passing data to subprocess.check_output

Question

I want to invoke a script, piping the contents of a string to its stdin and retrieving its stdout.

I don\'t want to touch the real filesystem so I can\'t create real

Answer 1

Use Popen.communicate instead of subprocess.check_output.

from subprocess import Popen, PIPE

p = Popen([script_name, "-"], stdin=PIPE, stdout=PIPE, stderr=PIPE)
stdout, stderr = p.communicate("this is some input")

Answer 2

In Python 3.4 and newer, you can use the input keyword parameter to send input via STDIN when using subprocess.check_output()

Quoting from the standard library documentation for subprocess.check_output():

The input argument is passed to Popen.communicate() and thus to the subprocess’s stdin. If used it must be a byte sequence, or a string if universal_newlines=True. When used, the internal Popen object is automatically created with stdin=PIPE, and the stdin argument may not be used as well.

Example:

>>> subprocess.check_output(["sed", "-e", "s/foo/bar/"],
...                         input=b"when in the course of fooman events\n")
b'when in the course of barman events\n'
>>> 
>>> # To send and receive strings instead of bytes,
>>> # pass in universal_newlines=True
>>> subprocess.check_output(["sed", "-e", "s/foo/bar/"],
...                         universal_newlines=True,
...                         input="when in the course of fooman events\n")
'when in the course of barman events\n'

Answer 3

Here's a check_output backported version for python 2.7 with input.

from subprocess import (PIPE, Popen, CalledProcessError)

def check_output_input(*popenargs, **kwargs):
    """Run command with arguments and return its output as a byte string.

    If the exit code was non-zero it raises a CalledProcessError.  The
    CalledProcessError object will have the return code in the returncode
    attribute and output in the output attribute.

    The arguments are the same as for the Popen constructor.  Example:

    >>> check_output(["ls", "-l", "/dev/null"])
    'crw-rw-rw- 1 root root 1, 3 Oct 18  2007 /dev/null\n'

    The stdout argument is not allowed as it is used internally.
    To capture standard error in the result, use stderr=STDOUT.

    >>> check_output(["/bin/sh", "-c",
    ...               "ls -l non_existent_file ; exit 0"],
    ...              stderr=STDOUT)
    'ls: non_existent_file: No such file or directory\n'

    There is an additional optional argument, "input", allowing you to
    pass a string to the subprocess's stdin.  If you use this argument
    you may not also use the Popen constructor's "stdin" argument, as
    it too will be used internally.  Example:

    >>> check_output(["sed", "-e", "s/foo/bar/"],
    ...              input=b"when in the course of fooman events\n")
    b'when in the course of barman events\n'

    If universal_newlines=True is passed, the return value will be a
    string rather than bytes.

    """
    if 'stdout' in kwargs:
        raise ValueError('stdout argument not allowed, it will be overridden.')
    if 'input' in kwargs:
        if 'stdin' in kwargs:
            raise ValueError('stdin and input arguments may not both be used.')
        inputdata = kwargs['input']
        del kwargs['input']
        kwargs['stdin'] = PIPE
    else:
        inputdata = None
    process = Popen(*popenargs, stdout=PIPE, **kwargs)
    try:
        output, unused_err = process.communicate(inputdata)
    except:
        process.kill()
        process.wait()
        raise
    retcode = process.poll()
    if retcode:
        cmd = kwargs.get("args")
        if cmd is None:
            cmd = popenargs[0]
        raise CalledProcessError(retcode, cmd, output=output)
    return output