Redirect input with subprocess python

Question

How can I use input redirection <() with python's subprocess.Popen?

For example, say I have:

import subprocess


class Test():
    def __init__(self):
        self.proc = subprocess.Popen(["sort file1.txt file2.txt)"],
                                     shell=True,
                                     stdout=subprocess.PIPE,
                                     stderr=subprocess.PIPE)

    def __iter__(self):
        return self

    def __next__(self):
        while True:
            line = self.proc.stdout.readline()
            if not line:
                raise StopIteration
            return line.strip().decode('utf-8')


t = Test()
for line in t:
    print(line)

The above works perfectly fine, but really I need the command to do something like:

sort <(python file1.txt) <(python file2.txt)

That doesnt seem to run anything though, even this doesnt work

sort <(cat file1.txt) <(cat file2.txt)

How can I get this to work with python's subprocess, and iterate through the results line by line

Michael Veksler · Accepted Answer · 2021-12-09 21:03:27Z

2

You should tell subprocess.Popen() to use /bin/bash, which supports the <(..) syntax, instead of the default /bin/sh, which doesn't:

    def __init__(self):
        self.proc = subprocess.Popen(["sort <(cat file1.txt) <(cat file2.txt)"],
                                     shell=True,
                                     executable="/bin/bash",
                                     stdout=subprocess.PIPE,
                                     stderr=subprocess.PIPE)

    def __iter__(self):
        return self

    def __next__(self):
        while True:
            line = self.proc.stdout.readline()
            if not line:
                raise StopIteration
            return line.strip().decode('utf-8')


t = Test()
for line in t:
    print(line)

answered Dec 9, 2021 at 21:03

Michael Veksler

8,5001 gold badge24 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user1179317 Over a year ago

Great, that works perfectly

Collectives™ on Stack Overflow

Redirect input with subprocess python

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related