Question

I can not get the subprocess.call() to work properly:

>>> from subprocess import call
>>> call(['adduser', '--home=/var/www/myusername/', '--gecos', 'GECOS', '--disabled-login', 'myusername'], shell=True)
adduser: Only one or two names allowed.
1

But without shell=True:

>>> call(['adduser', '--home=/var/www/myusername/', '--gecos', 'GECOS', '--disabled-login', 'myusername'])
Adding user `myusername' ...
Adding new group `myusername' (1001) ...
Adding new user `myusername' (1001) with group `myusername' ...
Creating home directory `/var/www/myusername/' ...
Copying files from `/etc/skel' ...
0

Or the same directly in shell:

root@www1:~# adduser --home=/var/www/myusername/ --gecos GECOS --disabled-login myusername
Adding user `myusername' ...
Adding new group `myusername' (1001) ...
Adding new user `myusername' (1001) with group `myusername' ...
Creating home directory `/var/www/myusername/' ...
Copying files from `/etc/skel' ...

I miss some logic in the shell=True behavior. Can somebody explain me why? What is wrong with the first example? From the adduser command error message it seems that arguments are somehow crippled.

Thanks!

Answer 1

When you specify shell=True you switch to quite different behaviour. From the docs:

On Unix with shell=True, the shell defaults to /bin/sh. If args is a
string, the string specifies the command to execute through the shell.
This means that the string must be formatted exactly as it would be
when typed at the shell prompt. This includes, for example, quoting or
backslash escaping filenames with spaces in them. If args is a
sequence, the first item specifies the command string, and any
additional items will be treated as additional arguments to the shell
itself. That is to say, Popen does the equivalent of:

Popen([‘/bin/sh’, ‘-c’, args[0], args[1], …])

So you are running the equivalent of

/bin/sh -c "adduser" --home=/var/www/myusername/ --gecos GECOS --disabled-login myusername

The error message you are getting is what happens when you try and run adduser without any arguments as all the arguments are being passed to sh.

If you want to set shell=True then you would need to call it like this:

call('adduser --home=/var/www/myusername/ --gecos GECOS --disabled-login myusername', shell=True)

OR like this:

call(['adduser --home=/var/www/myusername/ --gecos GECOS --disabled-login myusername'], shell=True)

But mostly you just want to use call without the shell=True and use a list of arguments. As per your second, working, example.