Can I have subprocess.call write the output of the call to a string?

Question

I want to do subprocess.call, and get the output of the call into a string. Can I do this directly, or do I need to pipe it to a file, and then read from it?

In other words, can I somehow redirect stdout and stderr into a string?

Answer 1

This is an extension of mantazer's answer to python3. You can still use the subprocess.check_output command in python3:

>>> subprocess.check_output(["echo", "hello world"])
b'hello world\n'

however now it gives us a byte string. To get a real python string we need to use decode:

>>> subprocess.check_output(["echo", "hello world"]).decode(sys.stdout.encoding)
'hello world\n'

Using sys.stdout.encoding as the encoding rather than just the default UTF-8 should make this work on any OS (at least in theory).

The trailing newline (and any other extra whitespace) can be easily removed using .strip(), so the final command is:

>>> subprocess.check_output(["echo", "hello world"]
                            ).decode(sys.stdout.encoding).strip()
'hello world'

Answer 2

No, you can't read the output of subprocess.call() directly into a string.

In order to read the output of a command into a string, you need to use subprocess.Popen(), e.g.:

>>> cmd = subprocess.Popen('ls', stdout=subprocess.PIPE)
>>> cmd_out, cmd_err = cmd.communicate()

cmd_out will have the string with the output of the command.