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POredirecting shell output using subprocess
 

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    <p>I have a python script which calls a lot of shell functions. The script can be run interactively from a terminal, in which case I'd like to display output right away, or called by crontab, in which case I'd like to email error output.</p> <p>I wrote a helper function for calling shell functions:</p> <pre><code>import subprocess import shlex import sys def shell(cmdline, interactive=True): args = shlex.split(cmdline.encode("ascii")) proc = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE) val = proc.communicate() if interactive is True: if proc.returncode: print "returncode " + str(proc.returncode) print val[1] sys.exit(1) else: print val[0] else: if proc.returncode: print "" # send email with val[0] + val[1] if __name__ == "__main__": # example of command that produces non-zero returncode shell("ls -z") </code></pre> <p>The problem I'm having is two-fold.</p> <p>1) In interactive mode, when the shell command takes a while to finish (e.g. few minutes), I don't see anything until the command is completely done since communicate() buffers output. Is there a way to display output as it comes in, and avoid buffering? I also need a way to check the returncode, which is why I'm using communicate().</p> <p>2) Some shell commands I call can produce a lot of output (e.g. 2MB). The <a href="http://docs.python.org/library/subprocess.html#subprocess.Popen.communicate" rel="nofollow">documentation</a> for communicate() says "do not use this method if the data size is large or unlimited." Does anyone know how large is "large"?</p>
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