Updated ProcReader to determine which of the process streams are pipes

2 files changed, 23 insertions, 10 deletions

diff --git a/cmd2/cmd2.py b/cmd2/cmd2.py
index 6f0835e0..c33e2927 100644
--- a/cmd2/cmd2.py
+++ b/cmd2/cmd2.py
@@ -2941,13 +2941,18 @@ class Cmd(cmd.Cmd):
 
         expanded_command = ' '.join(tokens)
 
-        # If stdout is a StdSim, then we will use pipes so we can save stdout and stderr output
-        if isinstance(self.stdout, utils.StdSim):
-            proc = subprocess.Popen(expanded_command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
+        # For any output that is a StdSim, we will use a pipe so we can save the output
+        is_out_sim = isinstance(self.stdout, utils.StdSim)
+        is_err_sim = isinstance(sys.stderr, utils.StdSim)
+
+        proc_stdout = subprocess.PIPE if is_out_sim else self.stdout
+        proc_stderr = subprocess.PIPE if is_err_sim else sys.stderr
+
+        proc = subprocess.Popen(expanded_command, stdout=proc_stdout, stderr=proc_stderr, shell=True)
+        if is_out_sim or is_err_sim:
             proc_reader = utils.ProcReader(proc, self.stdout, sys.stderr)
             proc_reader.wait()
         else:
-            proc = subprocess.Popen(expanded_command, stdout=self.stdout, shell=True)
             proc.communicate()
 
     @staticmethod
diff --git a/cmd2/utils.py b/cmd2/utils.py
index a0026eba..45c7ca6a 100644
--- a/cmd2/utils.py
+++ b/cmd2/utils.py
@@ -371,7 +371,7 @@ class ByteBuf(object):
 
 
 class ProcReader(object):
-    """Used to read stdout and stderr from a Popen process whose stdout and stderr are set to binary pipes"""
+    """Used to read stdout and stderr from a Popen process if any of those were set to subprocess.PIPE"""
     def __init__(self, proc: subprocess.Popen, stdout: Union[StdSim, BinaryIO, TextIO],
                  stderr: Union[StdSim, BinaryIO, TextIO]) -> None:
         """
@@ -390,9 +390,11 @@ class ProcReader(object):
         self._err_thread = threading.Thread(name='out_thread', target=self._reader_thread_func,
                                             kwargs={'read_stdout': False})
 
-        # Start reading from the process
-        self._out_thread.start()
-        self._err_thread.start()
+        # Start the reader threads for pipes only
+        if self._proc.stdout is not None:
+            self._out_thread.start()
+        if self._proc.stderr is not None:
+            self._err_thread.start()
 
     def terminate(self) -> None:
         """Terminates the process being run"""
@@ -400,10 +402,13 @@ class ProcReader(object):
 
     def wait(self) -> None:
         """Wait for the process to finish"""
-        self._out_thread.join()
-        self._err_thread.join()
+        if self._out_thread.is_alive():
+            self._out_thread.join()
+        if self._err_thread.is_alive():
+            self._err_thread.join()
 
         # Handle case where the process ended before the last read could be done
+        # This will return None for the streams that weren't pipes so it is safe.
         out, err = self._proc.communicate()
         if out:
             self._write_bytes(self._stdout, out)
@@ -422,6 +427,9 @@ class ProcReader(object):
             read_stream = self._proc.stderr
             write_stream = self._stderr
 
+        # The thread should have been started only if this stream was a pipe
+        assert read_stream is not None
+
         # Run until process completes
         while self._proc.poll() is None:
             # noinspection PyUnresolvedReferences