CODEWITHSUNDEEP
python
kshenoy
kshenoy

Reputation: 1826

Running shell command from Python script

I'm trying to run a shell command from within a python script which needs to do several things
1. The shell command is 'hspice tran.deck >! tran.lis'
2. The script should wait for the shell command to complete before proceeding
3. I need to check the return code from the command and
4. Capture STDOUT if it completed successfully else capture STDERR

I went through the subprocess module and tried out a couple of things but couldn't find a way to do all of the above.
- with subprocess.call() I could check the return code but not capture the output.
- with subprocess.check_output() I could capture the output but not the code.
- with subprocess.Popen() and Popen.communicate(), I could capture STDOUT and STDERR but not the return code.
I'm not sure how to use Popen.wait() or the returncode attribute. I also couldn't get Popen to accept '>!' or '|' as arguments.

Can someone please point me in the right direction? I'm using Python 2.7.1

EDIT: Got things working with the following code 

process = subprocess.Popen('ls | tee out.txt', shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = process.communicate()
if(process.returncode==0):
  print out
else:
  print err

Also, should I use a process.wait() after the process = line or does it wait by default?

Upvotes: 4

Views: 8871

Answers (3)

Niklas B.
Niklas B.

Reputation: 95358

Just use .returncode after .communicate(). Also, tell Popen that what you're trying to run is a shell command, rather than a raw command line:

p = subprocess.Popen('ls | tee out.txt', shell=True, ...)
p.communicate()
print p.returncode

Upvotes: 10

Adam
Adam

Reputation: 2361

Here is example how to interact with shell:

>>> process = subprocess.Popen(['/bin/bash'], shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
>>> process.stdin.write('echo it works!\n')
>>> process.stdout.readline()
'it works!\n'
>>> process.stdin.write('date\n')
>>> process.stdout.readline()
'wto, 13 mar 2012, 17:25:35 CET\n'
>>>

Upvotes: -1

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 799490

From the docs:

Popen.returncode

The child return code, set by poll() and wait() (and indirectly by communicate()). A None value indicates that the process hasn’t terminated yet.

A negative value -N indicates that the child was terminated by signal N (Unix only).

Upvotes: 3

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