Pipe subprocess standard output to a variable [duplicate]

To get the output of ls, use stdout=subprocess.PIPE.

>>> proc = subprocess.Popen('ls', stdout=subprocess.PIPE)>>> output = proc.stdout.read()>>> print outputbarbazfoo

The command cdrecord --help outputs to stderr, so you need to pipe that indstead. You should also break up the command into a list of tokens as I've done below, or the alternative is to pass the shell=True argument but this fires up a fully-blown shell which can be dangerous if you don't control the contents of the command string.

>>> proc = subprocess.Popen(['cdrecord', '--help'], stderr=subprocess.PIPE)>>> output = proc.stderr.read()>>> print outputUsage: wodim [options] track1...tracknOptions:    -version    print version information and exit    dev=target  SCSI target to use as CD/DVD-Recorder    gracetime=# set the grace time before starting to write to #....

If you have a command that outputs to both stdout and stderr and you want to merge them, you can do that by piping stderr to stdout and then catching stdout.

subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)

As mentioned by Chris Morgan, you should be using proc.communicate() instead of proc.read().

>>> proc = subprocess.Popen(['cdrecord', '--help'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)>>> out, err = proc.communicate()>>> print 'stdout:', outstdout: >>> print 'stderr:', errstderr:Usage: wodim [options] track1...tracknOptions:    -version    print version information and exit    dev=target  SCSI target to use as CD/DVD-Recorder    gracetime=# set the grace time before starting to write to #....

If you are using python 2.7 or later, the easiest way to do this is to use the subprocess.check_output() command. Here is an example:

output = subprocess.check_output('ls')

To also redirect stderr you can use the following:

output = subprocess.check_output('ls', stderr=subprocess.STDOUT)

In the case that you want to pass parameters to the command, you can either use a list or use invoke a shell and use a single string.

output = subprocess.check_output(['ls', '-a'])output = subprocess.check_output('ls -a', shell=True)

With a = subprocess.Popen("cdrecord --help",stdout = subprocess.PIPE), you need to either use a list or use shell=True;

Either of these will work. The former is preferable.

a = subprocess.Popen(['cdrecord', '--help'], stdout=subprocess.PIPE)a = subprocess.Popen('cdrecord --help', shell=True, stdout=subprocess.PIPE)

Also, instead of using Popen.stdout.read/Popen.stderr.read, you should use .communicate() (refer to the subprocess documentation for why).

proc = subprocess.Popen(['cdrecord', '--help'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)stdout, stderr = proc.communicate()