Run Unix Commands and Other Programs within Python

The python subprocess module is a part of the standard python library that enables a user to run a variety of subprocess within python and collect their output and error pipes. It is a wonderfully handy tool that really expands the possibilities of what python is capable of doing.  The tool is intended to build upon and essentially replace a lot of the functionality of the os package which I have found cumbersome to use.  The main commands of the subprocess module include:

subprocess.call-runs a command and returns output and the exit code
subprocess.check_call-runs a command; if exit code is 0 returns output, otherwise CalledProcessError

Here are some simple example scripts to help get started using the subprocess inside python code:

	import subprocess
	# Call separated by quotes, first quote command others are interpreted as options
	subprocess.call(["echo","Hello world!"])
	# No quotes needed with shell=True option
	subprocess.call("ls -l | grep Music", shell=True)
	# Exit code can be saved as a variable otherwise check_call produces error if non-zero
	exit_code=subprocess.check_call("ls -l | grep .txt", shell=True)
	# Run another program
	subprocess.call("Rscript -e 2+2", shell=True)
	# Output can be saved as a variable
	output=subprocess.Popen("Rscript -e 2+2", shell=True, stdout=subprocess.PIPE).stdout.read()

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