Executing shell command in python with file as stdin

Question

In my Python code, I have

executable_filepath = '/home/user/executable'
input_filepath = '/home/user/file.in'

I want to analyze the output I would get in shell from command

/home/user/executable </home/user/file.in

I tried

command = executable_filepath + ' <' + input_filepath
p = subprocess.Popen([command], stdout=subprocess.PIPE)
p.wait()
output = p.stdout.read()

but it doesn't work. The only solution that I can think of now is creating another pipe, and copying input file through it, but there must be a simple way.

chepner · Accepted Answer · 2013-05-21 15:04:47Z

6

from subprocess import check_output

with open("/home/user/file.in", "rb") as file:
    output = check_output(["/home/user/executable"], stdin=file)

edited May 21, 2013 at 15:04

chepner

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answered May 21, 2013 at 14:54

jfs

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Comments

chepner · Accepted Answer · 2013-05-21 14:38:53Z

0

You need to specify shell=True in the call to Popen. By default, [command] is passed directly to a system call in the exec family, which doesn't understand shell redirection operators.

Alternatively, you can let Popen connect the process to the file:

with open(input_filepath, 'r') as input_fh:
    p = subprocess.Popen( [executable_filepath], stdout=subprocess.PIPE, stdin=input_fh)
    p.wait()
    output=p.stdout.read()

answered May 21, 2013 at 14:38

chepner

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1 Comment

jfs Over a year ago

calling .wait() before .stdout.read() can lead to a deadlock if the subprocess generates enough output.

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