1
+        columns = @cols / collen
+        columns = 1 if columns == 0
+        rows = (wordlist.length + columns - 1) / columns
+        # now process each item, picking out proper piece for this position
+        0.upto(rows * columns - 1) { |item|
+            target = (item % columns) * rows + (item / columns)
+            eol = ((item+1) % columns == 0)
+            piece = wordlist[target] || ""
+            piece = piece.ljust(collen) unless eol
+            print piece
+            puts if eol
+        }
+        # no need to finish it up, because eol is always true for the last element
+    end
+end
+
+# get nr of chars that fit in window or console, see PLEAC 15.4
+# not portable -- linux only (?)
+def getWinCharWidth()
+    buf = "\0" * 8
+    $stdout.ioctl(0x5413, buf)
+    ws_row, ws_col, ws_xpixel, ws_ypixel = buf.unpack("$4")
+    ws_col || 80
+rescue
+    80
+end
+
+# main program
+cols = getWinCharWidth()
+formatter = WordFormatter.new(cols)
+words = readlines()
+words.collect! { |line|
+    line.chomp
+}
+formatter.output(words)
+
+
+# @@PLEAC@@_4.19
+# In ruby, Fixnum's are automatically converted to Bignum's when
+# needed, so there is no need for an extra module
+def factorial(n)
+    s = 1
+    while n > 0
+        s *= n
+        n -= 1
+    end
+    s
+end
+
+puts factorial(500)
+
+#---------------------------------------------------------
+# Example 4-3. tsc-permute
+# tsc_permute: permute each word of input
+def permute(items, perms)
+    unless items.length > 0
+        puts perms.join(" ")
+    else
+        for i in items
+            newitems = items.dup
+            newperms = perms.dup
+            newperms.unshift(newitems.delete(i))
+            permute(newitems, newperms)
+        end
+    end
+end
+# In ruby the main program must be after all definitions it is using
+permute(ARGV, [])
+
+#---------------------------------------------------------
+# mjd_permute: permute each word of input
+
+def factorial(n)
+    s = 1
+    while n > 0
+        s *= n
+        n -= 1
+    end
+    s
+end
+
+# we use a class with a class variable store the private cache
+# for the results of the factorial function.
+class Factorial
+    @@fact = [ 1 ]
+    def Factorial.compute(n)
+        if @@fact[n]
+            @@fact[n]
+        else
+            @@fact[n] = n * Factorial.compute(n - 1)
+        end
+    end
+end
+
+#---------------------------------------------------------
+# Example 4-4- mjd-permute
+# n2pat(n, len): produce the N-th pattern of length len
+
+# We must use a lower case letter as parameter N, otherwise it is
+# handled as constant Length is the length of the resulting
+# array, not the index of the last element (length -1) like in
+# the perl example.
+def n2pat(n, length)
+    pat = []
+    i = 1
+    while i <= length
+        pat.push(n % i)
+        n /= i
+        i += 1
+    end
+    pat
+end
+
+# pat2perm(pat): turn pattern returned by n2pat() into
+# permutation of integers.
+def pat2perm(pat)
+    source = (0 .. pat.length - 1).to_a
+    perm = []
+    perm.push(source.slice!(pat.pop)) while pat.length > 0
+    perm
+end
+
+def n2perm(n, len)
+    pat2perm(n2pat(n,len))
+end
+
+# In ruby the main program must be after all definitions
+while gets
+    data = split
+    # the perl solution has used $#data, which is length-1
+    num_permutations = Factorial.compute(data.length())
+    0.upto(num_permutations - 1) do |i|
+        # in ruby we can not use an array as selector for an array
+        # but by exchanging the two arrays, we can use the collect method
+        # which returns an array with the result of all block invocations
+        permutation = n2perm(i, data.length).collect {
+            |j| data[j]
+        }
+        puts permutation.join(" ")
+    end
+end
+
+
+# @@PLEAC@@_5.0
+age = { "Nat",   24,
+        "Jules", 25,
+        "Josh",  17  }
+
+age["Nat"]   = 24
+age["Jules"] = 25
+age["Josh"]  = 17
+
+food_color = {
+    "Apple"  => "red",
+    "Banana" => "yellow",
+    "Lemon"  => "yellow",
+    "Carrot" => "orange"
+             }
+
+# In Ruby, you cannot avoid the double or simple quoting
+# while manipulatin hashes
+
+
+# @@PLEAC@@_5.1
+hash[key] = value
+
+food_color["Raspberry"] = "pink"
+puts "Known foods:", food_color.keys
+
+
+# @@PLEAC@@_5.2
+# does hash have a value for key ?
+if (hash.has_key?(key))
+    # it exists
+else
+    # it doesn't
+end
+
+[ "Banana", "Martini" ].each { |name|
+    print name, " is a ", food_color.has_key?(name) ? "food" : "drink", "\n"
+}
+
+age = {}
+age['Toddler'] = 3
+age['Unborn'] = 0
+age['Phantasm'] = nil
+
+for thing in ['Toddler', 'Unborn', 'Phantasm', 'Relic']
+    print "#{thing}: "
+    print "Has-key " if age.has_key?(thing)
+    print "True " if age[thing]
+    print "Nonzero " if age[thing] && age[thing].nonzero?
+    print "\n"
+end
+
+#=>
+# Toddler: Has-key True Nonzero 
+# Unborn: Has-key True 
+# Phantasm: Has-key 
+# Relic: 
+
+# You use Hash#has_key? when you use Perl's exists -> it checks
+# for existence of a key in a hash.
+# All Numeric are "True" in ruby, so the test doesn't have the
+# same semantics as in Perl; you would use Numeric#nonzero? to
+# achieve the same semantics (false if 0, true otherwise).
+
+
+# @@PLEAC@@_5.3
+food_color.delete("Banana")
+
+
+# @@PLEAC@@_5.4
+hash.each { |key, value|
+    # do something with key and value
+}
+
+hash.each_key { |key|
+    # do something with key
+}
+
+food_color.each { |food, color|
+    puts "#{food} is #{color}"
+}
+
+food_color.each_key { |food|
+    puts "#{food} is #{food_color[food]}"
+}
+
+# IMO this demonstrates that OO style is by far more readable
+food_color.keys.sort.each { |food|
+    puts "#{food} is #{food_color[food]}."
+}
+
+#-----------------------------
+#!/usr/bin/ruby
+# countfrom - count number of messages from each sender
+
+# Default value is 0
+from = Hash.new(0)
+while gets
+    /^From: (.*)/ and from[$1] += 1
+end
+
+# More useful to sort by number of received mail by person
+from.sort {|a,b| b[1]<=>a[1]}.each { |v|
+    puts "#{v[1]}: #{v[0]}"
+}
+#-----------------------------
+
+
+# @@PLEAC@@_5.5
+# You may use the built-in 'inspect' method this way:
+p hash
+
+# Or do it the Cookbook way:
+hash.each { |k,v| puts "#{k} => #{v}" }
+
+# Sorted by keys
+hash.sort.each { |e| puts "#{e[0]} => #{e[1]}" }
+# Sorted by values
+hash.sort{|a,b| a[1]<=>b[1]}.each { |e| puts "#{e[0]} => #{e[1]}" }
+
+
+# @@PLEAC@@_5.7
+ttys = Hash.new
+for i in `who`
+    user, tty = i.split
+    (ttys[user] ||= []) << tty               # see problems_ruby for more infos
+end
+ttys.keys.sort.each { |k|
+    puts "#{k}: #{commify_series(ttys[k])}"  # from 4.2
+}
+
+
+# @@PLEAC@@_5.8
+surname = { "Mickey" => "Mantle", "Babe" => "Ruth" }
+puts surname.index("Mantle")
+
+# If you really needed to 'invert' the whole hash, use Hash#invert
+
+#-----------------------------
+#!/usr/bin/ruby -w
+# foodfind - find match for food or color
+
+given = ARGV.shift or raise "usage: foodfind food_or_color"
+
+color = {
+    "Apple"  => "red",
+    "Banana" => "yellow",
+    "Lemon"  => "yellow",
+    "Carrot" => "orange",
+}
+
+if (color.has_key?(given))
+    puts "#{given} is a food with color #{color[given]}."
+end
+if (color.has_value?(given))
+    puts "#{color.index(given)} is a food with color #{given}."
+end
+#-----------------------------
+
+
+# @@PLEAC@@_5.9
+# Sorted by keys (Hash#sort gives an Array of pairs made of each key,value)
+food_color.sort.each { |f|
+    puts "#{f[0]} is #{f[1]}."
+}
+
+# Sorted by values
+food_color.sort { |a,b| a[1] <=> b[1] }.each { |f|
+    puts "#{f[0]} is #{f[1]}."
+}
+
+# Sorted by length of values
+food_color.sort { |a,b| a[1].length <=> b[1].length }.each { |f|
+    puts "#{f[0]} is #{f[1]}."
+}
+
+
+# @@PLEAC@@_5.10
+merged = a.clone.update(b)        # because Hash#update changes object in place
+
+drink_color = { "Galliano"  => "yellow", "Mai Tai" => "blue" }
+ingested_color = drink_color.clone.update(food_color)
+
+substance_color = {}
+for i in [ food_color, drink_color ]
+    i.each_key { |k|
+        if substance_color.has_key?(k)
+            puts "Warning: #{k} seen twice.  Using the first definition."
+            next
+        end
+        substance_color[k] = 1
+    }
+end
+
+
+# @@PLEAC@@_5.11
+common = hash1.keys & hash2.keys
+
+this_not_that = hash1.keys - hash2.keys
+
+
+# @@PLEAC@@_5.12
+# no problem here, Ruby handles any kind of object for key-ing
+# (it takes Object#hash, which defaults to Object#id)
+
+
+# @@PLEAC@@_5.13
+# AFAIK, not possible in Ruby
+
+
+# @@PLEAC@@_5.14
+# Be careful, the following is possible only because Fixnum objects are
+# special (documentation says: there is effectively only one Fixnum object
+# instance for any given integer value).
+count = Hash.new(0)
+array.each { |e|
+    count[e] += 1
+}
+
+
+# @@PLEAC@@_5.15
+father = {
+    "Cain"      , "Adam",
+    "Abel"      , "Adam",
+    "Seth"      , "Adam",
+    "Enoch"     , "Cain",
+    "Irad"      , "Enoch",
+    "Mehujael"  , "Irad",
+    "Methusael" , "Mehujael",
+    "Lamech"    , "Methusael",
+    "Jabal"     , "Lamech",
+    "Jubal"     , "Lamech",
+    "Tubalcain" , "Lamech",
+    "Enos"      , "Seth",
+}
+
+while gets
+    chomp
+    begin
+        print $_, " "
+    end while $_ = father[$_]
+    puts
+end
+
+children = {}
+father.each { |k,v|
+    (children[v] ||= []) << k
+}
+while gets
+    chomp
+    puts "#{$_} begat #{(children[$_] || ['Nobody']).join(', ')}.\n"
+end
+
+includes = {}
+files.each { |f|
+    begin
+        for l in IO.readlines(f)
+            next unless l =~ /^\s*#\s*include\s*<([^>]+)>/
+            (includes[$1] ||= []) << f
+        end
+    rescue SystemCallError
+        $stderr.puts "#$! (skipping)"
+    end
+}
+
+include_free = includes.values.flatten.uniq - includes.keys
+
+
+# @@PLEAC@@_5.16
+# dutree - print sorted intented rendition of du output
+#% dutree
+#% dutree /usr
+#% dutree -a
+#% dutree -a /bin
+
+# The DuNode class collects all information about a directory,
+# and provides some convenience methods
+class DuNode
+
+    attr_reader :name
+    attr_accessor :size
+    attr_accessor :kids
+
+    def initialize(name)
+        @name = name
+        @kids = []
+        @size = 0
+    end
+
+    # support for sorting nodes with side
+    def size_compare(node2)
+        @size <=> node2.size
+    end
+
+    def basename
+        @name.sub(/.*\//, "")
+    end
+
+    #returns substring before last "/", nil if not there
+    def parent
+        p = @name.sub(/\/[^\/]+$/,"")
+        if p == @name
+            nil
+        else
+            p
+        end
+    end
+
+end
+
+# The DuTree does the acdtual work of
+# getting the input, parsing it, builging up a tree
+# and format it for output
+class Dutree
+
+    attr_reader :topdir
+
+    def initialize
+        @nodes = Hash.new
+        @dirsizes = Hash.new(0)
+        @kids = Hash.new([])
+    end
+
+    # get a node by name, create it if it does not exist yet
+    def get_create_node(name)
+        if @nodes.has_key?(name)
+            @nodes[name]
+        else
+            node = DuNode.new(name)
+            @nodes[name] = node
+            node
+        end
+    end
+
+    # run du, read in input, save sizes and kids
+    # stores last directory read in instance variable topdir
+    def input(arguments)
+        name = ""
+        cmd = "du " + arguments.join(" ")
+        IO.popen(cmd) { |pipe|
+            pipe.each { |line|
+                size, name = line.chomp.split(/\s+/, 2)
+                node = get_create_node(name)
+                node.size = size.to_i
+                @nodes[name] = node
+                parent = node.parent
+                if parent
+                    get_create_node(parent).kids.push(node)
+                end
+            }
+        }
+        @topdir = @nodes[name]
+    end
+
+    # figure out how much is taken in each directory
+    # that isn't stored in the subdirectories. Add a new
+    # fake kid called "." containing that much.
+    def get_dots(node)
+        cursize = node.size
+        for kid in node.kids
+            cursize -=  kid.size
+            get_dots(kid)
+        end
+        if node.size != cursize
+            newnode = get_create_node(node.name + "/.")
+            newnode.size = cursize
+            node.kids.push(newnode)
+        end
+    end
+
+    # recursively output everything
+    # passing padding and number width as well
+    # on recursive calls
+    def output(node, prefix="", width=0)
+        line = sprintf("%#{width}d %s", node.size, node.basename)
+        puts(prefix + line)
+        prefix += line.sub(/\d /, "| ")
+        prefix.gsub!(/[^|]/, " ")
+        if node.kids.length > 0     # not a bachelor node
+            kids = node.kids
+            kids.sort! { |a,b|
+                b.size_compare(a)
+            }
+            width = kids[0].size.to_s.length
+            for kid in kids
+                output(kid, prefix, width)
+            end
+        end
+    end
+
+end
+
+tree = Dutree.new
+tree.input(ARGV)
+tree.get_dots(tree.topdir)
+tree.output(tree.topdir)
+
+
+# @@PLEAC@@_6.0
+# The verbose version are match, sub, gsub, sub! and gsub!;
+# pattern needs to be a Regexp object; it yields a MatchData
+# object.
+pattern.match(string)
+string.sub(pattern, replacement)
+string.gsub(pattern, replacement)
+# As usual in Ruby, sub! does the same as sub but also modifies
+# the object, the same for gsub!/gsub.
+
+# Sugared syntax yields the position of the match (or nil if no
+# match). Note that the object at the right of the operator needs
+# not to be a Regexp object (it can be a String). The "dont
+# match" operator yields true or false.
+meadow =~ /sheep/   # position of the match, nil if no match
+meadow !~ /sheep/   # true if doesn't match, false if it does
+# There is no sugared version for the substitution
+
+meadow =~ /\bovines?\b/i and print "Here be sheep!"
+
+string = "good food"
+string.sub!(/o*/, 'e')
+
+# % echo ababacaca | ruby -ne 'puts $& if /(a|ba|b)+(a|ac)+/'
+# ababa
+
+# The "global" (or "multiple") match is handled by String#scan
+scan (/(\d+)/) {
+    puts "Found number #{$1}"
+}
+
+# String#scan yields an Array if not used with a block
+numbers = scan(/\d+/)
+
+digits = "123456789"
+nonlap = digits.scan(/(\d\d\d)/)
+yeslap = digits.scan(/(?=(\d\d\d))/)
+puts "Non-overlapping:  #{nonlap.join(' ')}"
+puts "Overlapping:      #{yeslap.join(' ')}";
+# Non-overlapping:  123 456 789
+# Overlapping:      123 234 345 456 567 678 789
+
+string = "And little lambs eat ivy"
+string =~ /l[^s]*s/
+puts "(#$`) (#$&) (#$')"
+# (And ) (little lambs) ( eat ivy)
+
+
+# @@PLEAC@@_6.1
+# Ruby doesn't have the same problem:
+dst = src.sub('this', 'that')
+
+progname = $0.sub('^.*/', '')
+
+bindirs = %w(/usr/bin /bin /usr/local/bin)
+libdirs = bindirs.map { |l| l.sub('bin', 'lib') }
+
+
+# @@PLEAC@@_6.3
+/\S+/               # as many non-whitespace bytes as possible
+/[A-Za-z'-]+/       # as many letters, apostrophes, and hyphens
+
+/\b([A-Za-z]+)\b/   # usually best
+/\s([A-Za-z]+)\s/   # fails at ends or w/ punctuation
+
+
+# @@PLEAC@@_6.4
+require 'socket'
+str = 'www.ruby-lang.org and www.rubygarden.org'
+re = /
+      (               # capture the hostname in $1
+        (?:           # these parens for grouping only
+          (?! [-_] )  # lookahead for neither underscore nor dash
+          [\w-] +     # hostname component
+          \.          # and the domain dot
+        ) +           # now repeat that whole thing a bunch of times
+        [A-Za-z]      # next must be a letter
+        [\w-] +       # now trailing domain part
+      )               # end of $1 capture
+     /x               # /x for nice formatting
+
+str.gsub! re do       # pass a block to execute replacement
+    host = TCPsocket.gethostbyname($1)
+    "#{$1} [#{host[3]}]"
+end
+
+puts str
+#-----------------------------
+# to match whitespace or #-characters in an extended re you need to escape
+# them.
+
+foo = 42
+str = 'blah #foo# blah'
+str.gsub! %r/       # replace
+              \#    #   a pound sign
+              (\w+) #   the variable name
+              \#    #   another pound sign
+          /x do
+              eval $1           # with the value of a local variable
+          end
+puts str  # => blah 42 blah
+
+
+# @@PLEAC@@_6.5
+# The 'g' modifier doesn't exist in Ruby, a regexp can't be used
+# directly in a while loop; instead, use String#scan { |match| .. } 
+fish = 'One fish two fish red fish blue fish'
+WANT = 3
+count = 0
+fish.scan(/(\w+)\s+fish\b/i) {
+    if (count += 1) == WANT
+        puts "The third fish is a #{$1} one."
+    end
+}
+
+if fish =~ /(?:\w+\s+fish\s+){2}(\w+)\s+fish/i
+    puts "The third fish is a #{$1} one."
+end
+
+pond = 'One fish two fish red fish blue fish'
+# String#scan without a block gives an array of matches, each match
+# being an array of all the specified groups
+colors = pond.scan(/(\w+)\s+fish\b/i).flatten  # get all matches
+color  = colors[2]                          # then the one we want
+# or without a temporary array
+color = pond.scan(/(\w+)\s+fish\b/i).flatten[2]  # just grab element 3
+puts "The third fish in the pond is #{color}."
+
+count = 0
+fishes = 'One fish two fish red fish blue fish'
+evens = fishes.scan(/(\w+)\s+fish\b/i).select { (count+=1) % 2 == 0 }
+print "Even numbered fish are #{evens.join(' ')}."
+
+count = 0
+fishes.gsub(/
+   \b               # makes next \w more efficient
+   ( \w+ )          # this is what we\'ll be changing
+   (
+     \s+ fish \b
+   )
+            /x) {
+    if (count += 1) == 4
+        'sushi' + $2
+    else
+        $1 + $2
+    end
+}
+
+pond = 'One fish two fish red fish blue fish swim here.'
+puts "Last fish is #{pond.scan(/\b(\w+)\s+fish\b/i).flatten[-1]}"
+
+/
+    A               # find some pattern A
+    (?!             # mustn\'t be able to find
+        .*          # something
+        A           # and A
+    )
+    $               # through the end of the string
+/x
+
+# The "s" perl modifier is "m" in Ruby (not very nice since there is
+# also an "m" in perl..)
+pond = "One fish two fish red fish blue fish swim here."
+if (pond =~ /
+                    \b  (  \w+) \s+ fish \b
+                (?! .* \b fish \b )
+            /mix)
+    puts "Last fish is #{$1}."
+else
+    puts "Failed!"
+end
+
+
+# @@PLEAC@@_6.6
+#-----------------------------
+#!/usr/bin/ruby -w
+# killtags - very bad html killer
+$/ = nil;                              # each read is whole file
+while file = gets() do
+    file.gsub!(/<.*?>/m,'');           # strip tags (terribly)
+    puts file                          # print file to STDOUT
+end
+#-----------------------------
+#!/usr/bin/ruby -w
+#headerfy - change certain chapter headers to html
+$/ = ''
+while file = gets() do
+    pattern = /
+                  \A                   # start of record
+                  (                    # capture in $1
+                      Chapter          # text string
+                      \s+              # mandatory whitespace
+                      \d+              # decimal number
+                      \s*              # optional whitespace
+                      :                # a real colon
+                      . *              # anything not a newline till end of line
+                  )
+               /x
+    puts file.gsub(pattern,'<H1>\1</H1>')
+end
+#-----------------------------
+#% ruby -00pe "gsub!(/\A(Chapter\s+\d+\s*:.*)/,'<H1>\1</H1>')" datafile
+
+#!/usr/bin/ruby -w
+#-----------------------------
+for file in ARGV
+    file = File.open(ARGV.shift)
+    while file.gets('') do             # each read is a paragraph
+        print "chunk #{$.} in $ARGV has <<#{$1}>>\n" while /^START(.*?)^END/m
+    end                                # /m activates the multiline mode
+end
+#-----------------------------
+
+# @@PLEAC@@_6.7
+#-----------------------------
+$/ = nil;
+file = File.open("datafile")
+chunks = file.gets.split(/pattern/)
+#-----------------------------
+# .Ch, .Se and .Ss divide chunks of STDIN
+chunks = gets(nil).split(/^\.(Ch|Se|Ss)$/)
+print "I read #{chunks.size} chunks.\n"
+#-----------------------------
+
+
+# @@PLEAC@@_6.8
+while gets
+    if ~/BEGIN/ .. ~/END/
+        # line falls between BEGIN and END inclusive
+    end
+end
+
+while gets
+    if ($. == firstnum) .. ($. == lastnum)
+        # operate between firstnum and lastnum line number
+    end
+end
+
+# in ruby versions prior to 1.8, the above two conditional
+# expressions could be shortened to:
+#     if /BEGIN/ .. /END/
+# and
+#     if firstnum .. lastnum
+# but these now only work this way from the command line  
+
+#-----------------------------
+
+while gets
+    if ~/BEGIN/ ... ~/END/
+        # line falls between BEGIN and END on different lines
+    end
+end
+
+while gets
+    if ($. == first) ... ($. == last)
+        # operate between first and last line number on different lines
+    end
+end
+
+#-----------------------------
+# command-line to print lines 15 through 17 inclusive (see below)
+ruby -ne 'print if 15 .. 17' datafile
+
+# print out all <XMP> .. </XMP> displays from HTML doc
+while gets
+    print if ~%r#<XMP>#i .. ~%r#</XMP>#i;
+end
+    
+# same, but as shell command
+# ruby -ne 'print if %r#<XMP>#i .. %r#</XMP>#i' document.html
+#-----------------------------
+# ruby -ne 'BEGIN { $top=3; $bottom=5 }; \
+#     print if $top .. $bottom' /etc/passwd                 #  FAILS
+# ruby -ne 'BEGIN { $top=3; $bottom=5 }; \
+#     print if $. == $top .. $. ==  $bottom' /etc/passwd    # works
+# ruby -ne 'print if 3 .. 5' /etc/passwd                    # also works
+#-----------------------------
+print if ~/begin/ .. ~/end/;
+print if ~/begin/ ... ~/end/;
+#-----------------------------
+while gets
+    $in_header = $. == 1  .. ~/^$/ ? true : false
+    $in_body   = ~/^$/ .. ARGF.eof ? true : false
+end
+#-----------------------------
+seen = {}
+ARGF.each do |line|
+    next unless line =~ /^From:?\s/i .. line =~ /^$/;
+    line.scan(%r/([^<>(),;\s]+\@[^<>(),;\s]+)/).each do |addr|
+        puts addr unless seen[addr]
+        seen[addr] ||= 1 
+    end
+end
+
+
+# @@PLEAC@@_6.9
+def glob2pat(globstr)
+    patmap = {
+        '*' => '.*',
+        '?' => '.',
+        '[' => '[',
+        ']' => ']',
+    }
+    globstr.gsub!(/(.)/) { |c| patmap[c] || Regexp::escape(c) }
+    '^' + globstr + '$'
+end
+
+
+# @@PLEAC@@_6.10
+# avoid interpolating patterns like this if the pattern
+# isn't going to change:
+pattern = ARGV.shift
+ARGF.each do |line|
+    print line if line =~ /#{pattern}/
+end
+
+# the above creates a new regex each iteration. Instead,
+# use the /o modifier so the regex is compiled only once
+
+pattern = ARGV.shift
+ARGF.each do |line|
+    print line if line =~ /#{pattern}/o
+end
+
+#-----------------------------
+
+#!/usr/bin/ruby
+# popgrep1 - grep for abbreviations of places that say "pop"
+# version 1: slow but obvious way
+popstates = %w(CO ON MI WI MN)
+ARGF.each do |line|
+    popstates.each do |state|
+        if line =~ /\b#{state}\b/
+            print line
+            last
+        end
+    end
+end
+
+#-----------------------------
+#!/usr/bin/ruby
+# popgrep2 - grep for abbreviations of places that say "pop"
+# version 2: eval strings; fast but hard to quote
+popstates = %w(CO ON MI WI MN)
+code = "ARGF.each do |line|\n"
+popstates.each do |state|
+    code += "\tif line =~ /\\b#{state}\\b/; print(line); next; end\n"
+end
+code += "end\n"
+print "CODE IS\n---\n#{code}\n---\n" if false # turn on for debugging
+eval code
+
+# CODE IS
+# ---
+# ARGF.each do |line|
+#         if line =~ /\bCO\b/; print(line); next; end
+#         if line =~ /\bON\b/; print(line); next; end
+#         if line =~ /\bMI\b/; print(line); next; end
+#         if line =~ /\bWI\b/; print(line); next; end
+#         if line =~ /\bMN\b/; print(line); next; end
+# end
+# 
+# ---
+
+## alternatively, the same idea as above but compiling 
+## to a case statement: (not in perlcookbook)
+#!/usr/bin/ruby -w
+# popgrep2.5 - grep for abbreviations of places that say "pop"
+# version 2.5: eval strings; fast but hard to quote
+popstates = %w(CO ON MI WI MN)
+code = "ARGF.each do |line|\n    case line\n"
+popstates.each do |state|
+    code += "        when /\\b#{state}\\b/ : print line\n"
+end
+code += "    end\nend\n"
+print "CODE IS\n---\n#{code}\n---\n" if false # turn on for debugging
+eval code
+
+# CODE IS
+# ---
+# ARGF.each do |line|
+#     case line
+#         when /\bCO\b/ : print line
+#         when /\bON\b/ : print line
+#         when /\bMI\b/ : print line
+#         when /\bWI\b/ : print line
+#         when /\bMN\b/ : print line
+#     end
+# end
+# 
+# ---
+
+# Note: (above) Ruby 1.8+ allows the 'when EXP : EXPR' on one line
+# with the colon separator.
+
+#-----------------------------
+#!/usr/bin/ruby
+# popgrep3 - grep for abbreviations of places that say "pop"
+# version3: build a match_any function
+popstates = %w(CO ON MI WI MN)
+expr = popstates.map{|e|"line =~ /\\b#{e}\\b/"}.join('||')
+eval "def match_any(line); #{expr};end"
+ARGF.each do |line|
+    print line if match_any(line)
+end
+#-----------------------------
+
+##  building a match_all function is a trivial
+##  substitution of && for ||
+##  here is a generalized example:
+#!/usr/bin/ruby -w
+## grepauth - print lines that mention both foo and bar
+class MultiMatch 
+    def initialize(*patterns)
+        _any = build_match('||',patterns)
+        _all = build_match('&&',patterns)
+        eval "def match_any(line);#{_any};end\n"
+        eval "def match_all(line);#{_all};end\n"
+      end
+    def build_match(sym,args)
+        args.map{|e|"line =~ /#{e}/"}.join(sym)
+    end
+end
+
+mm = MultiMatch.new('foo','bar')
+ARGF.each do |line|
+    print line if mm.match_all(line)
+end
+#-----------------------------
+
+#!/usr/bin/ruby
+# popgrep4 - grep for abbreviations of places that say "pop"
+# version4: pretty fast, but simple: compile all re's first:
+popstates = %w(CO ON MI WI MN)
+popstates = popstates.map{|re| %r/\b#{re}\b/}
+ARGF.each do |line|
+    popstates.each do |state_re|
+        if line =~ state_re
+            print line
+            break
+        end
+    end
+end
+
+## speeds trials on the jargon file(412): 26006 lines, 1.3MB
+## popgrep1   => 7.040s
+## popgrep2   => 0.656s
+## popgrep2.5 => 0.633s
+## popgrep3   => 0.675s
+## popgrep4   => 1.027s
+
+# unless speed is criticial, the technique in popgrep4 is a
+# reasonable balance between speed and logical simplicity.
+
+
+# @@PLEAC@@_6.11
+begin
+    print "Pattern? "
+    pat = $stdin.gets.chomp
+    Regexp.new(pat)
+rescue 
+    warn "Invalid Pattern"
+    retry
+end
+
+
+# @@PLEAC@@_6.13
+# uses the 'amatch' extension found on:
+# http://raa.ruby-lang.org/project/amatch/
+require 'amatch'
+matcher = Amatch.new('balast')
+#$relative, $distance = 0, 1
+File.open('/usr/share/dict/words').each_line do |line|
+    print line if matcher.search(line) <= 1
+end
+__END__
+#CODE
+ballast
+ballasts
+balustrade
+balustrades
+blast
+blasted
+blaster
+blasters
+blasting
+blasts
+
+
+# @@PLEAC@@_6.14
+str.scan(/\G(\d)/).each do |token|
+    puts "found #{token}"
+end
+#-----------------------------
+n = "   49 here"
+n.gsub!(/\G /,'0')
+puts n
+#-----------------------------
+str = "3,4,5,9,120"
+str.scan(/\G,?(\d+)/).each do |num|
+    puts "Found number: #{num}"
+end
+#-----------------------------
+# Ruby doesn't have the String.pos or a /c re modifier like Perl 
+# But it does have StringScanner in the standard library (strscn)
+# which allows similar functionality:
+
+require 'strscan'
+text = 'the year 1752 lost 10 days on the 3rd of September'
+sc = StringScanner.new(text)
+while sc.scan(/.*?(\d+)/)
+    print "found: #{sc[1]}\n"   
+end
+if sc.scan(/\S+/)
+    puts "Found #{sc[0]} after last number"
+end
+#-----------------------------
+# assuming continuing from above:
+puts "The position in 'text' is: #{sc.pos}"
+sc.pos = 30
+puts "The position in 'text' is: #{sc.pos}"
+
+
+# @@PLEAC@@_6.15
+#-----------------------------
+# greedy pattern
+str.gsub!(/<.*>/m,'')   # not good
+
+# non-greedy (minimal) pattern
+str.gsub!(/<.*?>/m,'')   # not great
+
+
+#-----------------------------
+#<b><i>this</i> and <i>that</i> are important</b> Oh, <b><i>me too!</i></b>
+#-----------------------------
+%r{ <b><i>(.*?)</i></b> }mx
+#-----------------------------
+%r/BEGIN((?:(?!BEGIN).)*)END/
+#-----------------------------
+%r{ <b><i>(  (?: (?!</b>|</i>). )*  ) </i></b> }mx
+#-----------------------------
+%r{ <b><i>(  (?: (?!</[ib]>). )*  ) </i></b> }mx
+#-----------------------------
+%r{
+    <b><i> 
+    [^<]*  # stuff not possibly bad, and not possibly the end.
+    (?:
+ # at this point, we can have '<' if not part of something bad
+     (?!  </?[ib]>  )   # what we can't have
+     <                  # okay, so match the '<'
+     [^<]*              # and continue with more safe stuff
+    ) *
+    </i></b>
+ }mx
+
+
+# @@PLEAC@@_6.16
+#-----------------------------
+$/ = ""
+ARGF.each do |para|
+    para.scan %r/
+                  \b     # start at word boundary
+                  (\S+)  # find chunk of non-whitespace
+                  \b     # until a word boundary
+                  (      
+                    \s+  # followed by whitespace
+                    \1   # and that same chunk again
+                    \b   # and a word boundary
+                  ) +    # one or more times
+                /xi do
+        puts "dup word '#{$1}' at paragraph #{$.}" 
+    end
+end
+#-----------------------------
+astr = 'nobody'
+bstr = 'bodysnatcher'
+if "#{astr} #{bstr}" =~ /^(\w+)(\w+) \2(\w+)$/
+    print "#{$2} overlaps in #{$1}-#{$2}-#{$3}"
+end
+#-----------------------------
+#!/usr/bin/ruby -w
+# prime_pattern -- find prime factors of argument using patterns
+ARGV << 180
+cap = 'o' * ARGV.shift
+while cap =~ /^(oo+?)\1+$/
+    print $1.size, " "
+    cap.gsub!(/#{$1}/,'o')
+end
+puts cap.size
+#-----------------------------
+#diophantine
+# solve for 12x + 15y + 16z = 281, maximizing x
+if ('o' * 281).match(/^(o*)\1{11}(o*)\2{14}(o*)\3{15}$/)
+    x, y, z = $1.size, $2.size, $3.size
+    puts "One solution is: x=#{x}; y=#{y}; z=#{z}"
+else 
+    puts "No solution."
+end
+#    => One solution is: x=17; y=3; z=2
+
+#-----------------------------
+# using different quantifiers:
+('o' * 281).match(/^(o+)\1{11}(o+)\2{14}(o+)\3{15}$/)
+#    => One solution is: x=17; y=3; z=2
+
+('o' * 281).match(/^(o*?)\1{11}(o*)\2{14}(o*)\3{15}$/)
+#    => One solution is: x=0; y=7; z=11
+
+('o' * 281).match(/^(o+?)\1{11}(o*)\2{14}(o*)\3{15}$/)
+#    => One solution is: x=1; y=3; z=14
+
+
+# @@PLEAC@@_6.17
+# alpha OR beta
+%r/alpha|beta/
+
+# alpha AND beta
+%r/(?=.*alpha)(?=.*beta)/m
+
+# alpha AND beta,  no overlap
+%r/alpha.*beta|beta.*alpha/m
+
+# NOT beta
+%r/^(?:(?!beta).)*$/m
+
+# NOT bad BUT good
+%r/(?=(?:(?!BAD).)*$)GOOD/m
+#-----------------------------
+
+if !(string =~ /pattern/)   # ugly
+    something()
+end
+
+if string !~ /pattern/   # preferred
+    something()
+end
+
+
+#-----------------------------
+if string =~ /pat1/  && string =~ /pat2/
+    something()
+end
+#-----------------------------
+if string =~ /pat1/ || string =~ /pat2/
+    something()
+end
+#-----------------------------
+#!/usr/bin/ruby -w
+# minigrep - trivial grep
+pat = ARGV.shift
+ARGF.each do |line|
+    print line if line =~ /#{pat}/o
+end
+#-----------------------------
+ "labelled" =~ /^(?=.*bell)(?=.*lab)/m
+#-----------------------------
+$string =~ /bell/ && $string =~ /lab/
+#-----------------------------
+$murray_hill = "blah bell blah "
+if $murray_hill =~ %r{
+                         ^              # start of string
+                        (?=             # zero-width lookahead
+                            .*          # any amount of intervening stuff
+                            bell        # the desired bell string
+                        )               # rewind, since we were only looking
+                        (?=             # and do the same thing
+                            .*          # any amount of intervening stuff
+                            lab         # and the lab part
+                        )
+                     }mx                # /m means . can match newline
+
+    print "Looks like Bell Labs might be in Murray Hill!\n";
+end
+#-----------------------------
+"labelled" =~ /(?:^.*bell.*lab)|(?:^.*lab.*bell)/
+#-----------------------------
+$brand = "labelled";
+if $brand =~ %r{
+                (?:                 # non-capturing grouper
+                    ^ .*?           # any amount of stuff at the front
+                      bell          # look for a bell
+                      .*?           # followed by any amount of anything
+                      lab           # look for a lab
+                  )                 # end grouper
+            |                       # otherwise, try the other direction
+                (?:                 # non-capturing grouper
+                    ^ .*?           # any amount of stuff at the front
+                      lab           # look for a lab
+                      .*?           # followed by any amount of anything
+                      bell          # followed by a bell
+                  )                 # end grouper
+            }mx                     # /m means . can match newline
+    print "Our brand has bell and lab separate.\n";
+end
+#-----------------------------
+$map =~ /^(?:(?!waldo).)*$/s
+#-----------------------------
+$map = "the great baldo"
+if $map =~ %r{
+                ^                   # start of string
+                (?:                 # non-capturing grouper
+                    (?!             # look ahead negation
+                        waldo       # is he ahead of us now?
+                    )               # is so, the negation failed
+                    .               # any character (cuzza /s)
+                ) *                 # repeat that grouping 0 or more
+                $                   # through the end of the string
+             }mx                    # /m means . can match newline
+    print "There's no waldo here!\n";
+end
+=begin
+ 7:15am  up 206 days, 13:30,  4 users,  load average: 1.04, 1.07, 1.04
+
+USER     TTY      FROM              LOGIN@  IDLE   JCPU   PCPU  WHAT
+
+tchrist  tty1                       5:16pm 36days 24:43   0.03s  xinit
+
+tchrist  tty2                       5:19pm  6days  0.43s  0.43s  -tcsh
+
+tchrist  ttyp0    chthon            7:58am  3days 23.44s  0.44s  -tcsh
+
+gnat     ttyS4    coprolith         2:01pm 13:36m  0.30s  0.30s  -tcsh
+=end
+#% w | minigrep '^(?!.*ttyp).*tchrist'
+#-----------------------------
+%r{
+    ^                       # anchored to the start
+    (?!                     # zero-width look-ahead assertion
+        .*                  # any amount of anything (faster than .*?)
+        ttyp                # the string you don't want to find
+    )                       # end look-ahead negation; rewind to start
+    .*                      # any amount of anything (faster than .*?)
+    tchrist                 # now try to find Tom
+}x
+#-----------------------------
+#% w | grep tchrist | grep -v ttyp
+#-----------------------------
+#% grep -i 'pattern' files
+#% minigrep '(?i)pattern' files
+#-----------------------------
+
+
+# @@PLEAC@@_6.20
+ans = $stdin.gets.chomp
+re = %r/^#{Regexp.quote(ans)}/
+case 
+    when "SEND"  =~ re : puts "Action is send"
+    when "STOP"  =~ re : puts "Action is stop"
+    when "ABORT" =~ re : puts "Action is abort"
+    when "EDIT"  =~ re : puts "Action is edit"
+end
+#-----------------------------
+require 'abbrev'
+table = Abbrev.abbrev %w-send stop abort edit-
+loop do
+    print "Action: "
+    ans = $stdin.gets.chomp
+    puts "Action for #{ans} is #{table[ans.downcase]}"
+end
+
+
+#-----------------------------
+# dummy values are defined for 'file', 'PAGER', and
+# the 'invoke_editor' and 'deliver_message' methods
+# do not do anything interesting in this example.
+#!/usr/bin/ruby -w
+require 'abbrev'
+
+file = 'pleac_ruby.data'
+PAGER = 'less'
+
+def invoke_editor
+    puts "invoking editor"
+end
+
+def deliver_message
+    puts "delivering message"
+end
+
+actions = {
+    'edit'  => self.method(:invoke_editor),
+    'send'  => self.method(:deliver_message),
+    'list'  => proc {system(PAGER, file)},
+    'abort' => proc {puts "See ya!"; exit},
+    ""      => proc {puts "Unknown Command"}
+}
+
+dtable = Abbrev.abbrev(actions.keys)
+loop do
+    print "Action: "
+    ans = $stdin.gets.chomp.delete(" \t")
+    actions[ dtable[ans.downcase] || "" ].call
+end
+
+
+# @@PLEAC@@_6.19
+#-----------------------------
+# basically, the Perl Cookbook categorizes this as an
+# unsolvable problem ...
+#-----------------------------
+1 while addr.gsub!(/\([^()]*\)/,'')
+#-----------------------------
+Dear someuser@host.com,
+
+Please confirm the mail address you gave us Wed May  6 09:38:41
+MDT 1998 by replying to this message.  Include the string
+"Rumpelstiltskin" in that reply, but spelled in reverse; that is,
+start with "Nik...".  Once this is done, your confirmed address will
+be entered into our records.
+
+
+# @@PLEAC@@_6.21
+#-----------------------------
+#% gunzip -c ~/mail/archive.gz | urlify > archive.urlified
+#-----------------------------
+#% urlify ~/mail/*.inbox > ~/allmail.urlified
+#-----------------------------
+#!/usr/bin/ruby -w
+# urlify - wrap HTML links around URL-like constructs
+
+urls = '(https?|telnet|gopher|file|wais|ftp)';
+ltrs = '\w';
+gunk = '/#~:.?+=&%@!\-';
+punc = '.:?\-';
+any  = "#{ltrs}#{gunk}#{punc}";
+
+ARGF.each do |line|
+    line.gsub! %r/
+        \b                    # start at word boundary
+        (                     # begin $1  {
+         #{urls}     :        # need resource and a colon
+         [#{any}] +?          # followed by on or more
+                              #  of any valid character, but
+                              #  be conservative and take only
+                              #  what you need to....
+        )                     # end   $1  }
+        (?=                   # look-ahead non-consumptive assertion
+         [#{punc}]*           # either 0 or more punctuation
+         [^#{any}]            #   followed by a non-url char
+         |                    # or else
+         $                    #   then end of the string
+        )
+    /iox do 
+        %Q|<A HREF="#{$1}">#{$1}</A>|
+    end
+    print line
+end
+
+
+# @@PLEAC@@_6.23
+%r/^m*(d?c{0,3}|c[dm])(l?x{0,3}|x[lc])(v?i{0,3}|i[vx])$/i
+#-----------------------------
+str.sub!(/(\S+)(\s+)(\S+)/, '\3\2\1')
+#-----------------------------
+%r/(\w+)\s*=\s*(.*)\s*$/             # keyword is $1, value is $2
+#-----------------------------
+%r/.{80,}/
+#-----------------------------
+%r|(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+)|
+#-----------------------------
+str.gsub!(%r|/usr/bin|,'/usr/local/bin')
+#-----------------------------
+str.gsub!(/%([0-9A-Fa-f][0-9A-Fa-f])/){ $1.hex.chr }
+#-----------------------------
+str.gsub!(%r{
+    /\*                    # Match the opening delimiter
+    .*?                    # Match a minimal number of characters
+    \*/                    # Match the closing delimiter
+}xm,'')
+#-----------------------------
+str.sub!(/^\s+/, '')
+str.sub!(/\s+$/, '')
+
+# but really, in Ruby we'd just do:
+str.strip!
+#-----------------------------
+str.gsub!(/\\n/,"\n")
+#-----------------------------
+str.sub!(/^.*::/, '')
+#-----------------------------
+%r/^([01]?\d\d|2[0-4]\d|25[0-5])\.([01]?\d\d|2[0-4]\d|25[0-5])\.
+    ([01]?\d\d|2[0-4]\d|25[0-5])\.([01]?\d\d|2[0-4]\d|25[0-5])$/x
+#-----------------------------
+str.sub!(%r|^.*/|, '')
+#-----------------------------
+cols = ( (ENV['TERMCAP'] || " ") =~ /:co#(\d+):/ ) ? $1 : 80;
+#-----------------------------
+name = " #{$0} #{ARGV}".gsub(%r| /\S+/|, ' ')
+#-----------------------------
+require 'rbconfig'
+include Config
+raise "This isn't Linux" unless CONFIG['target_os'] =~ /linux/i;
+#-----------------------------
+str.gsub!(%r/\n\s+/, ' ')
+#-----------------------------
+nums = str.scan(/(\d+\.?\d*|\.\d+)/)
+#-----------------------------
+capwords = str.scan(%r/(\b[^\Wa-z0-9_]+\b)/)
+#-----------------------------
+lowords = str.scan(%r/(\b[^\WA-Z0-9_]+\b)/)
+#-----------------------------
+icwords = str.scan(%r/(\b[^\Wa-z0-9_][^\WA-Z0-9_]*\b)/)
+#-----------------------------
+links = str.scan(%r/<A[^>]+?HREF\s*=\s*["']?([^'" >]+?)[ '"]?>/mi)
+#-----------------------------
+initial = str =~ /^\S+\s+(\S)\S*\s+\S/ ? $1 : ""
+#-----------------------------
+str.gsub!(%r/"([^"]*)"/, %q-``\1''-)
+#-----------------------------
+
+$/ = ""
+sentences = []
+ARGF.each do |para|
+    para.gsub!(/\n/, ' ')
+    para.gsub!(/ {3,}/,'  ')
+    sentences << para.scan(/(\S.*?[!?.])(?=  |\Z)/)
+end
+
+#-----------------------------
+%r/(\d{4})-(\d\d)-(\d\d)/            # YYYY in $1, MM in $2, DD in $3
+#-----------------------------
+%r/ ^
+      (?:
+       1 \s (?: \d\d\d \s)?            # 1, or 1 and area code
+       |                               # ... or ...
+       \(\d\d\d\) \s                   # area code with parens
+       |                               # ... or ...
+       (?: \+\d\d?\d? \s)?             # optional +country code
+       \d\d\d ([\s\-])                 # and area code
+      )
+      \d\d\d (\s|\1)                   # prefix (and area code separator)
+      \d\d\d\d                         # exchange
+        $
+ /x
+#-----------------------------
+%r/\boh\s+my\s+gh?o(d(dess(es)?|s?)|odness|sh)\b/i
+#-----------------------------
+lines = []
+lines << $1 while input.sub!(/^([^\012\015]*)(\012\015?|\015\012?)/,'')
+
+
+# @@PLEAC@@_7.0
+# An IO object being Enumerable, we can use 'each' directly on it
+File.open("/usr/local/widgets/data").each { |line|
+    puts line if line =~ /blue/
+}
+
+logfile = File.new("/var/log/rubylog.txt", "w")
+mysub($stdin, logfile)
+
+# The method IO#readline is similar  to IO#gets
+# but throws an exception when it reaches EOF
+f = File.new("bla.txt")
+begin
+    while (line = f.readline)
+        line.chomp
+        $stdout.print line if line =~ /blue/
+    end
+rescue EOFError
+    f.close
+end
+
+while $stdin.gets                        # reads from STDIN
+    unless (/\d/) 
+        $stderr.puts "No digit found."   # writes to STDERR
+    end
+    puts "Read: #{$_}"                   # writes to STDOUT
+end
+
+logfile = File.new("/tmp/log", "w")
+
+logfile.close
+
+# $defout (or its synonym '$>') is the destination of output
+# for Kernel#print, Kernel#puts, and family functions
+logfile = File.new("log.txt", "w")
+old = $defout
+$defout = logfile                 # switch to logfile for output
+puts "Countdown initiated ..."
+$defout = old                     # return to original output
+puts "You have 30 seconds to reach minimum safety distance."
+
+
+# @@PLEAC@@_7.1
+source = File.new(path, "r")  # open file "path" for reading only
+sink   = File.new(path, "w")  # open file "path" for writing only
+
+source = File.open(path, File::RDONLY)  # open file "path" for reading only
+sink   = File.open(path, File::WRONLY)  # open file "path" for writing only
+
+file   = File.open(path, "r+")  # open "path" for reading and writing
+file   = File.open(path, flags) # open "path" with the flags "flags" (see examples below for flags)
+
+# open file "path" read only
+file   = File.open(path, "r")
+file   = File.open(path, File::RDONLY)
+
+# open file "path" write only, create it if it does not exist
+# truncate it to zero length if it exists
+file   = File.open(path, "w")
+file   = File.open(path, File::WRONLY|File::TRUNC|File::CREAT) 
+file   = File.open(path, File::WRONLY|File::TRUNC|File::CREAT, 0666)  # with permission 0666
+
+# open file "path" write only, fails if file exists
+file   = File.open(path, File::WRONLY|File::EXCL|File::CREAT) 
+file   = File.open(path, File::WRONLY|File::EXCL|File::CREAT, 0666) 
+
+# open file "path" for appending
+file   = File.open(path, "a")
+file   = File.open(path, File::WRONLY|File::APPEND|File::CREAT) 
+file   = File.open(path, File::WRONLY|File::APPEND|File::CREAT, 0666) 
+
+# open file "path" for appending only when file exists
+file   = File.open(path, File::WRONLY|File::APPEND) 
+
+# open file "path" for reading and writing
+file   = File.open(path, "r+")
+file   = File.open(path, File::RDWR)
+
+# open file for reading and writing, create a new file if it does not exist
+file   = File.open(path, File::RDWR|File::CREAT)
+file   = File.open(path, File::RDWR|File::CREAT, 0600)
+
+# open file "path" reading and writing, fails if file exists
+file   = File.open(path, File::RDWR|File::EXCL|File::CREAT)
+file   = File.open(path, File::RDWR|File::EXCL|File::CREAT, 0600)
+
+
+# @@PLEAC@@_7.2
+# No problem with Ruby since the filename doesn't contain characters with
+# special meaning; like Perl's sysopen
+File.open(filename, 'r')
+
+
+# @@PLEAC@@_7.3
+File.expand_path('~root/tmp')
+#=> "/root/tmp"
+File.expand_path('~rpcuser')
+#=> "/var/lib/nfs"
+
+# To expand ~/.. it explicitely needs the environment variable HOME
+File.expand_path('~/tmp')
+#=> "/home/gc/tmp"
+
+
+# @@PLEAC@@_7.4
+# The exception raised in Ruby reports the filename
+File.open('afile')
+
+
+# @@PLEAC@@_7.5
+# Standard Ruby distribution provides the following useful extension
+require 'tempfile'
+# With the Tempfile class, the file is automatically deleted on garbage
+# collection, so you won't need to remove it, later on.
+tf = Tempfile.new('tmp')   # a name is required to create the filename
+
+# If you need to pass the filename to an external program you can use
+# File#path, but don't forget to File#flush in order to flush anything
+# living in some buffer somewhere.
+tf.flush
+system("/usr/bin/dowhatever #{tf.path}")
+
+fh = Tempfile.new('tmp')
+fh.sync = true                # autoflushes
+10.times { |i| fh.puts i }
+fh.rewind
+puts 'Tmp file has: ', fh.readlines
+
+
+# @@PLEAC@@_7.6
+while (DATA.gets) do
+    # process the line  
+end
+__END__
+# your data goes here
+# __DATA__ doesn't exist in Ruby
+
+#CODE
+# get info about the script (size, date of last modification)
+kilosize = DATA.stat.size / 1024
+last_modif = DATA.stat.mtime
+puts "<P>Script size is #{kilosize}"
+puts "<P>Last script update: #{last_modif}"
+__END__
+# DO NOT REMOVE THE PRECEEDING LINE.
+# Everything else in this file will be ignored.
+#CODE
+
+
+# @@PLEAC@@_7.7
+while line = gets do
+    # do something with line.
+end
+
+#  or 
+while gets do
+    # do something with $_
+end
+
+# or more rubyish
+$stdin.each do |line|
+    # do stuff with line
+end
+
+
+# ARGF may makes this more easy
+# this is skipped if ARGV.size==0
+ARGV.each do |filename| 
+    # closing and exception handling are done by the block
+    open(filename) do |fd| 
+        fd.each do |line|
+            # do stuff with line
+        end   
+    end rescue abort("can't open %s" % filename)
+end
+
+# globbing is done in the Dir module
+ARGV = Dir["*.[Cch]"] if ARGV.empty?
+
+# note: optparse is the preferred way to handle this
+if (ARGV[0] == '-c')  
+    chop_first += 1
+    ARGV.shift
+end
+
+
+# processing numerical options
+if ARGV[0] =~ /^-(\d+)$/
+    columns = $1
+    ARGV.shift
+end
+
+# again, better to use optparse:
+require 'optparse'
+nostdout = 0
+append = 0
+unbuffer = 0
+ignore_ints = 0
+ARGV.options do |opt|
+    opt.on('-n') { nostdout +=1 }
+    opt.on('-a') { append   +=1 }
+    opt.on('-u') { unbuffer +=1 }
+    opt.on('-i') { ignore_ints +=1 }
+    opt.parse!
+end or abort("usage: " + __FILE__ + " [-ainu] [filenames]")
+
+# no need to do undef $/, we have File.read
+str = File.read(ARGV[0])
+
+# again we have File.read
+str = File.read(ARGV[0])
+
+# not sure what this should do:
+# I believe open the file, print filename, lineno and line:
+ARGF.each_with_index do |line, idx|
+    print ARGF.filename, ":", idx, ";", line
+end
+
+# print all the lines in every file passed via command line that contains login
+ARGF.each do |line|
+    puts line if line =~ /login/
+end
+#
+# even this would fit
+#%ruby -ne "print if /f/" 2.log
+#
+
+ARGF.each { |l| puts l.downcase! }
+
+#------------------
+#!/usr/bin/ruby -p
+# just like perl's -p
+$_.downcase!
+#
+
+# I don't know who should I trust. 
+# perl's version splits on \w+ while python's on \w.
+
+chunks = 0
+
+File.read(ARGV[0]).split.each do |word|
+    next if word =~ /^#/
+    break if ["__DATA__", "__END__"].member? word
+    chunks += 1 
+end
+
+print "Found ", chunks, " chunks\n"
+
+
+# @@PLEAC@@_7.8
+old = File.open(old_file)
+new = File.open(new_file, "w")
+while old.gets do
+    # change $_, then...
+    new.print $_
+end
+old.close
+new.close
+File.rename(old_file, "old.orig")
+File.rename(new_file, old_file)
+
+while old.gets do
+    if $. == 20 then # we are at the 20th line
+        new.puts "Extra line 1"
+        new.puts "Extra line 2"
+    end
+    new.print $_
+end
+
+while old.gets do
+    next if 20..30 # skip the 20th line to the 30th
+                   # Ruby (and Perl) permit to write if 20..30 
+                   # instead of if (20 <= $.) and ($. <= 30)
+    new.print $_
+end
+
+
+# @@PLEAC@@_7.9
+#% ruby -i.orig -pe 'FILTER COMMAND' file1 file2 file3 ...
+#
+#-----------------------------
+##!/usr/bin/ruby -i.orig -p
+# filter commands go here
+#-----------------------------
+
+#% ruby -pi.orig -e 'gsub!(/DATE/){Time.now)'
+
+# effectively becomes:
+ARGV << 'I'
+oldfile = ""
+while gets
+    if ARGF.filename != oldfile
+        newfile = ARGF.filename
+        File.rename(newfile, newfile + ".orig")
+        $stdout = File.open(newfile,'w')
+        oldfile = newfile
+    end
+    gsub!(/DATE/){Time.now}
+    print 
+end
+$stdout = STDOUT
+#-----------------------------
+#% ruby -i.old -pe 'gsub!(%r{\bhisvar\b}, 'hervar')' *.[Cchy]
+
+#-----------------------------
+# set up to iterate over the *.c files in the current directory,
+# editing in place and saving the old file with a .orig extension
+$-i = '.orig'                       # set up -i mode
+ARGV.replace(Dir['*.[Cchy]'])
+while gets
+    if $. == 1
+        print "This line should appear at the top of each file\n"
+    end
+    gsub!(/\b(p)earl\b/i, '\1erl')    # Correct typos, preserving case
+    print
+    ARGF.close if ARGF.eof
+end
+
+
+# @@PLEAC@@_7.10
+File.open('itest', 'r+') do |f|   # open file for update
+    lines = f.readlines           # read into array of lines
+    lines.each do |it|            # modify lines
+        it.gsub!(/foo/, 'QQQ')
+    end
+    f.pos = 0                     # back to start
+    f.print lines                 # write out modified lines
+    f.truncate(f.pos)             # truncate to new length
+end                               # file is automatically closed
+#-----------------------------
+File.open('itest', 'r+') do |f|   
+    out = ""
+    f.each do |line|
+        out << line.gsub(/DATE/) {Time.now}
+    end
+    f.pos = 0                     
+    f.print out
+    f.truncate(f.pos)             
+end
+
+# @@PLEAC@@_7.11
+File.open('infile', 'r+') do |f|
+    f.flock File::LOCK_EX
+    # update file
+end
+#-----------------------------
+File::LOCK_SH     # shared lock (for reading)
+File::LOCK_EX     # exclusive lock (for writing)
+File::LOCK_NB     # non-blocking request
+File::LOCK_UN     # free lock
+#-----------------------------
+unless f.flock File::LOCK_EX | File::LOCK_NB
+    warn "can't get immediate lock: blocking ..."
+    f.flock File::LOCK_EX 
+end
+#-----------------------------
+File.open('numfile', File::RDWR|File::CREAT) do |f|
+    f.flock(File::LOCK_EX)
+    num = f.gets.to_i || 0
+    f.pos = 0
+    f.truncate 0
+    f.puts num + 1q
+end
+
+
+# @@PLEAC@@_7.12
+output_handle.sync = true
+# Please note that like in Perl, $stderr is already unbuffered
+#-----------------------------
+#!/usr/bin/ruby -w
+# seeme - demo stdio output buffering
+$stdout.sync = ARGV.size > 0
+print "Now you don't see it..."
+sleep 2
+puts "now you do"
+#-----------------------------
+$stderr.sync = true
+afile.sync = false
+#-----------------------------
+# assume 'remote_con' is an interactive socket handle,
+# but 'disk_file' is a handle to a regular file.
+remote_con.sync = true       # unbuffer for clarity
+disk_file.sync = false       # buffered for speed
+#-----------------------------
+require 'socket'
+sock = TCPSocket.new('www.ruby-lang.org', 80)
+sock.sync = true
+sock.puts "GET /en/ HTTP/1.0 \n\n"
+resp = sock.read
+print "DOC IS: #{resp}\n"
+
+
+# @@PLEAC@@_7.13
+#-----------------------------
+# assumes fh1, fh2, fh2 are oen IO objects
+nfound = select([$stdin, fh1, fh2, fh3], nil, nil, 0)
+nfound[0].each do |file|
+    case file
+        when fh1
+            # do something with fh1
+        when fh2
+            # do something with fh2
+        when fh3
+            # do something with fh3
+    end
+end
+#-----------------------------
+input_files = []
+# repeat next line for all in-files to poll
+input_files << fh1
+if nfound = select(input_files, nil, nil, 0)
+    # input ready on files in nfound[0]
+end
+
+
+# @@PLEAC@@_8.0
+#-----------------------------
+# datafile is a file or IO object
+datafile.readlines.each { |line|
+    line.chomp!
+    size = line.length
+    puts size
+}
+#-----------------------------
+datafile.readlines.each { |line|
+    puts line.chomp!.length
+}
+#-----------------------------
+lines = datafile.readlines
+#-----------------------------
+whole_file = file.read
+#-----------------------------
+# ruby -040 -e 'word = gets; puts "First word is #{word}"'
+#-----------------------------
+# ruby -ne 'BEGIN { $/="%%\n" }; $_.chomp; puts $_ if( $_=~/Unix/i)' fortune.dat
+#-----------------------------
+handle.print "one", "two", "three" # "onetwothree"
+puts "Baa baa black sheep."        # sent to $stdout
+#-----------------------------
+buffer = handle.read(4096)
+rv     = buffer.length
+#-----------------------------
+handle.truncate(length)
+open("/tmp#{$$}.pid", 'w') { |handle| handle.truncate(length) }
+#-----------------------------
+pos = datafile.pos  # tell is an alias of pos
+puts "I'm #{pos} bytes from the start of datafile"
+#-----------------------------
+logfile.seek(0, IO::SEEK_END)
+datafile.seek(pos)  #  IO::SEEK_SET is the default
+out.seek(-20, IO::SEEK_CUR)
+#-----------------------------
+written = datafile.syswrite(mystring)
+raise RunTimeError unless written == mystring.length
+block = infile.sysread(256)   # no equivalent to perl offset parameter in sysread
+puts "only read #{block.length} bytes" if 256 != block.length
+#-----------------------------
+pos = handle.sysseek(0, IO::SEEK_CUR)  # don't change position
+
+
+# @@PLEAC@@_8.1
+while (line = fh.gets)
+    line.chomp!
+    nextline = nil
+    line.gsub!(/\\$/) { |match| nextline = fh.gets; '' }
+    if (nextline != nil)
+        line += nextline 
+        redo
+    end
+    # process full record in line here
+end
+#-----------------------------
+# DISTFILES = $(DIST_COMMON) $(SOURCES) $(HEADERS) \
+#         $(TEXINFOS) $(INFOS) $(MANS) $(DATA)
+# DEP_DISTFILES = $(DIST_COMMON) $(SOURCES) $(HEADERS) \
+#         $(TEXINFOS) $(INFO_DEPS) $(MANS) $(DATA) \
+#         $(EXTRA_DIST)
+#-----------------------------
+line.gsub!(/\\\s*$/, '') {
+    # as before
+}
+
+
+# @@PLEAC@@_8.2
+#-----------------------------
+count = `wc -l < #{filename}`
+fail "wc failed: #{$?}" if $? != 0
+count.chomp!
+#-----------------------------
+count = 0
+File.open(file, 'r') { |fh|
+    count += 1 while fh.gets
+}
+# count now holds the number of lines read
+#-----------------------------
+count = 0
+while (chunk = file.sysread(2**16)) 
+    count += chunk.count("\n")
+end rescue EOFError
+#-----------------------------
+File.open(filename,'r') { |fh|
+    count += 1 while fh.gets
+}
+# count now holds the number of lines read
+#-----------------------------
+# As ruby doesn't quite have an equivalent to using a for
+# statement as in perl, I threw this in
+count = File.readlines(filename).size
+#-----------------------------
+1 while file.gets
+count = $.
+#-----------------------------
+$/ = ''
+open(filename, 'r') { |fh|
+    1 while fh.gets
+    para_count = $.
+} rescue fail("can't open #{filename}: $!") 
+#-----------------------------
+
+
+# ^^PLEAC^^_8.3
+#-----------------------------
+while (gets)
+    split.each { |chunk|
+        # do something with chunk
+    }
+end
+#-----------------------------
+while (gets)
+    gsub(/(\w[\w'-]*)/) { |word|
+        # do something with word
+    }
+end
+#-----------------------------
+# Make a word frequency count
+# normally hashes can be created using {} or just Hash.new
+# but we want the default value of an entry to be 0 instead 
+# of nil. (nil can't be incremented)
+seen = Hash.new(0)
+while (gets)
+    gsub(/(\w[\w'-]*)/) { |word|
+        seen[word.downcase] += 1
+    }
+end
+# output hash in a descending numeric sort of its values
+seen.sort { |a,b| b[1] <=> a[1] }.each do |k,v|
+    printf("%5d %s\n", v, k )
+end
+
+#-----------------------------
+# Line frequency count
+seen = Hash.new(0)
+while (gets)
+    seen[$_.downcase] += 1
+end
+seen.sort { |a,b| b[1] <=> a[1] }.each do |k,v|
+    printf("%5d %s\n", v, k )
+end
+#-----------------------------
+
+
+# @@PLEAC@@_8.4
+#-----------------------------
+# instead of file handle FILE, we can just
+# use a string containing the filename
+File.readlines(file).each { |line|
+    # do something with line
+}
+#-----------------------------
+File.readlines(file).reverse_each { |line|
+    # do something with line
+}
+#-----------------------------
+# the variable lines might have been created
+# this way
+# lines = File.readlines(file)
+#
+# normally one would use the reverse_each, but
+# if you insist on using a numerical index to
+# iterate over the lines array...
+(lines.size - 1).downto(0) { |i|
+    line = lines[i]
+}
+#-----------------------------
+# the second readlines argument is a the 
+# record separator $/, just like perl, a blank
+# separator splits the records into paragraphs
+File.readlines(file, '').each { |paragraph|
+    # do something with paragraph
+    puts "->Paragraph #{paragraph}"
+}
+#-----------------------------
+
+
+# @@PLEAC@@_8.6
+
+$/ = "%\n";
+srand;
+
+File.open('/usr/share/fortune/humorists').each do |line|
+    adage = line if rand($.) < 1
+end
+
+puts adage;
+
+
+# @@PLEAC@@_8.10
+begin
+    fh = File.open(file, "r+")
+    addr = fh.tell unless fh.eof while fh.gets
+    fh.truncate(addr)
+rescue SystemCallError
+    $stderr.puts "#$!"
+end
+
+
+# @@PLEAC@@_9.0
+entry = File.stat("/usr/bin/vi")
+entry = File.stat("/usr/bin")
+entry = File.stat(INFILE)
+
+entry = File.stat("/usr/bin/vi")
+ctime = entry.ctime
+size  = entry.size
+
+f = File.open(filename, "r")
+
+## There is no -T equivalent in Ruby, but we can still test emptiness
+if test(?s, filename)
+  puts "#{filename} doesn't have text in it."
+  exit
+end
+
+Dir.new("/usr/bin").each do |filename|
+  puts "Inside /usr/bin is something called #{filename}"
+end
+
+
+# @@PLEAC@@_9.1
+file = File.stat("filename")
+readtime, writetime = file.atime, file.mtime
+file.utime(readtime, writetime)  
+
+SECONDS_PER_DAY = 60 * 60 * 24
+file = File.stat("filename")
+atime, mtime = file.atime, file.mtime
+
+atime -= 7 * SECONDS_PER_DAY
+mtime -= 7 * SECONDS_PER_DAY
+
+File.utime(atime, mtime, file)
+mtime = File.stat(file).mtime
+File.utime(Time.new, mtime, file)
+File.utime(Time.new, File.stat("testfile").mtime, file)
+
+#-----------------------------
+#!/usr/bin/ruby -w
+## uvi - vi a file without changing it's access times
+
+if ARGV.length != 1
+  puts "usage: uvi filename"
+  exit
+end
+file = ARGV[0]
+atime, mtime = File.stat(file).atime, File.stat(file).mtime
+system(ENV["EDITOR"] || "vi", file)
+File.utime(atime, mtime, file)
+#-----------------------------
+
+
+# @@PLEAC@@_9.2
+File.unlink(FILENAME)
+
+err_flg = false
+filenames.each do |file|
+  begin
+    File.unlink(file)
+  rescue
+    err_flg = $!
+  end
+end
+err_flg and raise "Couldn't unlink all of #{filenames.join(" ")}: #{err_flg}"
+
+File.unlink(file)
+
+count = filenames.length
+filenames.each do |file|
+  begin
+    File.unlink(file)
+  rescue
+    count -= 1
+  end
+end
+if count != filenames.length
+  STDERR.puts "could only delete #{count} of #{filenames.length} files"
+end
+
+
+# @@PLEAC@@_9.3
+require "ftools"
+File.copy(oldfile, newfile)
+
+infile  = File.open(oldfile, "r")
+outfile = File.open(newfile, "w")
+
+blksize = infile.stat.blksize
+# This doesn't handle partial writes or ^Z
+# like the Perl version does.
+while (line = infile.read(blksize))
+  outfile.write(line)
+end
+
+infile.close
+outfile.close
+
+system("cp #{oldfile} #{newfile}")    # unix
+system("copy #{oldfile} #{newfile}")  # dos, vms
+
+require "ftools"
+File.copy("datafile.dat", "datafile.bak")
+File.move("datafile.new", "datafile.dat")
+
+
+# @@PLEAC@@_9.4
+$seen = {} # must use global var to be seen inside of method below
+
+def do_my_thing(filename)
+    dev, ino = File.stat(filename).dev, File.stat(filename).ino
+    unless $seen[[dev, ino]]
+        # do something with $filename because we haven't
+        # seen it before
+    end
+    $seen[[dev, ino]] = $seen[[dev, ino]].to_i + 1
+end
+
+files.each do |filename|
+    dev, ino = File.stat(filename).dev, File.stat(filename).ino
+    if !$seen.has_key?([dev, ino])
+        $seen[[dev, ino]] = []
+    end
+    $seen[[dev, ino]].push(filename)
+end
+
+$seen.keys.sort.each do |devino|
+    ino, dev = devino
+    if $seen[devino].length > 1
+        # $seen[devino] is a list of filenames for the same file
+    end
+end
+
+
+# @@PLEAC@@_9.5
+Dir.open(dirname) do |dir|
+    dir.each do |file|
+        # do something with dirname/file
+        puts file
+    end
+end
+# Dir.close is automatic
+
+# No -T equivalent in Ruby
+
+dir.each do |file|
+    next if file =~ /^\.\.?$/
+    # ...
+end
+
+def plainfiles(dir)
+    dh = Dir.open(dir)
+    dh.entries.grep(/^[^.]/).
+        map      {|file| "#{dir}/#{file}"}.
+        find_all {|file| test(?f, file)}.
+        sort
+end
+
+
+# @@PLEAC@@_9.6
+list = Dir.glob("*.c")
+
+dir = Dir.open(path)
+files = dir.entries.grep(/\.c$/)
+dir.close
+
+files = Dir.glob("*.c")
+files = Dir.open(path).entries.grep(/\.[ch]$/i)
+
+dir = Dir.new(path)
+files = dir.entries.grep(/\.[ch]$/i)
+
+begin
+  d = Dir.open(dir)
+rescue Errno::ENOENT
+  raise "Couldn't open #{dir} for reading: #{$!}"
+end
+
+files = []
+d.each do |file|
+  puts file
+  next unless file =~ /\.[ch]$/i
+
+  filename = "#{dir}/#{file}"
+  # There is no -T equivalent in Ruby, but we can still test emptiness
+  files.push(filename) if test(?s, filename)
+end
+
+dirs.entries.grep(/^\d+$/).
+             map    { |file| [file, "#{path}/#{file}"]} .
+             select { |file| test(?d, file[1]) }.
+             sort   { |a,b|  a[0] <=> b[0] }.
+             map    { |file| file[1] }
+
+
+# @@PLEAC@@_9.7
+require 'find'
+Find.find(dirlist) do |file|
+  # do whatever
+end
+
+require 'find'
+argv = ARGV.empty? ? %w{.} : ARGV
+Find.find(*argv) do |file|
+  print file, (test(?d, file) ? "/\n" : "\n")
+end
+
+require 'find'
+argv = ARGV.empty? ? %w{.} : ARGV
+sum = 0
+Find.find(*argv) do |file|
+  size = test(?s, file) || 0
+  sum += size
+end
+puts "#{argv.join(' ')} contains #{sum} bytes"
+
+require 'find'
+argv = ARGV.empty? ? %w{.} : ARGV
+saved_size, saved_name = -1, ""
+Find.find(*argv) do |file|
+  size = test(?s, file) || 0
+  next unless test(?f, file) && size > saved_size
+  saved_size = size
+  saved_name = file
+end
+puts "Biggest file #{saved_name} in #{argv.join(' ')} is #{saved_size}"
+
+require 'find'
+argv = ARGV.empty? ? %w{.} : ARGV
+age, name = nil
+Find.find(*argv) do |file|
+  mtime = File.stat(file).mtime
+  next if age && age > mtime
+  age = mtime
+  name = file
+end
+puts "#{name} #{age}"
+
+#-----------------------------
+#!/usr/bin/ruby -w
+# fdirs - find all directories
+require 'find'
+argv = ARGV.empty? ? %w{.} : ARGV
+File.find(*argv) { |file| puts file if test(?d, file) }
+#-----------------------------
+
+
+# @@PLEAC@@_9.8
+require 'fileutils'
+
+puts "Usage #{$0} dir ..." if ARGV.empty?
+ARGV.each do |dir|
+  FileUtils.rmtree(dir)
+end
+
+
+# @@PLEAC@@_9.9
+require 'ftools'
+names.each do |file|
+  newname = file
+  begin
+    File.move(file, newname)
+  rescue Errno::EPERM
+    $stderr.puts "Couldn't rename #{file} to #{newname}: #{$!}"
+  end
+end
+
+require 'ftools'
+op = ARGV.empty? ? (raise "Usage: rename expr [files]\n") : ARGV.shift
+argv = ARGV.empty? ? $stdin.readlines.map { |f| f.chomp } : ARGV
+argv.each do |file|
+  was = file
+  file = eval("file.#{op}")
+  File.move(was, file) unless was == file
+end
+
+
+# @@PLEAC@@_9.10
+base = File.basename(path)
+dir  = File.dirname(path)
+# ruby has no fileparse equivalent
+dir, base = File.split(path)
+ext = base.scan(/\..*$/).to_s
+
+path = '/usr/lib/libc.a'
+file = File.basename(path)
+dir  = File.dirname(path)
+
+puts "dir is #{dir}, file is #{file}"
+# dir is /usr/lib, file is libc.a
+
+path = '/usr/lib/libc.a'
+dir, filename = File.split(path)
+name, ext = filename.split(/(?=\.)/)
+puts "dir is #{dir}, name is #{name}, ext is #{ext}"
+#   NOTE: The Ruby code prints
+#   dir is /usr/lib, name is libc, extension is .a
+#     while the Perl code prints a '/' after the directory name
+#   dir is /usr/lib/, name is libc, extension is .a
+
+# No fileparse_set_fstype() equivalent in ruby
+
+def extension(path)
+    ext = path.scan(/\..*$/).to_s
+    ext.sub(/^\./, "")
+end
+
+
+# @@PLEAC@@_9.11
+#-----------------------------
+#!/usr/bin/ruby -w
+# symirror - build spectral forest of symlinks
+
+require 'find'
+require 'fileutils'
+
+raise "usage: #{$0} realdir mirrordir" unless ARGV.size == 2
+
+srcdir,dstdir = ARGV
+srcmode = File::stat(srcdir).mode
+Dir.mkdir(dstdir, srcmode & 07777) unless test(?d, dstdir)
+
+# fix relative paths
+Dir.chdir(srcdir) {srcdir = Dir.pwd}
+Dir.chdir(dstdir) {dstdir = Dir.pwd}
+
+Find.find(srcdir) do |srcfile| 
+    if test(?d, srcfile)
+        dest = srcfile.sub(/^#{srcdir}/, dstdir)
+        dmode = File::stat(srcfile).mode & 07777
+        Dir.mkdir(dest, dmode) unless test(?d, dest)
+        a = Dir["#{srcfile}/*"].reject{|f| test(?d, f)}
+        FileUtils.ln_s(a, dest)
+    end
+end
+
+
+# @@PLEAC@@_9.12
+# we use the Getopt/Declare library here for convenience:
+#   http://raa.ruby-lang.org/project/getoptdeclare/
+#-----------------------------
+#!/usr/bin/ruby -w
+# lst - list sorted directory contents (depth first)
+
+require 'find'
+require 'etc'
+require "Getopt/Declare"
+
+# Note: in the option-spec below there must by at least one hard
+# tab in between each -option and its description. For example
+#    -i <tab> read from stdin
+
+opts = Getopt::Declare.new(<<'EOPARAM')
+    ============
+    Input Format:
+        -i	read from stdin
+    ============
+    Output Format:
+        -l	long listing
+        -r	reverse listing
+    ============
+    Sort on: (one of)
+        -m	mtime (modify time - default)
+                {$sort_criteria = :mtime}
+        -u	atime (access time)
+                {$sort_criteria = :atime}
+        -c	ctime (inode change time)
+                {$sort_criteria = :ctime}
+        -s	size
+                {$sort_criteria = :size}
+        [mutex: -m -u -c -s]
+
+EOPARAM
+
+$sort_criteria ||= :mtime
+files = {}
+DIRS = opts['-i'] ? $stdin.readlines.map{|f|f.chomp!} : ARGV
+DIRS.each do |dir|
+    Find.find(dir) do |ent|
+        files[ent] = File::stat(ent)
+    end
+end
+entries = files.keys.sort_by{|f| files[f].send($sort_criteria)}
+entries = entries.reverse unless opts['-r']
+
+entries.each do |ent|
+    unless opts['-l']
+        puts ent
+        next
+    end
+    stats = files[ent]
+    ftime = stats.send($sort_criteria == :size ? :mtime : $sort_criteria)
+    printf "%6d %04o %6d %8s %8s %8d %s %s\n",
+        stats.ino,
+        stats.mode & 07777,
+        stats.nlink,
+        ETC::PASSWD[stats.uid].name,
+        ETC::GROUP[stats.gid].name,
+        stats.size,
+        ftime.strftime("%a %b %d %H:%M:%S %Y"),
+        ent
+end
+
+
+# @@PLEAC@@_10.0
+def hello
+    $greeted += 1      # in Ruby, a variable beginning with $ is global (can be any type of course)
+    puts "hi there!"
+end
+
+# We need to initialize $greeted before it can be used, because "+=" is waiting a Numeric object
+$greeted = 0
+hello                  # note that appending () is optional to function calls with no parameters
+
+
+# @@PLEAC@@_10.1
+# In Ruby, parameters are named anyway
+def hypotenuse(side1, side2)
+    Math.sqrt(side1**2 + side2**2)    # the sqrt function comes from the Math module
+end
+diag = hypotenuse(3, 4)
+
+puts hypotenuse(3, 4)
+
+a = [3, 4]
+print hypotenuse(*a)                  # the star operator will magically convert an Array into a "tuple"
+
+both = men + women
+
+# In Ruby, all objects are references, so the same problem arises; we then return a new object
+nums = [1.4, 3.5, 6.7]
+def int_all(n)
+    n.collect { |v| v.to_i }
+end
+ints = int_all(nums)
+
+nums = [1.4, 3.5, 6.7]
+def trunc_em(n)
+    n.collect! { |v| v.to_i }         # the bang-version of collect modifies the object
+end
+trunc_em(nums)
+
+# Ruby has two chomp version:
+# ``chomp'' chomps the record separator and returns what's expected
+# ``chomp!'' does the same but also modifies the parameter object
+
+
+# @@PLEAC@@_10.2
+def somefunc
+    variable = something  # variable is local by default
+end
+
+name, age = ARGV
+start     = fetch_time
+
+a, b = pair               # will succeed if pair is an Array object (like ARGV is)
+c = fetch_time
+
+# In ruby, run_check can't access a, b, or c until they are
+# explicitely defined global (using leading $), even if they are
+# both defined in the same scope
+
+def check_x(x)
+    y = "whatever"
+    run_check
+    if $condition
+        puts "got $x"
+    end
+end
+
+# The following will keep a reference to the array, though the
+# results will be slightly different from perl: the last element
+# of $global_array will be itself an array
+def save_array(ary)
+    $global_array << ary
+end
+
+# The following gives the same results as in Perl for $global_array,
+# though it doesn't illustrate anymore the way to keep a reference
+# to an object: $global_array is extended with the elements of ary
+def save_array(ary)
+    $global_array += ary
+end
+
+
+# @@PLEAC@@_10.3
+# In Ruby, AFAIK a method cannot access "local variables" defined
+# upper scope; mostly because everything is an object, so you'll
+# do the same by defining an attribute or a static attribute
+
+# In Ruby the BEGIN also exists:
+BEGIN { puts "hello from BEGIN" }
+puts "hello from main"
+BEGIN { puts "hello from 2nd BEGIN" }
+# gives:
+#   hello from BEGIN
+#   hello from 2nd BEGIN
+#   hello from main
+
+# In Ruby, it can be written as a static method and a static
+# variable
+class Counter
+    @@counter = 0
+    def Counter.next_counter; @@counter += 1; end
+end
+
+# There is no need of BEGIN since the variable will get
+# initialized when parsing
+class Counter
+    @@counter = 42
+    def Counter.next_counter; @@counter += 1; end
+    def Counter.prev_counter; @@counter -= 1; end
+end
+
+
+# @@PLEAC@@_10.4
+# You can either get the whole trace as an array of strings, each
+# string telling which file, line and method is calling:
+caller
+
+# ...or only the last caller
+caller[0]
+
+# We need to extract just the method name of the backtrace:
+def whoami;  caller()[0] =~ /in `([^']+)'/ ? $1 : '(anonymous)'; end
+def whowasi; caller()[1] =~ /in `([^']+)'/ ? $1 : '(anonymous)'; end
+
+
+# @@PLEAC@@_10.5
+# In Ruby, every value is a reference on an object, thus there is
+# no such problem
+array_diff(array1, array2)
+
+def add_vecpair(a1, a2)
+    results = []
+    a1.each_index { |i| results << (a1[i] + a2[i]) }
+    results
+end
+a = [1, 2]
+b = [5, 8]
+c = add_vecpair(a, b)
+p c
+
+# Add this to the beginning of the function to check if we were
+# given two arrays
+a1.type == Array && a2.type == Array or
+    raise "usage: add_vecpair array1 array2 (was used with: #{a1.type} #{a2.type})"
+
+
+# @@PLEAC@@_10.6
+# There is no return context in Ruby
+
+
+# @@PLEAC@@_10.7
+# Like in Perl, we need to fake with a hash, but it's dirty :-(
+def thefunc(param_args)
+    args = { 'INCREMENT' => '10s', 'FINISH' => '0', 'START' => 0 }
+    args.update(param_args)
+    if (args['INCREMENT']  =~ /m$/ )
+        # .....
+    end
+end
+
+thefunc({ 'INCREMENT' => '20s', 'START' => '+5m', 'FINISH' => '+30m' })
+thefunc({})
+
+
+# @@PLEAC@@_10.8
+# there is no "undef" direct equivalent but there is the slice equiv:
+a, c = func.indexes(0, 2)
+
+
+# @@PLEAC@@_10.9
+# Ruby has no such limitation:
+def somefunc
+    ary = []
+    hash = {}
+    # ...
+    return ary, hash
+end
+arr, dict = somefunc
+
+array_of_hashes = fn
+h1, h2, h3      = fn
+
+
+# @@PLEAC@@_10.10
+return
+# or (equivalent)
+return nil
+
+
+# @@PLEAC@@_10.11
+# You can't prototype in Ruby regarding types :-(
+# Though, you can force the number of arguments:
+def func_with_no_arg; end
+def func_with_no_arg(); end
+def func_with_one_arg(a1); end
+def func_with_two_args(a1, a2); end
+def func_with_any_number_of_args(*args); end
+
+
+# @@PLEAC@@_10.12
+raise "some message"        # raise exception
+
+begin
+    val = func
+rescue Exception => msg
+    $stderr.puts "func raised an exception: #{msg}"
+end
+
+# In Ruby the rescue statement uses an exception class, every
+# exception which is not matched is still continuing
+begin
+    val = func
+rescue FullMoonError
+    ...
+end
+
+
+# @@PLEAC@@_10.13
+# Saving Global Values
+# Of course we can just save the value and restore it later:
+def print_age
+    puts "Age is #{$age}"
+end
+
+$age = 18         # global variable
+print_age()
+if condition
+    safeage = $age
+    $age = 23
+    print_age()
+    $age = safeage
+end
+
+# We can also use a method that saves the global variable and
+# restores it automatically when the block is left:
+
+def local(var)
+    eval("save = #{var.id2name}")
+    begin
+        result = yield
+    ensure
+        # we want to call this even if we got an exception
+        eval("#{var.id2name} = save")
+    end
+    result
+end
+
+condition = true
+$age = 18
+print_age()
+if condition
+    local(:$age) {
+        $age = 23
+        print_age()
+    }
+end
+print_age()
+
+# There is no need to use local() for filehandles or directory
+# handles in ruby because filehandles are normal objects.
+
+
+# @@PLEAC@@_10.14
+# In Ruby you may redefine a method [but not overload it :-(]
+# just by defining again with the same name.
+def foo; puts 'foo'; end
+def foo; puts 'bar'; end
+foo
+#=> bar
+
+# You can also take a reference to an existing method before
+# redefining a new one, using the `alias' keyword
+def foo; puts 'foo'; end
+alias foo_orig foo
+def foo; puts 'bar'; end
+foo_orig
+foo
+#=> foo
+#=> bar
+
+# AFAIK, there is no direct way to create a new method whose name
+# comes from a variable, so use "eval"
+colors = %w(red blue green yellow orange purple violet)
+colors.each { |c|
+    eval <<-EOS
+    def #{c}(*a)
+        "<FONT COLOR='#{c}'>" + a.to_s + "</FONT>"
+    end
+    EOS
+} 
+
+
+# @@PLEAC@@_10.15
+def method_missing(name, *args)
+    "<FONT COLOR='#{name}'>" + args.join(' ') + "</FONT>"
+end
+puts chartreuse("stuff")
+
+
+# @@PLEAC@@_10.16
+def outer(arg)
+    x = arg + 35
+    inner = proc { x * 19 }
+    x + inner.call()
+end
+
+
+# @@PLEAC@@_10.17
+#!/usr/bin/ruby -w
+# mailsort - sort mbox by different criteria
+require 'English'
+require 'Date'
+
+# Objects of class Mail represent a single mail.
+class Mail
+    attr_accessor :no
+    attr_accessor :subject
+    attr_accessor :fulltext
+    attr_accessor :date
+
+    def initialize
+        @fulltext = ""
+        @subject = ""
+    end
+
+    def append(para)
+        @fulltext << para
+    end
+
+    # this is called if you call puts(mail)
+    def to_s
+        @fulltext
+    end
+end
+
+# represents a list of mails.
+class Mailbox < Array
+
+    Subjectpattern = Regexp.new('Subject:\s*(?:Re:\s*)*(.*)\n')
+    Datepattern = Regexp.new('Date:\s*(.*)\n')
+
+    # reads mails from open file and stores them
+    def read(file)
+        $INPUT_RECORD_SEPARATOR = ''  # paragraph reads
+        msgno = -1
+        file.each { |para|
+            if para =~ /^From/
+                mail = Mail.new
+                mail.no = (msgno += 1)
+                md = Subjectpattern.match(para)
+                if md
+                    mail.subject = md[1]
+                end
+                md = Datepattern.match(para)
+                if md
+                    mail.date = DateTime.parse(md[1])
+                else
+                    mail.date = DateTime.now
+                end
+                self.push(mail)
+            end
+            mail.append(para) if mail
+        }
+    end
+
+    def sort_by_subject_and_no
+        self.sort_by { |m|
+            [m.subject, m.no]
+        }
+    end
+
+    # sorts by a list of attributs of mail, given as symbols
+    def sort_by_attributs(*attrs)
+        # you can sort an Enumerable by an array of
+        # values, they would be compared
+        # from ary[0] to ary[n]t, say:
+        # ['b',1] > ['a',10] > ['a',9]
+        self.sort_by { |elem|
+            attrs.map { |attr|
+                elem.send(attr)
+            }
+        }
+    end
+
+end
+
+mailbox = Mailbox.new
+mailbox.read(ARGF)
+
+# print only subjects sorted by subject and number
+for m in mailbox.sort_by_subject_and_no
+    puts(m.subject)
+end
+
+# print complete mails sorted by date, then subject, then number
+for m in mailbox.sort_by_attributs(:date, :subject)
+    puts(m)
+end
+
+
+# @@PLEAC@@_11.7
+def mkcounter(count)
+    start  = count 
+    bundle = { 
+        "NEXT"   => proc { count += 1 },
+        "PREV"   => proc { count -= 1 },
+        "RESET"  => proc { count = start }
+    }
+    bundle["LAST"] = bundle["PREV"]
+    return bundle
+end
+
+c1 = mkcounter(20)
+c2 = mkcounter(77)
+
+puts "next c1: #{c1["NEXT"].call}"  # 21 
+puts "next c2: #{c2["NEXT"].call}"  # 78 
+puts "next c1: #{c1["NEXT"].call}"  # 22 
+puts "last c1: #{c1["PREV"].call}"  # 21 
+puts "last c1: #{c1["LAST"].call}"  # 20 
+puts "old  c2: #{c2["RESET"].call}" # 77 
+
+
+# @@PLEAC@@_11.15
+class Binary_tree
+    def initialize(val)
+        @value = val
+        @left = nil
+        @right = nil
+    end
+    
+    # insert given value into proper point of
+    # provided tree.  If no tree provided, 
+    # use implicit pass by reference aspect of @_
+    # to fill one in for our caller.
+    def insert(val)
+        if val < @value then
+            if @left then
+                @left.insert(val)
+            else
+                @left = Binary_tree.new(val)
+            end
+        elsif val > @value then
+            if @right then
+                @right.insert(val)
+            else
+                @right = Binary_tree.new(val)
+            end
+        else
+            puts "double"
+            # do nothing, no double values
+        end
+    end
+
+    # recurse on left child, 
+    # then show current value, 
+    # then recurse on right child.  
+    def in_order
+        @left.in_order if @left
+        print @value, " "
+        @right.in_order if @right
+    end
+    
+    # show current value, 
+    # then recurse on left child, 
+    # then recurse on right child.
+    def pre_order
+        print @value, " "
+        @left.pre_order if @left
+        @right.pre_order if @right
+    end
+
+    # recurse on left child, 
+    # then recurse on right child,
+    # then show current value.
+    def post_order
+        @left.post_order if @left
+        @right.post_order if @right
+        print @value, " "
+    end
+
+    # find out whether provided value is in the tree.
+    # if so, return the node at which the value was found.
+    # cut down search time by only looking in the correct
+    # branch, based on current value.
+    def search(val)
+        if val == @value then
+            return self
+        elsif val < @value then
+            return @left.search(val) if @left
+            return nil
+        else
+            return @right.search(val) if @right
+            return nil
+        end
+    end
+end
+
+# first generate 20 random inserts
+test = Binary_tree.new(0)
+for a in 0..20
+    test.insert(rand(1000)) 
+end
+
+# now dump out the tree all three ways
+print "Pre order:  ";  test.pre_order;  puts ""
+print "In order:  ";  test.in_order;  puts ""
+print "Post order:  ";  test.post_order;  puts ""
+
+print "search?"
+while gets
+    print test.search($_.to_i)
+    print "\nsearch?"
+end
+
+
+# @@PLEAC@@_12.0
+# class and module names need to have the first letter capitalized
+module Alpha
+    NAME = 'first'
+end
+module Omega
+    NAME = 'last'
+end
+puts "Alpha is #{Alpha::NAME}, Omega is #{Omega::NAME}"
+
+# ruby doesn't differentiate beteen compile-time and run-time
+require 'getoptlong.rb'
+require 'getoptlong'     # assumes the .rb
+require 'cards/poker.rb'
+require 'cards/poker'    # assumes the .rb
+load    'cards/poker'    # require only loads the file once
+
+module Cards
+    module Poker
+        @card_deck = Array.new # or @card_deck = []
+        def shuffle
+        end
+    end
+end
+
+
+# @@PLEAC@@_12.1
+# a module exports all of its functions
+module Your_Module
+    def self.function
+        # this would be called as Your_Module.function
+    end
+    
+    def Your_Module.another
+        # this is the same as above, but more specific
+    end
+end
+
+# @@PLEAC@@_12.2
+begin
+    require 'nonexistent'
+rescue LoadError
+    puts "Couldn't load #{$!}"  # $! contains the last error string
+end
+
+# @@PLEAC@@_12.4
+# module variables are private unless access functions are defined
+module Alpha
+    @aa = 10
+    @bb = 11
+    
+    def self.put_aa
+        puts @aa
+    end
+    
+    def self.bb=(val)
+        @bb = val
+    end
+end
+
+Alpha.bb = 12
+# Alpha.aa = 10 # error, no aa=method
+
+
+# @@PLEAC@@_12.5
+# caller provides a backtrace of the call stack
+module MyModule
+    def find_caller
+        caller
+    end
+
+    def find_caller2(i)
+        caller(i) # an argument limits the size of the stack returned
+    end
+end
+
+
+# @@PLEAC@@_12.6
+BEGIN {
+    $logfile = '/tmp/mylog' unless defined? $logfile
+    $LF = File.open($logfile, 'a')
+}
+
+module Logger
+    def self.logmsg(msg)
+        $LF.puts msg
+    end
+
+    logmsg('startup')
+end
+
+END {
+    Logger::logmsg('shutdown')
+    $LF.close
+}
+
+
+# @@PLEAC@@_12.7
+#-----------------------------
+# results may be different on your system
+# % ruby -e "$LOAD_PATH.each_index { |i| printf("%d %s\n", i, $LOAD_PATH[i] }
+#0 /usr/local/lib/site_ruby/1.6
+#1 /usr/local/lib/site_ruby/1.6/i386-linux
+#2 /usr/local/lib/site_ruby/
+#3 /usr/lib/ruby/1.6
+#4 /usr/lib/ruby/1.6/i136-linux
+#5 .
+#-----------------------------
+# syntax for sh, bash, ksh, or zsh
+#$ export RUBYLIB=$HOME/rubylib
+
+# syntax for csh or tcsh
+# % setenv RUBYLIB ~/rubylib
+#-----------------------------
+$LOAD_PATH.unshift "/projects/spectre/lib";
+
+
+# @@PLEAC@@_12.8
+# equivalents in ruby are mkmf, SWIG, or Ruby/DL depending on usage
+
+
+# @@PLEAC@@_12.9
+# no equivalent in ruby
+
+
+# @@PLEAC@@_12.10
+# no equivalent in ruby
+
+
+# @@PLEAC@@_12.11
+module FineTime
+    def self.time
+        # to be defined later
+    end
+end
+
+
+module FineTime
+    def self.time
+        "its a fine time"
+    end
+end
+
+puts FineTime.time #=> "its a fine time"
+
+
+# @@PLEAC@@_12.12
+def even_only(n)
+    raise "#{n} is not even" if (n & 1) != 0  # one way to test
+    # ...
+end
+def even_only(n)
+    $stderr.puts "#{n} is not even" if (n & 1) != 0
+    # ...
+end
+
+
+# @@PLEAC@@_12.17
+# The library archive for ruby is called Ruby Application archive,
+# or shorter RAA, and can be found at http://raa.ruby-lang.org.
+# A typical library is installed like this:
+# % gunzip some-module-4.54.tar.gz
+# % tar xf some-module-4.54.tar
+# % cd some-module-4.54.tar
+# % ruby install.rb config
+# % ruby install.rb setup
+# get superuser previleges here if needed for next step
+# % ruby install.rb install
+
+# Some modules use a different process,
+# you should find details in the documentation
+# Here is an example of such a different process
+# % ruby extconf.rb
+# % make
+# % make install
+
+# If you want the module installed in your own directory:
+# For ruby version specific libraries
+# % ruby install.rb config --site-ruby=~/lib
+# For version independent libraries
+# % ruby install.rb config --site-ruby-common=~/lib
+
+# Information about possible options for config
+# % ruby install.rb --help
+
+# If you have your own complete distribution
+# % ruby install.rb --prefix=path=~/ruby-private
+
+
+# @@PLEAC@@_13.0
+# Classes and objects in Ruby are rather straigthforward
+class Person
+    # Class variables (also called static attributes) are prefixed by @@
+    @@person_counter=0
+    
+    # object constructor
+    def initialize(age, name, alive = true)     # Default arg like in C++
+        @age, @name, @alive = age, name, alive  # Object attributes are prefixed by '@'
+        @@person_counter += 1
+          # There is no '++' operator in Ruby. The '++'/'--'  operators are in fact 
+          # hidden assignments which affect variables, not objects. You cannot accomplish
+          # assignment via method. Since everything in Ruby is object, '++' and '--' 
+          # contradict Ruby OO ideology. Instead '-=' and '+=' are used.
+    end
+    
+    attr_accessor :name, :age   # This creates setter and getter methods for @name
+                                # and @age. See 13.3 for detailes.
+    
+    # methods modifying the receiver object usually have the '!' suffix
+    def die!
+        @alive = false
+        puts "#{@name} has died at the age of #{@age}."
+        @alive
+    end
+    
+    def kill(anotherPerson)
+        print @name, ' is killing ', anotherPerson.name, ".\n"
+        anotherPerson.die!
+    end
+
+    # methods used as queries
+    # usually have the '?' suffix    
+    def alive?
+        @alive && true
+    end
+    
+    def year_of_birth
+        Time.now.year - @age
+    end
+    
+    # Class method (also called static method)
+    def Person.number_of_people
+        @@person_counter
+    end
+end
+
+# Using the class:
+# Create objects of class Person
+lecter = Person.new(47, 'Hannibal')
+starling = Person.new(29, 'Clarice', true)
+pazzi = Person.new(40, 'Rinaldo', true)
+
+# Calling a class method
+print "There are ", Person.number_of_people, " Person objects\n"
+
+print pazzi.name, ' is ', (pazzi.alive?) ? 'alive' : 'dead', ".\n"
+lecter.kill(pazzi)
+print pazzi.name, ' is ', (pazzi.alive?) ? 'alive' : 'dead', ".\n"
+
+print starling.name , ' was born in ', starling.year_of_birth, "\n"
+
+
+# @@PLEAC@@_13.1
+# If you don't need any initialisation in the constructor,
+# you don't need to write a constructor.
+class MyClass
+end
+
+class MyClass
+    def initialize
+        @start = Time.new
+        @age = 0
+    end
+end
+
+class MyClass
+    def initialize(inithash)
+        @start = Time.new
+        @age = 0
+        for key, value in inithash
+            instance_variable_set("@#{key}", value)
+        end
+    end
+end
+
+# @@PLEAC@@_13.2
+# Objects are destroyed by the garbage collector.
+# The time of destroying is not predictable.
+# The ruby garbage collector can handle circular references,
+# so there is no need to write destructor for that.
+
+# There is no direct support for destructor.
+# You can call a custom function, or more specific a proc object, when the
+# garbage collector is about to destruct the object, but it is unpredictable
+# when this occurs.
+# Also if such a finalizer object has a reference to the orignal object,
+# this may prevent the original object to get garbage collected.
+# Because of this problem the finalize method below is
+# a class method and not a instance method.
+# So if you need to free resources for an object, like
+# closing a socket or kill a spawned subprocess,
+# you should do it explicitly.
+
+class MyClass
+    def initialize
+        ObjectSpace.define_finalizer(self,
+                                     self.class.method(:finalize).to_proc)
+    end
+    def MyClass.finalize(id)
+        puts "Object #{id} dying at #{Time.new}"
+    end
+end
+
+# test code
+3.times {
+    MyClass.new
+}
+ObjectSpace.garbage_collect
+
+
+# @@PLEAC@@_13.3
+# You can write getter and setter methods in a natural way:
+class Person
+    def name
+        @name
+    end
+    def name=(name)
+        @name = name
+    end
+end
+
+# But there is a better and shorter way
+class Person
+    attr_reader :age
+    attr_writer :name  
+    # attr_reader and attr_writer are actually methods in class Class
+    # which set getter and setter methods for you.
+end
+
+# There is also attr_accessor to create both setters and getters
+class Person
+    attr_accessor :age, :name
+end
+
+
+# @@PLEAC@@_13.4
+class Person
+    # Class variables (also called static attributes) are prefixed by @@
+    @@person_counter = 0
+    
+    def Person.population
+        @@person_counter
+    end
+    def initialize
+        @@person_counter += 1
+        ObjectSpace.define_finalizer(self,
+                                     self.class.method(:finalize).to_proc)
+    end
+    def Person.finalize(id)
+        @@person_counter -= 1
+    end
+end
+people = []
+10.times {
+    people.push(Person.new)
+}
+printf("There are %d people alive", Person.population)
+
+
+FixedArray.class_max_bounds = 100
+alpha = FixedArray.new
+puts "Bound on alpha is #{alpha.max_bounds}"
+
+beta = FixedArray.new
+beta.max_bounds = 50                    # calls the instance method
+beta.class.class_max_bounds = 50        # alternative, calls the class method
+puts "Bound on alpha is #{alpha.max_bounds}"
+    
+class FixedArray
+    @@bounds = 7
+    
+    def max_bounds
+        @@max_bounds
+    end
+    # instance method, which sets the class variable
+    def max_bounds=(value)
+        @@max_bounds = value
+    end
+    # class method. This can only be called on a class,
+    # but not on the instances
+    def FixedArray.class_max_bounds=(value)
+        @@max_bounds = value
+    end
+end
+
+
+# @@PLEAC@@_13.5
+PersonStruct = Struct.new("Person", :name, :age, :peers)
+# creates a class "Person::Struct", which is accessiable with the
+# constant "PersonStruct"
+p = PersonStruct.new
+p = Struct::Person.new                      # alternative using the classname
+p.name = "Jason Smythe"
+p.age = 13
+p.peers = ["Wilbur", "Ralph", "Fred"]
+p[:peers] = ["Wilbur", "Ralph", "Fred"]     # alternative access using symbol
+p["peers"] = ["Wilbur", "Ralph", "Fred"]    # alternative access using name of field
+p[2] = ["Wilbur", "Ralph", "Fred"]          # alternative access using index of field
+puts "At age #{p.age}, #{p.name}'s first friend is #{p.peers[0]}"
+
+# The fields of a struct have no special type, like other ruby variables
+# you can put any objects in. Therefore the discussions how to specify
+# the types of the fields do not apply to ruby.
+
+FamilyStruct = Struct.new("Family", :head, :address, :members)
+folks = FamilyStruct.new
+folks.head = PersonStruct.new
+dad = folks.head
+dad.name = "John"
+dad.age = 34
+
+# supply of own accessor method for the struct for error checking
+class PersonStruct
+    def age=(value)
+        if !value.kind_of?(Integer)
+            raise(ArgumentError, "Age #{value} isn't an Integer")
+        elsif value > 150
+            raise(ArgumentError, "Age #{value} is unreasonable")
+        end
+        @age = value
+    end
+end
+
+
+# @@PLEAC@@_13.6
+# The ruby Object class defines a dup and a clone method.
+# The dup method is recommended for prototype object creation.
+# The default implementation makes a shallow copy,
+# but each class can override it, for example to make a deep copy.
+
+# If you want to call 'new' directly on the instances,
+# you can create a instance method "new", which returns a new duplicate.
+# This method is distinct from the class method new.
+#
+class A
+    def new
+        dup
+    end
+end
+
+ob1 = A.new
+# later on
+ob2 = ob1.new
+
+
+# @@PLEAC@@_13.7
+methname = 'flicker'
+obj.send(methname, 10)      # calls obj.flicker(10)
+
+# call three methods on the object, by name
+['start', 'run', 'stop'].each do |method_string|
+    obj.send(method_string)
+end
+
+# Another way is to create a Method object
+method_obj = obj.method('flicker')
+# And then call it
+method_obj.call(10)
+
+
+# @@PLEAC@@_13.8
+# All classes in Ruby inherit from class Object
+# and thus all objects share methods defined in this class
+
+# the class of the object
+puts any_object.type
+
+# Ruby classes are actually objects of class Class and they
+# respond to methods defined in Object class as well
+
+# the superclass of this class
+puts any_object.class.superclass
+
+# ask an object whether it is an instance of particular class
+n = 4.7
+puts n.instance_of?(Float)    # true
+puts n.instance_of?(Numeric)  # false
+
+# ask an object whether it is an instance of class, one of the
+# superclasses of the object, or modules included in it
+puts n.kind_of?(Float)       # true (the class)
+puts n.kind_of?(Numeric)     # true (an ancestor class)
+puts n.kind_of?(Comparable)  # true (a mixin module)
+puts n.kind_of?(String)      # false
+
+# ask an object whether it can respond to a particular method
+puts n.respond_to?('+')      # true
+puts n.respond_to?('length') # false
+
+# all methods an object can respond to
+'just a string'.methods.each { |m| puts m }
+
+
+# @@PLEAC@@_13.9
+# Actually any class in Ruby is inheritable
+class Person        
+    attr_accessor :age, :name
+    def initialize
+        @name
+        @age
+    end
+end
+#-----------------------------
+dude = Person.new
+dude.name = 'Jason'
+dude.age = 23
+printf "%s is age %d.\n", dude.name, dude.age
+#-----------------------------
+# Inheriting from Person
+class Employee < Person
+    attr_accessor :salary
+end
+#-----------------------------
+empl = Employee.new
+empl.name = 'Jason'
+empl.age = 23
+empl.salary = 200
+printf "%s is age %d, the salary is %d.\n", empl.name, empl.age, empl.salary
+#-----------------------------
+# Any built-in class can be inherited the same way
+class WeirdString < String  
+    def initialize(obj)
+        super obj
+    end
+    def +(anotherObj)   # + method in this class is overridden
+        # to return the sum of string lengths
+        self.length + anotherObj.length  # 'self' can be omitted
+    end  
+end
+#-----------------------------
+a = WeirdString.new('hello')
+b = WeirdString.new('bye')
+
+puts a + b    # the overridden +
+#=> 8
+puts a.length # method from the superclass, String
+#=> 5
+
+
+# @@PLEAC@@_13.11
+# In ruby you can override the method_missing method
+# to have a solution similar to perls AUTOLOAD.
+class Person
+
+    def initialize
+        @ok_fields = %w(name age peers parent)
+    end
+
+    def valid_attribute?(name)
+        @ok_fields.include?(name)
+    end
+
+    def method_missing(namesymbol, *params)
+        name = namesymbol.to_s
+        return if name =~ /^A-Z/
+        if name.to_s[-1] == ('='[0])       # we have a setter
+            isSetter = true
+            name.sub!(/=$/, '')
+        end
+        if valid_attribute?(name)
+            if isSetter
+                instance_variable_set("@#{name}", *params)
+            else
+                instance_variable_get("@#{name}", *params)
+            end
+        else
+            # if no annestor is responsible,
+            # the Object class will throw a NoMethodError exception
+            super(namesymbol, *params)
+        end
+    end
+
+    def new
+        kid = Person.new
+        kid.parent = self
+        kid
+    end
+
+end
+
+dad = Person.new
+dad.name = "Jason"
+dad.age = 23
+kid = dad.new
+kid.name = "Rachel"
+kid.age = 2
+puts "Kid's parent is #{kid.parent.name}"
+puts dad
+puts kid
+
+class Employee < Person
+    def initialize
+        super
+        @ok_fields.push("salary", "boss")
+    end
+    def ok_fields
+        @ok_fields
+    end
+end
+
+
+# @@PLEAC@@_13.13
+# The ruby garbage collector pretends to cope with circular structures.
+# You can test it with this code:
+class RingNode
+    attr_accessor :next
+    attr_accessor :prev
+    attr_reader :name
+
+    def initialize(aName)
+        @name = aName
+        ObjectSpace.define_finalizer(self,
+                                     self.class.method(:finalize).to_proc)
+    end
+
+    def RingNode.finalize(id)
+        puts "Node #{id} dying"
+    end
+
+    def RingNode.show_all_objects
+        ObjectSpace.each_object {|id|
+            puts id.name if id.class == RingNode
+        }
+    end
+end
+
+def create_test
+    a = RingNode.new("Node A")
+    b = RingNode.new("Node B")
+    c = RingNode.new("Node C")
+    a.next = b
+    b.next = c
+    c.next = a
+    a.prev = c
+    c.prev = b
+    b.prev = a
+
+    a = nil
+    b = nil
+    c = nil
+end
+
+create_test
+RingNode.show_all_objects
+ObjectSpace.garbage_collect
+puts "After garbage collection"
+RingNode.show_all_objects
+
+
+# @@PLEAC@@_13.14
+class String
+    def <=>(other)
+        self.casecmp other
+    end
+end
+
+# There is no way to directly overload the '""' (stringify) 
+# operator in Ruby.  However, by convention, classes which 
+# can reasonably be converted to a String will define a 
+# 'to_s' method as in the TimeNumber class defined below.
+# The 'puts' method will automatcally call an object's
+# 'to_s' method as is demonstrated below.
+# Furthermore, if a class defines a to_str method, an object of that
+# class can be used most any place where the interpreter is looking 
+# for a String value.
+
+#---------------------------------------
+# NOTE: Ruby has a builtin Time class which would usually be used 
+# to manipulate time objects, the following is supplied for
+# educational purposes to demonstrate operator overloading.
+#
+class TimeNumber
+    attr_accessor  :hours,:minutes,:seconds
+    def initialize( hours, minutes, seconds)
+        @hours = hours
+        @minutes = minutes
+        @seconds = seconds
+    end
+    
+    def to_s
+        return sprintf( "%d:%02d:%02d", @hours, @minutes, @seconds)
+    end
+
+    def to_str
+        to_s
+    end
+
+    def +( other)
+        seconds = @seconds + other.seconds
+        minutes = @minutes + other.minutes
+        hours = @hours + other.hours
+        if seconds >= 60
+            seconds %= 60
+            minutes += 1
+        end
+        if minutes >= 60
+            minutes %= 60
+            hours += 1
+        end
+        return TimeNumber.new(hours, minutes, seconds)
+    end
+
+    def -(other)
+        raise NotImplementedError
+    end
+
+    def *(other)
+        raise NotImplementedError
+    end
+
+    def /( other)
+        raise NotImplementedError
+    end
+end
+
+t1 = TimeNumber.new(0, 58, 59)
+sec = TimeNumber.new(0, 0, 1)
+min = TimeNumber.new(0, 1, 0)
+puts t1 + sec + min + min
+
+#-----------------------------
+# StrNum class example: Ruby's builtin String class already has the 
+# capabilities outlined in StrNum Perl example, however the '*' operator
+# on Ruby's String class acts differently: It creates a string which
+# is the original string repeated N times.
+#
+# Using Ruby's String class as is in this example:
+x = "Red"; y = "Black"
+z = x+y
+r = z*3 # r is "RedBlackRedBlackRedBlack"
+puts "values are #{x}, #{y}, #{z}, and #{r}"
+print "#{x} is ", x < y ? "LT" : "GE", " #{y}\n"
+# prints:
+# values are Red, Black, RedBlack, and RedBlackRedBlackRedBlack
+# Red is GE Black
+
+#-----------------------------
+class FixNum
+    REGEX = /(\.\d*)/
+    DEFAULT_PLACES = 0
+    attr_accessor :value, :places
+    def initialize(value, places = nil)
+        @value = value
+        if places
+            @places = places
+        else
+            m = REGEX.match(value.to_s) 
+            if m
+                @places = m[0].length - 1
+            else
+                @places = DEFAULT_PLACES
+            end
+        end
+    end
+
+    def +(other)
+        FixNum.new(@value + other.value, max(@places, other.places))
+    end
+
+    def *(other)
+        FixNum.new(@value * other.value, max(@places, other.places))
+    end
+
+    def /(other)
+        puts "Divide: #{@value.to_f/other.value.to_f}"
+        result = FixNum.new(@value.to_f/other.value.to_f)
+        result.places = max(result.places,other.places) 
+        result
+    end
+
+    def to_s
+        sprintf("STR%s: %.*f", self.class.to_s , @places, @value)   #.
+    end  
+
+    def to_str
+        to_s
+    end
+
+    def to_i #convert to int
+        @value.to_i
+    end
+
+    def to_f #convert to float`
+        @value.to_f
+    end
+
+    private
+    def max(a,b)
+        a > b ? a : b
+    end
+end
+
+def demo()
+    x = FixNum.new(40)
+    y = FixNum.new(12, 0)
+
+    puts "sum of #{x} and #{y} is  #{x+y}"
+    puts "product of #{x} and #{y} is #{x*y}"
+
+    z = x/y
+    puts "#{z} has #{z.places} places"
+    unless z.places
+        z.places = 2
+    end
+
+    puts "div of #{x} by #{y} is #{z}"
+    puts "square of that is  #{z*z}"
+end
+
+if __FILE__ == $0
+    demo()
+end
+
+
+# @@PLEAC@@_14.1
+# There are dbm, sdbm, gdbm modules
+# and the bdb module for accessing the berkeley db
+# sdbm seem to be available on the most systems,
+# so we use it here
+#
+require "sdbm"
+SDBM.open("filename", 0666) { |dbobj|
+    # raises exception if open error
+    
+    # the returned sdbm-dbobj has most of the methods of a hash
+    v = dbobj["key"]
+    dbobj["key"] = "newvalue"
+    if dbobj.has_key?("key")
+        # ...
+    end
+    dbobj.delete("key2")
+}
+# database is open only inside the block.
+
+# It is also possible to use a open .. close pair:
+dbobj = SDBM.open("filename", 0666)
+#.. do something with dbobj
+dbobj.close
+
+#!/usr/bin/ruby -w
+# userstats - generate statistics on who is logged in
+# call with usernames as argument to display the totals
+# for the given usernames, call with "ALL" to display all users
+
+require "sdbm"
+filename = '/tmp/userstats.db'
+SDBM.open(filename, 0666) { |dbobj|
+    if ARGV.length > 0
+        if ARGV[0] == "ALL"
+            # ARGV is constant, so we need the variable userlist
+            userlist = dbobj.keys().sort()
+        else
+            userlist = ARGV
+        end
+        userlist.each { |user|
+            print "#{user}\t#{dbobj[user]}\n"
+        }
+    else
+        who = `who`
+        who.split("\n").each { |line|
+            md = /^(\S+)/.match(line)
+            raise "Bad line from who: #{line}" unless md
+            # sdbm stores only strings, so "+=" doesn't work,
+            # we need to convert them expicitly back to integer.
+            if dbobj.has_key?(md[0])
+                dbobj[md[0]] = dbobj[md[0]].to_i + 1
+            else
+                dbobj[md[0]] = "1"
+            end
+        }
+    end
+}
+
+
+# @@PLEAC@@_14.2
+# using open and clear
+dbobj = SDBM.open("filename", 0666)
+dbobj.clear()
+dbobj.close()
+# deleting file and recreating it
+# the filenames depend on the flavor of dbm you use,
+# for example sdbm has two files named filename.pag and filename.dir,
+# so you need to delete both files
+begin
+    File.delete("filename")
+    # raises Exception if not exist
+    dbobj = SDBM.open("filename", 0666)
+rescue
+    # add error handling here
+end
+
+
+# @@PLEAC@@_14.3
+# sdbm2gdbm: converts sdbm database to a gdbm database
+require "sdbm"
+require "gdbm"
+
+unless ARGV.length == 2
+    fail "usage: sdbm2gdbm infile outfile"
+end
+infile = ARGV[0]
+outfile = ARGV[1]
+
+sdb = SDBM.open(infile)
+gdb = GDBM.open(outfile, 0666)
+sdb.each { |key, val|
+    gdb[key] = val
+}
+gdb.close
+sdb.close
+
+
+# @@PLEAC@@_14.4
+#!/usr/bin/ruby -w
+# dbmmerge: merges two dbm databases
+require "sdbm"
+
+unless ARGV.length == 3
+    fail "usage: dbmmerge indb1 indb2 outdb"
+end
+infile1 = ARGV[0]
+infile2 = ARGV[0]
+outfile = ARGV[2]
+
+in1 = SDBM.open(infile1, nil)
+in2 = SDBM.open(infile2, nil)
+outdb = SDBM.open(outfile, 0666)
+
+[in1, in2].each { |indb|
+    indb.each { |key, val|
+        if outdb.has_key?(key)
+            # decide which value to set.
+            # set outdb[key] if necessary
+        else
+            outdb[key] = val
+        end
+    }
+}
+in1.close
+in2.close
+outdb.close
+
+
+# @@PLEAC@@_14.7
+# we write a tie method that extends the Array class.
+# It reads the file into the memory, executes the code block
+# in which you can manipulate the array as needed, and writes
+# the array back to the file after the end of the block execution
+class Array
+    def tie(filename, flags)
+        File.open(filename, flags) { |f|
+            f.each_line { |line|
+                self.push(line.chomp)
+            }
+            yield
+            f.rewind
+            each { |line|
+                if line
+                    f.puts(line)
+                else
+                    f.puts ""
+                end
+            }
+        }
+    end
+end
+
+array = Array.new
+array.tie("/tmp/textfile.txt", File::RDWR|File::CREAT) {
+    array[4] = "a new line 4"
+}
+
+# The tied array can be manipulated like a normal array,
+# so there is no need for a special API, and the recno_demo program
+# to demonstrate is API is useless
+
+
+# tied array demo: show how to use array with a tied file
+filename = "db_file.txt"
+lines = Array.new
+File.unlink(filename) if File.exists?(filename)
+lines.tie(filename, File::RDWR | File::CREAT) {
+    # first create a textfile to play with
+    lines[0] = "zero"
+    lines[1] = "one"
+    lines[2] = "two"
+    lines[3] = "three"
+    lines[4] = "four"
+
+    # print the records in order.
+    # Opposed to perl, the tied array behaves exactly as a normal array
+    puts "\nOriginal"
+    for i in 0..(lines.length-1)
+        puts "#{i}: #{lines[i]}"
+    end
+
+    #use push and pop
+    a = lines.pop
+    lines.push("last")
+    puts("The last line was [#{a}]")
+
+    #use shift and unshift
+    a = lines.shift
+    lines.unshift("first")
+    puts("The first line was [#{a}]")
+
+    # add record after record 2
+    i = 2
+    lines.insert(i + 1, "Newbie")
+
+    # add record before record one
+    i = 1
+    lines.insert(i, "New One")
+
+    # delete record 3
+    lines.delete_at(3)
+
+    #now print the records in reverse order
+    puts "\nReverse"
+    (lines.length - 1).downto(0){ |i|
+        puts "#{i}: #{lines[i]}"
+    }
+
+}
+
+
+# @@PLEAC@@_14.8
+# example to store complex data in a database
+# uses marshall from the standard library
+require "sdbm"
+db = SDBM.open("pleac14-8-database", 0666)
+
+# convert the Objects into strings and back by using the Marshal module.
+# Most normal objects can be converted out of the box,
+# but not special things like procedure objects,
+# IO instance variables, singleton objects
+
+db["Tom Christiansen"] = Marshal.dump(["book author",  "tchrist@perl.com"])
+db["Tom Boutell"] = Marshal.dump(["shareware author",
+"boutell@boutell.com"])
+
+name1 = "Tom Christiansen"
+name2 = "Tom Boutell"
+
+tom1 = Marshal.load(db[name1])
+tom2 = Marshal.load(db[name2])
+
+puts "Two Toming: #{tom1} #{tom2}"
+
+if tom1[0] == tom2[0] && tom1[1] == tom2[1]
+   puts "You're having runtime fun with one Tom made two."
+else
+   puts "No two Toms are ever alike"
+end
+
+# To change parts of an entry, get the whole entry, change the parts,
+# and save the whole entry back
+entry = Marshal.load(db["Tom Boutell"])
+entry[0] = "Poet Programmer"
+db["Tom Boutell"] = Marshal.dump(entry)
+db.close
+
+
+# @@PLEAC@@_14.9
+# example to make data persistent
+# uses Marshal from the standard lib
+# Stores the data in a simple file,
+# see 14.8 on how to store it in a dbm file
+
+# The BEGIN block is executed before the rest of the script
+# we use global variables here because local variables
+# will go out of scope and are not accessible from the main script
+
+BEGIN {
+   $persistent_store = "persitence.dat"
+   begin
+     File.open($persistent_store) do |f|
+       $stringvariable1 = Marshal.load(f)
+       $arrayvariable2 = Marshal.load(f)
+     end
+   rescue
+     puts "Can not open #{$persistent_store}"
+     # Initialisation if this script runs the first time
+     $stringvariable1 = ""
+     $arrayvariable2 = []
+   end
+}
+
+END {
+   File.open($persistent_store, "w+") do |f|
+     Marshal.dump($stringvariable1, f)
+     Marshal.dump($arrayvariable2, f)
+   end
+}
+
+# simple test program
+puts $stringvariable1
+puts $arrayvariable2
+$stringvariable1 = "Hello World"
+$arrayvariable2.push(5)
+puts $stringvariable1
+puts $arrayvariable2
+
+
+# @@PLEAC@@_14.10
+#!/usr/bin/ruby -w
+# Ruby has a dbi module with an architecture similar
+# to the Perl dbi module: the dbi module provides an unified
+# interface and uses specialized drivers for each dbms vendor
+#
+begin
+    DBI.connect("DBI:driver:driverspecific", "username", "auth") {
+        |dbh|
+
+        dbh.do(SQL1)
+
+        dbh.prepare(SQL2){ |sth|
+            sth.execute
+            sth.fetch {|row|
+                # ...
+            }
+        } # end of block finishes the statement handle
+    } # end of block closes the database connection
+rescue DBI::DatabaseError => e
+    puts "dbi error occurred"
+    puts "Error code: #{e.err}"
+    puts "Error message: #{e.errstr}"
+end
+
+#!/usr/bin/ruby -w
+# dbusers - example for mysql which creates a table,
+# fills it with values, retrieves the values back,
+# and finally destroys the table.
+
+require "dbi"
+
+# replacement for the User::pwnt module
+def getpwent
+    result = []
+    File.open("/etc/passwd") {|file|
+        file.each_line {|line|
+            next if line.match(/^#/)
+            cols = line.split(":")
+            result.push([cols[2], cols[0]])
+        }
+    }
+    result
+end
+
+begin
+    DBI.connect("DBI:Mysql:pleacdatabase", "pleac", "pleacpassword") {
+        |conn|
+
+        conn.do("CREATE TABLE users (uid INT, login CHAR(8))")
+
+        users = getpwent
+
+        conn.prepare("INSERT INTO users VALUES (?,?)") {|sth|
+            users.each {|entry|
+                sth.execute(entry[0], entry[1])
+            }
+        }
+
+        conn.execute("SELECT uid, login FROM users WHERE uid < 50") {|sth|
+            sth.fetch {|row|
+                puts row.collect {|col|
+                    if col.nil?
+                        "(null)"
+                    else
+                        col
+                    end
+                }.join(", ")
+            }
+        }
+
+        conn.do("DROP TABLE users")
+    }
+rescue DBI::DatabaseError => e
+    puts "dbi error occurred"
+    puts "Error code: #{e.err}"
+    puts "Error message: #{e.errstr}"
+end
+
+
+# @@PLEAC@@_15.1
+# This test program demonstrates parsing program arguments.
+# It uses the optparse library, which is included with ruby 1.8
+# It handles classic unix style and gnu style options
+require 'optparse'
+
+@debugmode = false
+@verbose = false
+
+ARGV.options do |opts|
+    opts.banner = "Usage: ruby #{$0} [OPTIONS] INPUTFILES"
+
+    opts.on("-h", "--help", "show this message") {
+        puts opts
+        exit
+    }
+    # The OptionParser#on method is called with a specification of short
+    # options, of long options, a data type spezification and user help
+    # messages for this option.
+    # The method analyses the given parameter and decides what it is,
+    # so you can leave out the long option if you don't need it
+    opts.on("-v", "--[no-]verbose=[FLAG]", TrueClass, "run verbosly") {
+        |@verbose|   # sets @verbose to true or false
+    }
+    opts.on("-D", "--DEBUG", TrueClass, "turns on debug mode" ){
+        |@debugmode|   # sets @debugmode to true
+    }
+    opts.on("-c", "--count=NUMBER", Integer, "how many times we do it" ){
+        |@count|      # sets @count to given integer
+    }
+    opts.on("-o", "--output=FILE", String, "file to write output to"){
+        |@outputfile|   # sets @outputfile to given string
+    }
+    opts.parse!
+end
+
+# example to use the options in the main program
+puts "Verbose is on" if @verbose
+puts "Debugmode is on" if @debugmode
+puts "Outfile is #{@outputfile}" if defined? @outputfile
+puts "Count is #{@count}" if defined? @count
+ARGV.each { |param|
+    puts "Got parameter #{param}"
+}
+
+
+# @@PLEAC@@_15.4
+buf = "\0" * 8
+$stdout.ioctl(0x5413, buf)
+ws_row, ws_col, ws_xpixel, ws_ypixel = buf.unpack("S4")
+
+raise "You must have at least 20 characters" unless ws_col >= 20
+max = 0
+values = (1..5).collect { rand(20) }  # generate an array[5] of rand values
+for i in values
+    max = i if max < i
+end
+ratio = Float(ws_col-12)/max          # chars per unit
+for i in values
+    printf "%8.1f %s\n", i, "*" * (ratio*i)
+end
+
+# gives, for example:
+#   15.0 *******************************
+#   10.0 *********************
+#    5.0 **********
+#   14.0 *****************************
+#   18.0 **************************************
+
+
+# @@PLEAC@@_16.1
+output = `program args`       # collect output into one multiline string
+output = `program args`.split # collect output into array, one line per
+element
+
+readme = IO.popen("ls")
+output = ""
+while readme.gets do
+    output += $_
+end
+readme.close
+
+`fsck -y /dev/rsd1a`  # BAD AND SCARY in Perl because it's managed by the shell
+                      # I donna in Ruby ...
+
+# so the "clean and secure" version
+readme, writeme = IO.pipe
+pid = fork {
+    # child
+    $stdout = writeme
+    readme.close
+    exec('find', '..')
+}
+# parent
+Process.waitpid(pid, 0)
+writeme.close
+while readme.gets do
+    # do something with $_
+end
+
+
+# @@PLEAC@@_16.2
+status = system("xemacs #{myfile}")
+
+status = system("xemacs", myfile)
+
+system("cmd1 args | cmd2 | cmd3 >outfile")
+system("cmd args <infile >outfile 2>errfile")
+
+# stop if the command fails
+raise "$program exited funny: #{$?}" unless system("cmd", "args1", "args2")
+
+# get the value of the signal sent to the child
+# even if it is a SIGINT or SIGQUIT
+system(arglist)
+raise "program killed by signal #{$?}" if ($? & 127) != 0
+
+pid = fork {
+    trap("SIGINT", "IGNORE")
+    exec("sleep", "10")
+}
+trap ("SIGINT") {
+    puts "Tsk tsk, no process interruptus"
+}
+Process.waitpid(pid, 0)
+
+# Ruby doesn't permit to lie to the program called by a 'system'.
+# (ie specify what return argv[0] in C, $0 in Perl/Ruby ...)
+# A (dirty) way is to create a link (under Unix), run this link and
+# erase it. Somebody has a best idea ?
+
+
+# @@PLEAC@@_16.3
+exec("archive *.data")
+
+exec("archive", "accounting.data")
+
+exec("archive accounting.data")
+
+
+# @@PLEAC@@_16.4
+# read the output of a program
+IO.popen("ls") {|readme|
+    while readme.gets do
+        # ...
+    end
+}
+# or
+readme = IO.popen("ls")
+while readme.gets do
+    # ...
+end
+readme.close
+
+# "write" in a program
+IO.popen("cmd args","w") {|pipe|
+    pipe.puts("data")
+    pipe.puts("foo")
+}
+
+# close wait for the end of the process
+read = IO.popen("sleep 10000") # child goes to sleep
+read.close                     # and the parent goes to lala land
+
+writeme = IO.popen("cmd args", "w")
+writeme.puts "hello" # program will get hello\n on STDIN
+writeme.close        # program will get EOF on STDIN
+
+# send in a pager (eg less) all output
+$stdout = IO.popen("/usr/bin/less","w")
+print "huge string\n" * 10000
+
+
+# @@PLEAC@@_16.5
+#-----------------------------
+def head(lines = 20)
+    pid = open("|-","w")
+    if pid == nil
+        return
+    else
+        while gets() do
+            pid.print
+            lines -= 1
+            break if lines == 0
+        end
+    end
+    exit
+end
+
+head(100)
+while gets() do
+    print
+end
+#-----------------------------
+1: > Welcome to Linux, version 2.0.33 on a i686
+
+2: > 
+
+3: >     "The software required `Windows 95 or better', 
+
+4: >      so I installed Linux."  
+#-----------------------------
+> 1: Welcome to Linux, Kernel version 2.0.33 on a i686
+
+> 2: 
+
+> 3:     "The software required `Windows 95 or better', 
+
+> 4:      so I installed Linux."  
+#-----------------------------
+#!/usr/bin/ruby
+# qnumcat - demo additive output filters
+
+def number()
+    pid = open("|-","w")
+    if pid == nil
+        return
+    else
+        while gets() do pid.printf("%d: %s", $., $_); end
+    end
+    exit
+end
+
+def quote()
+    pid = open("|-","w")
+    if pid == nil
+        return
+    else
+        while gets() do pid.print "> #{$_}" end
+    end
+    exit
+end
+
+number()
+quote()
+
+while gets() do
+    print
+end
+$stdout.close
+exit
+
+
+# @@PLEAC@@_16.6
+ARGV.map! { |arg|
+    arg =~ /\.(gz|Z)$/ ? "|gzip -dc #{arg}" : arg
+}
+for file in ARGV
+    fh = open(file)
+    while fh.gets() do
+        # .......
+    end
+end
+#-----------------------------
+ARGV.map! { |arg|
+    arg =~ %r#^\w+://# ? "|GET #{arg}" : arg   #
+}
+for file in ARGV
+    fh = open(file)
+    while fh.gets() do
+        # .......
+    end
+end
+#-----------------------------
+pwdinfo = (`domainname` =~ /^(\(none\))?$/) ? '/etc/passwd' : '|ypcat  passwd';
+pwd = open(pwdinfo);
+#-----------------------------
+puts "File, please? ";
+file = gets().chomp();
+fh = open(file);
+
+
+# @@PLEAC@@_16.7
+output = `cmd 2>&1`                            # with backticks
+# or
+ph = open("|cmd 2>&1")                         # with an open pipe
+while ph.gets() { }                            # plus a read
+#-----------------------------
+output = `cmd 2>/dev/null`                     # with backticks
+# or
+ph = open("|cmd 2>/dev/null")                  # with an open pipe
+while ph.gets() { }                            # plus a read
+#-----------------------------
+output = `cmd 2>&1 1>/dev/null`                # with backticks
+# or
+ph = open("|cmd 2>&1 1>/dev/null")             # with an open pipe
+while ph.gets() { }                            # plus a read
+#-----------------------------
+output = `cmd 3>&1 1>&2 2>&3 3>&-`             # with backticks
+# or
+ph = open("|cmd 3>&1 1>&2 2>&3 3>&-")          # with an open pipe
+while ph.gets() { }                            # plus a read
+#-----------------------------
+system("program args 1>/tmp/program.stdout 2>/tmp/program.stderr") 
+#-----------------------------
+output = `cmd 3>&1 1>&2 2>&3 3>&-`  
+#-----------------------------
+fd3 = fd1 
+fd1 = fd2 
+fd2 = fd3 
+fd3 = nil 
+#-----------------------------
+system("prog args 1>tmpfile 2>&1") 
+system("prog args 2>&1 1>tmpfile") 
+#-----------------------------
+# system ("prog args 1>tmpfile 2>&1") 
+fd1 = "tmpfile"          # change stdout destination first
+fd2 = fd1                # now point stderr there, too
+#-----------------------------
+# system("prog args 2>&1 1>tmpfile") 
+fd2 = fd1                # stderr same destination as stdout
+fd1 = "tmpfile"          # but change stdout destination 
+#-----------------------------
+# It is often better not to rely on the shell, 
+# because of portability, possible security problems 
+# and bigger resource usage. So, it is often better to use the open3 library. 
+# See below for an example.
+# opening stdin, stdout, stderr
+require "open3"
+stdin, stdout, stderr = Open3.popen('cmd')
+
+
+# @@PLEAC@@_16.8
+#-----------------------------
+# Contrary to perl, we don't need to use a module in Ruby
+fh = Kernel.open("|" + program, "w+")
+fh.puts "here's your input\n"
+output = fh.gets()
+fh.close()
+#-----------------------------
+Kernel.open("|program"),"w+")    # RIGHT !
+#-----------------------------
+# Ruby has already object methods for I/O handles
+#-----------------------------
+begin
+    fh = Kernel.open("|" + program_and_options, "w+")
+rescue
+    if ($@ ~= /^open/)
+        $stderr.puts "open failed : #{$!} \n #{$@} \n"
+        break
+    end
+    raise      # reraise unforseen exception
+end
+
+
+# @@PLEAC@@_16.13
+#% kill -l
+#HUP INT QUIT ILL TRAP ABRT BUS FPE KILL USR1 SEGV USR2 PIPE
+#ALRM TERM CHLD CONT STOP TSTP TTIN TTOU URG XCPU XFSZ VTALRM
+#PROF WINCH POLL PWR
+#-----------------------------
+#% ruby -e 'puts Signal.list.keys.join(" ")'
+#PWR USR1 BUS USR2 TERM SEGV KILL POLL STOP SYS TRAP IOT HUP INT                                                                          #
+#WINCH XCPU TTIN CLD TSTP FPE IO TTOU PROF CHLD CONT PIPE ABRT
+#VTALRM QUIT ILL XFSZ URG ALRM
+#-----------------------------
+# After that, the perl script create an hash equivalent to Signal.list, 
+# and an array. The array can be obtained by :
+signame = []
+Signal.list.each { |name, i| signame[i] = name }
+
+
+# @@PLEAC@@_16.14
+Process.kill(9, pid)                    # send $pid a signal 9
+Process.kill(-1, Process.getpgrp())     # send whole job a signal 1
+Process.kill("USR1", $$)                # send myself a SIGUSR1
+Process.kill("HUP", pid1, pid2, pid3)   # send a SIGHUP to processes in @pids
+#-----------------------------
+begin
+    Process.kill(0, minion)
+    puts "#{minion} is alive!"
+rescue Errno::EPERM                     # changed uid
+    puts "#{minion} has escaped my control!";
+rescue Errno::ESRCH
+    puts "#{minion} is deceased.";      # or zombied
+rescue
+    puts "Odd; I couldn't check the status of #{minion} : #{$!}"
+end
+
+
+# @@PLEAC@@_16.15
+Kernel.trap("QUIT", got_sig_quit)       # got_sig_quit = Proc.new { puts "Quit\n" }
+trap("PIPE", "got_sig_quit")            # def got_sig_pipe ...
+trap("INT") { ouch++ }                  # increment ouch for every SIGINT
+#-----------------------------
+trap("INT", "IGNORE")                   # ignore the signal INT
+#-----------------------------
+trap("STOP", "DEFAULT")                 # restore default STOP signal handling
+
+
+# @@PLEAC@@_16.16
+# the signal handler
+def ding
+    trap("INT", "ding")
+    puts "\aEnter your name!"
+end
+
+# prompt for name, overriding SIGINT
+def get_name
+    save = trap("INT", "ding")
+
+    puts "Kindly Stranger, please enter your name: "
+    name = gets().chomp()
+    trap("INT", save)
+    name
+end
+
+
+# @@PLEAC@@_16.21
+# implemented thanks to http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/1760
+require 'timeout'
+
+# we'll do something vastly more useful than cookbook to demonstrate timeouts
+begin
+    timeout(5) {
+        waitsec = rand(10)
+        puts "Let's see if a sleep of #{waitsec} seconds is longer than 5 seconds..."
+        system("sleep #{waitsec}")
+    }
+    puts "Timeout didn't occur"
+rescue Timeout::Error    
+    puts "Timed out!"
+end
+
+
+# @@PLEAC@@_17.1
+# A basic TCP client connection
+require 'socket'
+begin
+    t = TCPSocket.new('www.ruby-lang.org', 'www')
+rescue
+    puts "error: #{$!}"
+else
+    # ... do something with the socket
+    t.print "GET / HTTP/1.0\n\n"
+    answer = t.gets(nil)
+    # and terminate the connection when we're done
+    t.close
+end
+
+# Using the evil low level socket API
+require 'socket'
+# create a socket
+s = Socket.new(Socket::AF_INET, Socket::SOCK_STREAM, 0)
+# build the address of the remote machine
+sockaddr_server = [Socket::AF_INET, 80,
+    Socket.gethostbyname('www.ruby-lang.org')[3],
+    0, 0].pack("snA4NN")
+# connect
+begin
+    s.connect(sockaddr_server)
+rescue
+    puts "error: #{$!}"
+else
+    # ... do something with the socket
+    s.print "GET / HTTP/1.0\n\n"
+    # and terminate the connection when we're done
+    s.close
+end
+
+# TCP connection with management of error (DNS)
+require 'socket'
+begin
+    client = TCPSocket.new('does not exists', 'www')
+rescue
+    puts "error: #{$!}"
+end
+
+# TCP connection with a time out
+require 'socket'
+require 'timeout'
+begin
+    timeout(1) do #the server has one second to answer
+        client = TCPSocket.new('www.host.com', 'www')
+    end
+rescue
+    puts "error: #{$!}"
+end
+
+
+# @@PLEAC@@_17.12
+require 'socket'
+
+class Preforker 
+    attr_reader (:child_count)
+    
+    def initialize(prefork, max_clients_per_child, port, client_handler)
+        @prefork = prefork
+        @max_clients_per_child = max_clients_per_child
+        @port = port
+        @child_count = 0
+        
+        @reaper = proc {
+            trap('CHLD', @reaper)
+            pid = Process.wait
+            @child_count -= 1
+        }
+        
+        @huntsman = proc {
+            trap('CHLD', 'IGNORE')
+            trap('INT', 'IGNORE')
+            Process.kill('INT', 0)
+            exit
+        }
+        
+        @client_handler=client_handler
+    end
+    
+    def child_handler
+        trap('INT', 'EXIT')
+        @client_handler.setUp
+        # wish: sigprocmask UNblock SIGINT
+        @max_clients_per_child.times {
+            client = @server.accept or break
+            @client_handler.handle_request(client)
+            client.close
+        }
+        @client_handler.tearDown
+    end
+    
+    def make_new_child
+        # wish: sigprocmask block SIGINT
+        @child_count += 1
+        pid = fork do
+            child_handler
+        end
+        # wish: sigprocmask UNblock SIGINT
+    end
+    
+    def run
+        @server = TCPserver.open(@port)
+        trap('CHLD', @reaper)
+        trap('INT', @huntsman)
+        loop {
+            (@prefork - @child_count).times { |i|
+                make_new_child
+            }
+            sleep .1
+        }
+    end
+end
+
+#-----------------------------
+#!/usr/bin/ruby
+
+require 'Preforker'
+
+class ClientHandler
+    def setUp
+    end
+    
+    def tearDown
+    end
+    
+    def handle_request(client)
+        # do stuff
+    end
+end
+
+server = Preforker.new(1, 100, 3102, ClientHandler.new)
+server.run
+
+
+# @@PLEAC@@_18.2
+require 'net/ftp'
+
+begin
+    ftp = Net::FTP::new("ftp.host.com")
+    ftp.login(username,password)
+    ftp.chdir(directory)
+    ftp.get(filename)
+    ftp.put(filename)
+rescue Net::FTPError
+    $stderr.print "FTP failed: " + $!
+ensure
+    ftp.close() if ftp
+end
+
+# A better solution for a local use could be :
+Net::FTP::new("ftp.host.com") do |ftp|
+    ftp.login(username,password)
+    ftp.chdir(directory)
+    ftp.get(filename)
+    ftp.put(filename)
+end
+
+# If you have only one file to get, there is a simple solution :
+require 'open-uri'
+open("ftp://www.ruby-lang.org/path/filename") do |fh|
+    # read from filehandle fh
+end 
+#--------------------------------------------
+# to wait a defined time for the connection, 
+# use the timeout module
+require 'timeout'
+begin 
+    timeout(30){
+        ftp = Net::FTP::new("ftp.host.com")
+        ftp.debug_mode = true
+    }
+rescue Net::FTPError
+    $stderr.puts "Couldn't connect."
+rescue Timeout::Error
+    $stderr.puts "Timeout while connecting to server."
+end
+
+begin
+    ftp.login()
+rescue Net::FTPError
+    $stderr.print "Couldn't authentificate.\n"
+end
+
+begin
+    ftp.login(username)
+rescue Net::FTPError
+    $stderr.print "Still couldn't authenticate.\n"
+end
+
+begin
+    ftp.login(username, password)
+rescue Net::FTPError
+    $stderr.print "Couldn't authenticate, even with explicit
+    username and password.\n"
+end
+
+begin
+    ftp.login(username, password, account)
+rescue Net::FTPError
+    $stderr.print "No dice. It hates me.\n"
+end
+#-----------------------------
+ftp.put(localfile, remotefile)
+#-----------------------------
+# Sending data from STDIN is not directly supported 
+# by the ftp library module. A possible way to do it is to use the 
+# storlines method directly to send raw commands to the ftp server.
+#-----------------------------
+ftp.get(remotefile, localfile)
+#-----------------------------
+ftp.get(remotefile) { |data| puts data }
+#-----------------------------
+ftp.chdir("/pub/ruby") 
+print "I'm in the directory ", ftp.pwd(), "\n"
+#-----------------------------
+ftp.mkdir("/pub/ruby/new_dir")
+#-----------------------------
+lines = ftp.ls("/pub/ruby/")
+# => ["drwxr-xr-x 2 matz users 4096 July 17 1998 1.0", ... ]
+
+latest = ftp.dir("/pub/ruby/*.tgz").sort.last
+
+ftp.nlst("/pub/ruby")
+# => ["/pub/ruby/1.0", ... ]
+#-----------------------------
+ftp.quit()
+
+
+# @@PLEAC@@_18.6
+require 'net/telnet'
+t = Net::Telnet::new( "Timeout" => 10,
+                      "Prompt"  => /%/,
+                      "Host"    => host )
+t.login(username, password)
+files = t.cmd("ls")
+t.print("top")
+process_string = t.waitfor(/\d+ processes/)
+t.close
+#-----------------------------
+/[$%#>] \z/n
+#-----------------------------
+# In case of an error, the telnet module throws an exception.
+# For control of the behavior in case of an error,
+# you just need to catch the exceptions and do your custom
+# error handling.
+#-----------------------------
+begin
+    telnet.login(username, password)
+rescue TimeoutError
+    fail "Login failed !\n"
+end
+#-----------------------------
+telnet.waitfor('/--more--/')
+#-----------------------------
+telnet.waitfor(String => 'greasy smoke', Timeout => 30)
+
+
+# @@PLEAC@@_18.7
+require 'ping'
+
+puts "#{host} is alive.\n" if Ping.pingecho(host);
+#-----------------------------
+# the ping module only use TCP ping, not ICMP even if we are root
+if Ping.pingecho("kingkong.com")
+    puts "The giant ape lives!\n";
+else
+    puts "All hail mighty Gamera, friend of children!\n";
+end
+
+
+# @@PLEAC@@_19.0
+#-----------------------------
+# http://www.perl.com/CPAN/
+# http://www.perl.com:8001/bad/mojo.html
+# ftp://gatekeeper.dec.com/pub/misc/netlib.tar.Z
+# ftp://anonymous@myplace:gatekeeper.dec.com/pub/misc/netlib.tar.Z
+# file:///etc/motd
+#-----------------------------
+# http://mox.perl.com/cgi-bin/program?name=Johann&born=1685
+#-----------------------------
+# http://mox.perl.com/cgi-bin/program
+#-----------------------------
+
+
+# @@PLEAC@@_19.1
+#!/usr/local/bin/ruby -w
+# hiweb - load CGI class to decode information given by web server
+
+require 'cgi'
+
+cgi = CGI.new('html3')
+
+# get a parameter from a form
+value = cgi.params['PARAM_NAME'][0]
+
+# output a document
+cgi.out {
+    cgi.html {
+        cgi.head { cgi.title { "Howdy there!" } } +
+            cgi.body { cgi.p { "You typed: " + cgi.tt {
+                    CGI.escapeHTML(value) } } }
+    }
+}
+
+require 'cgi'
+cgi = CGI.new
+who   = cgi.param["Name"][0]     # first param in list
+phone = cgi.param["Number"][0]
+picks = cgi.param["Choices"]     # complete list
+
+print cgi.header( 'type' => 'text/plain',
+                  'expires' => Time.now + (3 * 24 * 60 * 60) )
+
+
+# @@PLEAC@@_19.3
+#!/usr/local/bin/ruby -w
+# webwhoami - show web user's id
+require 'etc'
+print "Content-Type: text/plain\n\n"
+print "Running as " + Etc.getpwuid.name + "\n"
+
+# % ruby -wc cgi-script     # just check syntax
+
+# % ruby -w  cgi-script     # params from stdin
+# (offline mode: enter name=value pairs on standard input)
+# name=joe
+# number=10
+# ^D
+
+# % ruby -w  cgi-script name=joe number=10     # run with mock form input
+# % ruby -d  cgi-script name=joe number=10     # ditto, under the debugger
+
+# POST method script in csh
+# % (setenv HTTP_METHOD POST; ruby -w cgi-script name=joe number=10)
+# POST method script in sh
+# % HTTP_METHOD=POST perl -w cgi-script name=joe number=10
+
+
+# @@PLEAC@@_19.4
+# ruby has several security levels, the level "1" is similar to perls taint mode.
+# It can be switched on by providing the -T command line parameter
+# or by setting $SAFE to 1. Setting $SAFE to 2,3 or 4 restricts possible
+# harmful operations further.
+
+#!/usr/bin/ruby -T
+$SAFE = 1
+File.open(ARGV[0], "w")
+# ruby warns with:
+# taint1.rb:2:in `initialize': Insecure operation - initialize (SecurityError)
+
+$SAFE = 1
+file = ARGV[0]
+unless /^([\w.-]+)$/.match(file)
+    raise "filename #{file} has invalid characters"
+end
+file = $1
+# In ruby, even the back reference from a regular expression stays tainted.
+# you need to explicitly untaint the variable:
+file.untaint
+File.open(file, "w")
+
+# Race condition exists like in perl:
+unless File.exists(filename)        # Wrong because of race condition
+    File.open(filename, "w")
+end
+
+
+# @@PLEAC@@_19.8
+url = "http://pleac.sourceforge.net/pleac_ruby/"
+print "Location: #{url}\r\n\r\n"
+exit
+
+#!/usr/bin/ruby
+require 'cgi'
+
+cgi = CGI.new
+oreo = CGI::Cookie.new('name' => 'filling',
+                       'value' => 'vanilla creme',
+                       'expires' => Time.now + (3 * 30 * 24 * 60 * 60),
+                       'domain' => '.pleac.sourceforge.net')
+
+whither = 'http://pleac.sourceforge.net/pleac_ruby/cgiprogramming.html'
+
+cgi.out('cookie' => oreo,
+        'Location' => whither){""}
+
+#!/usr/bin/ruby
+# os_snipe - redirect to a Jargon File entry about current OS
+dir = 'http://www.elsewhere.org/jargon/html/entry'
+
+agent = ENV['HTTP_USER_AGENT']
+
+page = case
+    when agent =~ /Mac/: 'Macintrash.html'
+    when agent =~ /Win(dows )?NT/: 'evil_and_rude.html'
+    when agent =~ /Win|MSIE|WebTV/: 'Microsloth_Windows.html'
+    when agent =~ /Linux/: 'Linux.html'
+    when agent =~ /HP-UX/: 'HP-SUX.html'
+    when agent =~ /SunOS/: 'ScumOS.html'
+    else 'Appendix_B.html'
+end
+
+print "Location: #{dir}/#{page}\n\n"
+
+require 'cgi'
+cgi = CGI.new
+cgi.out('status' => '204 No response'){""}
+# this produces:
+# Status: 204 No response
+# Content-Type: text/html
+# Content-Length: 0
+# <blank line here>
+
+
+# @@PLEAC@@_19.10
+preference_value = cgi.cookies["preference name"][0]
+
+packed_cookie = CGI::Cookie.new("name" => "preference name",
+                                "value" => "whatever you'd like",
+                                "expires" => Time.local(Time.now.year + 2,
+    Time.now.mon, Time.now.day, Time.now.hour, Time.now.min, Time.now.sec) )
+
+cgi.header("cookie" => [packed_cookie])
+
+#!/usr/local/bin/ruby -w
+# ic_cookies - sample CGI script that uses a cookie
+require 'cgi'
+
+cgi = CGI.new('html3')
+
+cookname = "favorite ice cream"
+favorite = cgi.params["flavor"][0]
+tasty    = cgi.cookies[cookname][0] || 'mint'
+
+unless favorite
+    cgi.out {
+        cgi.html {
+            cgi.head { cgi.title { "Ice Cookies" } } +
+            cgi.body {
+                cgi.h1 { "Hello Ice Cream" } +
+                cgi.hr +
+                cgi.form {
+                    cgi.p { "Please select a flavor: " +
+                            cgi.text_field("flavor", tasty ) }
+                } +
+                cgi.hr
+            }
+        }
+    }
+else
+    cookie = CGI::Cookie.new( "name"    => cookname,
+                              "value"   => favorite,
+                              "expires" => Time.local(Time.now.year + 2,
+Time.now.mon, Time.now.day, Time.now.hour, Time.now.min, Time.now.sec) )
+    cgi.out("cookie" => [cookie]) {
+        cgi.html {
+            cgi.head { cgi.title { "Ice Cookies" } } +
+            cgi.body {
+                cgi.h1 { "Hello Ice Cream" } +
+                cgi.p { "You chose as your favorite flavor `#{favorite}'." }
+            }
+        }
+    }
+end
+
+
+# @@PLEAC@@_20.9
+def templatefile(filename, fillings)
+    aFile = File.new(filename, "r")
+    text = aFile.read()
+    aFile.close()
+    pattern = Regexp.new('%%(.*?)%%')
+    text.gsub!(pattern) {
+        fillings[$1] || ""
+    }
+    text
+end
+
+fields = {
+    'username' => whats_his_name,
+    'count' => login_count,
+    'total' => minutes_used
+}
+puts templatefile('simple.template', fields)
+
+# @@INCOMPLETE@@
+# An example using databases is missing
+
+