Question

Here is my code.

import subprocess

bashCommand = "./program -s file_to_read.txt | ./awk_program.txt"
process = subprocess.Popen(bashCommand.split(), stdout=subprocess.PIPE)
output = process.communicate()[0]
output2 = process.stdout
print output
print output2

This bash command alone when used in terminal prints the output of the awk_program (which just prints to stdout). But in python, output prints nothing and output2 prints

<closed file '<fdopen>', mode 'rb' at 0x2b5b20>

What do I need to do to return the output?

Answer 1

You need to use the option shell=True in Popen() to have pipes work.

Note that if you don’t know exactly where the Popen input is coming from, then shell=True is a security risk.

Also, you don’t need to split bashCommand here. For example:

>>> import subprocess as sp    
>>> cmd = 'echo "test" | cat'
>>> process = sp.Popen(cmd,stdout=sp.PIPE,shell=True)
>>> output = process.communicate()[0]
>>> print output
test