Python example that shows how to run non-interactive shell commands using two different subprocess implementations.

runcmd.py

#!/usr/bin/env python
'''
Python example that shows how to run non-interactive shell commands using
two different subprocess implementations.

Works in Python 2.7 and Python 3.x.

LICENSE (MIT Open Source)

Copyright (c) 2016 Joe Linoff

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
'''
import subprocess
import sys

def __runcmd_long(cmd, show_output=True):
    '''
    Execute a long running shell command with no inputs.

    Capture output and exit status.

    For long running commands, this implementation displays output
    information as it is captured.

    For fast running commands it would be better to use
    subprocess.check_output.
    '''
    proc = subprocess.Popen(cmd,
                            shell=True,
                            stdout=subprocess.PIPE,
                            stderr=subprocess.STDOUT)

    # Read the output 1 character at a time so that it can be
    # displayed in real time.
    output = ''
    while not proc.returncode:
        char = proc.stdout.read(1)
        if not char:
            # all done, wait for returncode to get populated
            break
        else:
            ascii_char = char.decode('ascii')  # byte --> char in Python 3
            output += ascii_char
            if show_output:
                sys.stdout.write(ascii_char)
                sys.stdout.flush()
    proc.wait()
    return proc.returncode, output


def __runcmd_short(cmd, show_output=True):
    '''
    Execute a short running shell command with no inputs.

    Capture output and exit status.
    '''
    try:
        output = subprocess.check_output(cmd, stderr=subprocess.STDOUT, shell=True)
        status = 0
    except subprocess.CalledProcessError as obj:
        output = obj.output.decode('ascii')
        status = obj.returncode

    output = output.decode('ascii')  # byte --> char in Python 3
    if show_output:
        sys.stdout.write(output)

    return status, output


def __runcmd_interactive(cmd):
    '''
    Run an interactive command.
    
    Return the status.
    '''
    try:
        args = shlex.split(cmd)
        status = subprocess.call(cmd, shell=True)
    except subprocess.CalledProcessError as obj:
        status = obj.returncode
    return status


def test():
    '''
    Treat each command line argument as a separate command.

    The --long argument specifies the use of __runcmd_long.
    It is modal so all subsequent commands use __runcmd_long until
    --short is specified.

    The --short argument specifies the use of __runcmd_short.
    It is modal so all subsequent commands use __runcmd_short until
    --long is specified.

    The default is --short.

    Here are some examples to show how it is used:

    $ runcmd.py 'ls -l' 'hostname -f'
    $ runcmd.py --long 'ls -l' 'hostname -f'
    $ runcmd.py --long 'ls -l' --short 'hostname -f'
    '''
    runcmd = __runcmd_short
    for i in range(1, len(sys.argv)):
        arg = sys.argv[i]
        if arg == '--short':
            runcmd = __runcmd_short
        elif arg == '--long':
            runcmd = __runcmd_long
        else:
            print('Function: {}'.format(runcmd.__name__))
            print('Command: {}'.format(arg))
            status, _ = runcmd(arg)
            print('Status: {}'.format(status))


if __name__ == '__main__':
    test()