Run Shell Commands in Python

subprocess.call

This is the recommended way to run shell commands in Python compared with old-fashioned os module. This is a "real-time" method, which means you can get the shell output on the fly, compared with following "subprocess.check_output" method, which collect all output in its return value. This method return the return value of the command, for example:

ret = subprocess.call('ls -l')

where ret=0, while

ret = subprocess.call('cd aaa')

ret=2 when there isn't "aaa" subfolder under CWD.

For ease of use, write a shorthand function:

import subprocess
def run(cmd):
    ret = subprocess.call(cmd, shell=True)
    if ret != 0:
        sys.exit('Exec cmd %s error, return value: %s' %(cmd, str(ret)))

Then you can simply use "run(cmd)" as a shell interface. "run" print command stdout stderr to console stdout, and if there's something wrong during execution, we interrupt it.

subprocess.check_output

A more safe way to run shell command is using "check_output" function. If the return value if not 0, a exception raised, otherwise return the command output.

$ cat myrun.py
import subprocess
def run(cmd):
    return subprocess.check_output(cmd, shell=True)
$ python -i myrun.py
>>> ret = run('ls -l|grep donno')
>>> ret
'drwxr-xr-x 6 chad chad 4096 Jan 26 18:18 donno-0.1.10
-rw-r--r-- 1 chad chad 8716 Jan 27 15:53 donno-0.1.10.tar.gz
'
>>> ret = run('cd aaa')
/bin/sh: 1: cd: can't cd to aaa
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "shtest.py", line 3, in run
    return subprocess.check_output(cmd, shell=True)
  File "/usr/lib/python2.7/subprocess.py", line 544, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command 'cd aaa' returned non-zero exit status 2

os.system

If it's unnecessary to save command output, this is most convenient way. The output will output to console. You can use space and pipe in command:

>>> import os 
>>> ret = os.system('ls -l|grep D')

And it will return after the command complete:

>>> ret = os.system('vmstat 3 3')

os.popen

Use this form if you want to save command output.

>>> retfile = os.popen('pwd')
>>> ret = retfile.read() 
>>> ret 
'/home/lichao
' 
>>> retfile 
<open file 'pwd', mode 'r' at 0xb74aad30>

or write it more compact:

>>> result = os.popen('ls|grep enex').read()

subprocess.Popen

If you want some more powerful tools, use this. You can't use pipe directly in this form. Instead, You have to use subprocess.PIPE:

>>> import subprocess
>>> lsres = subprocess.Popen(['ls','-l'], stdout=subprocess.PIPE)
>>> grepres = subprocess.Popen(['grep', 'Do'], stdin=lsres.stdout, stdout=subprocess.PIPE)
>>> res = grepres.communicate()

communicate() interact with process: Send data to stdin. Read data from stdout and stderr, until end-of-file is reached. Wait for process to terminate. It returns a tuple (stdoutdata, stderrdata).

Deprecated

• commands.getoutput()

• commands.getstatusoutput()