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 temporary files for it.

using subprocess.check_output I can get whatever the script writes; how can I get the input string into its stdin though?

subprocess.check_output([script_name,"-"],stdin="this is some input") Traceback (most recent call last):   File "<stdin>", line 1, in <module>   File "/usr/lib/python2.7/subprocess.py", line 537, in check_output     process = Popen(stdout=PIPE, *popenargs, **kwargs)   File "/usr/lib/python2.7/subprocess.py", line 672, in __init__     errread, errwrite) = self._get_handles(stdin, stdout, stderr)   File "/usr/lib/python2.7/subprocess.py", line 1043, in _get_handles     p2cread = stdin.fileno() AttributeError: 'str' object has no attribute 'fileno' 

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'