Pipe error with bash script called from python

Question

I'm trying to run a shell script inside some python code, but I keep getting an error message.

Python script (test.py):

   import os
    f = os.popen('/home/test/Downloads/record.sh')
    f.close()

Shell script (record.sh):

#!/bin/sh
rec -r 16k -c 1 -p | sox -p output.wav silence 1 0.1 1% -1 0.5 1% &

When I run:

python test.py

This is the error message that I get: FAIL sox: `-' error writing output file: Broken pipe

Running the shell script alone works fine (i.e. ./record.sh).

What am I doing wrong? Thanks.

EDIT BELOW: I have changed the shell script, so it looks like this (there is no longer any piping):

#!/bin/sh
rec -r 16k -b 16 -c 1 output.wav silence 1 0.5 0.1% 1 1.0 0.1%

With Stefano's help I have the following Python script:

#!/usr/bin/python
from subprocess import Popen, PIPE
output = Popen(["sh", "/home/test/Downloads/data/recorder.sh", ], stdout=PIPE).communicate()[0]

Do I still need the PIPE and communicate bits?

What do I need to change, so that the python script doesn't wait for recorder.sh to finish before moving on?

Answer 1

To run a shell script in python 2.6, use the commands module:

import commands
status, output = commands.getstatusoutput("./script.sh")

status is now the exist status of your program, hopefully 0. The output the same as if the script were run like this:

{ cmd ; } 2>&1

In python3, the getstatusoutput method has moved into subprocess,

import subprocess
status, output = subprocess.getstatusoutput("./script.sh")

Please refer to:

• subprocess
• commands

In the standard library documentation.

There are more ways to spawn subprocesses, and you need to assess which one is the correct method in your case. Refer to the subprocess docs to read about them.

An even better way to run your script is this:

from subprocess import Popen, PIPE
output = Popen(["sh", "script.sh", ], stdout=PIPE).communicate()[0]

It will work in python 2.6, 2.7, 3.1 and 3.2.

Note though that you can not use shell script in this method, if you want to pipe output around, use this method instead:

p1 = Popen(["dmesg"], stdout=PIPE)
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
output = p2.communicate()[0]

Whereas the commands module will accept "dmesg | grep hda"