Python Programming/External commands

The traditional way of executing external commands is using os.system():

importosos.system("dir")os.system("echo Hello")exitCode=os.system("echotypo")

The modern way, since Python 2.4, is using subprocess module:

subprocess.call(["echo","Hello"])exitCode=subprocess.call(["dir","nonexistent"])

The traditional way of executing external commands and reading their output is via popen2 module:

importpopen2readStream,writeStream,errorStream=popen2.popen3("dir")# allLines = readStream.readlines()forlineinreadStream:print(line.rstrip())readStream.close()writeStream.close()errorStream.close()

The modern way, since Python 2.4, is using subprocess module:

importsubprocessprocess=subprocess.Popen(["echo","Hello"],stdout=subprocess.PIPE)forlineinprocess.stdout:print(line.rstrip())

Keywords: system commands, shell commands, processes, backtick, pipe.

External links

• 17.1. subprocess — Subprocess management, python.org, since Python 2.4
• 15.1. os — Miscellaneous operating system interfaces, python.org
• 17.5. popen2 — Subprocesses with accessible I/O streams, python.org, deprecated since Python 2.6