def pid(sig):
    '''
    Return the PID or an empty string if the process is running or not.
    Pass a signature to use to find the process via ps.  Note you can pass
    a Python-compatible regular expression to return all pids of
    processes matching the regexp.

    .. versionchanged:: 2016.11.4
        Added support for AIX

    CLI Example:

    .. code-block:: bash

        salt '*' status.pid <sig>
    '''

    cmd = __grains__['ps']
    output = __salt__['cmd.run_stdout'](cmd, python_shell=True)

    pids = ''
    for line in output.splitlines():
        if 'status.pid' in line:
            continue
        if re.search(sig, line):
            if pids:
                pids += '\n'
            pids += line.split()[1]

    return pids