python: string as stdin to subcommand

Question

I have a python script in which I need to invoke a shell command. The shell command can accept its input from either a file or stdin.

In my script, the input is stored in a variable. What is the proper way to invoke the command? If it matters, the shell command produces no output.

I know I could write the variable's content into a file and invoke the command with the file as argument but that seems inelegant. Surely, there's a better way.

Can someone tell me what it is? Thanks.

I think this answer will be helpful for you http://stackoverflow.com/a/8475367/1374493 — palvarez89, Feb 08 '16 at 01:13
Possible duplicate of [Wrapping an interactive command line application in a python script](http://stackoverflow.com/questions/1567371/wrapping-an-interactive-command-line-application-in-a-python-script) — ivan_pozdeev, Feb 08 '16 at 01:19
Possible duplicate of [how do i write to a python subprocess' stdin](http://stackoverflow.com/questions/8475290/how-do-i-write-to-a-python-subprocess-stdin) — palvarez89, Feb 08 '16 at 01:22

zondo · Accepted Answer · 2016-02-08T01:17:06.523

4

You can use the subprocess module.

import subprocess
process = subprocess.Popen(["Mycommand", "with", "arguments"], stdin=subprocess.PIPE)
process.communicate("My text")

edited Feb 08 '16 at 01:17

answered Feb 08 '16 at 01:11

zondo

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"Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS pipe buffers filling up and blocking the child process." (From https://docs.python.org/2/library/subprocess.html) – palvarez89 Feb 08 '16 at 01:13
@palvarez89 Good call. I fixed it. – zondo Feb 08 '16 at 01:17
`communicate()` is a one-off method. To do that repeatedly, I copied some code from its implementation that handled `stdin` in a separate thread. – ivan_pozdeev Feb 08 '16 at 01:20
@ivan_pozdeev My answer *did* use `process.stdin.write`, but as palvarez89 mentioned, that is not the preferred way. The OP mentioned trying to `write the variable's content into a file and invoke the command with the file as argument`. If it were a problem to use a one-off method, that would not have been suggested. – zondo Feb 08 '16 at 01:23

score 0 · Answer 2 · answered Nov 23 '20 at 21:03

Refer to How do I pass a string into subprocess.Popen (using the stdin argument)?

For python 3.5+ (3.6+ for encoding), you can use input:

from subprocess import check_output   
output = check_output(["cat","-b"],
        input="-foo\n-bar\n-foobar", encoding='ascii')
print(output)

python: string as stdin to subcommand

2 Answers2