ubelt.util_cmd module

This module exposes the ubelt.cmd command, which provides a simple means for interacting with the commandline. While this does use subprocess.Popen under the hood, the key draw of ubelt.cmd is that you can capture stdout/stderr in your program while simultaneously printing it to the terminal in real time.


>>> import ubelt as ub
>>> # Running with verbose=1 will write to stdout in real time
>>> info = ub.cmd('echo "write your command naturally"', verbose=1)
write your command naturally
>>> # Unless `detatch=True`, `cmd` always returns an info dict.
>>> print('info = ' + ub.repr2(info))
info = {
    'command': 'echo "write your command naturally"',
    'cwd': None,
    'err': '',
    'out': 'write your command naturally\n',
    'proc': <subprocess.Popen object at ...>,
    'ret': 0,
ubelt.util_cmd.cmd(command, shell=False, detach=False, verbose=0, tee=None, cwd=None, env=None, tee_backend='auto', verbout=None, **kwargs)[source]

Executes a command in a subprocess.

The advantage of this wrapper around subprocess is that (1) you control if the subprocess prints to stdout, (2) the text written to stdout and stderr is returned for parsing, (3) cross platform behavior that lets you specify the command as a string or tuple regardless of whether or not shell=True. (4) ability to detach, return the process object and allow the process to run in the background (eventually we may return a Future object instead).

  • command (str or Sequence) – bash-like command string or tuple of executable and args
  • shell (bool) – if True, process is run in shell, defaults to False.
  • detach (bool) – if True, process is detached and run in background, defaults to False.
  • verbose (int) – verbosity mode. Can be 0, 1, 2, or 3. Defaults to 0.
  • tee (bool, optional) – if True, simultaneously writes to stdout while capturing output from the command. If not specified, defaults to True if verbose > 0. If detech is True, then this argument is ignored.
  • cwd (PathLike, optional) – path to run command
  • env (str, optional) – environment passed to Popen
  • tee_backend (str, optional) – backend for tee output. Valid choices are: “auto”, “select” (POSIX only), and “thread”.
  • **kwargs – only used to support deprecated arguments

info - information about command status.

if detach is False info contains captured standard out, standard error, and the return code if detach is False info contains a reference to the process.

Return type:



Inputs can either be text or tuple based. On UNIX we ensure conversion to text if shell=True, and to tuple if shell=False. On windows, the input is always text based. See [3] for a potential cross-platform shlex solution for windows.

python -m ubelt.util_cmd cmd python -c “import ubelt as ub; ub.cmd(‘ping localhost -c 2’, verbose=2)”


[1] https://stackoverflow.com/questions/11495783/redirect-subprocess-stderr-to-stdout [2] https://stackoverflow.com/questions/7729336/how-can-i-print-and-display-subprocess-stdout-and-stderr-output-without-distorti [3] https://stackoverflow.com/questions/33560364/python-windows-parsing-command-lines-with-shlex


>>> info = cmd(('echo', 'simple cmdline interface'), verbose=1)
simple cmdline interface
>>> assert info['ret'] == 0
>>> assert info['out'].strip() == 'simple cmdline interface'
>>> assert info['err'].strip() == ''
>>> info = cmd('echo str noshell', verbose=0)
>>> assert info['out'].strip() == 'str noshell'
>>> # windows echo will output extra single quotes
>>> info = cmd(('echo', 'tuple noshell'), verbose=0)
>>> assert info['out'].strip().strip("'") == 'tuple noshell'
>>> # Note this command is formatted to work on win32 and unix
>>> info = cmd('echo str&&echo shell', verbose=0, shell=True)
>>> assert info['out'].strip() == 'str' + chr(10) + 'shell'
>>> info = cmd(('echo', 'tuple shell'), verbose=0, shell=True)
>>> assert info['out'].strip().strip("'") == 'tuple shell'
>>> import ubelt as ub
>>> from os.path import join, exists
>>> fpath1 = join(ub.get_app_cache_dir('ubelt'), 'cmdout1.txt')
>>> fpath2 = join(ub.get_app_cache_dir('ubelt'), 'cmdout2.txt')
>>> ub.delete(fpath1)
>>> ub.delete(fpath2)
>>> info1 = ub.cmd(('touch', fpath1), detach=True)
>>> info2 = ub.cmd('echo writing2 > ' + fpath2, shell=True, detach=True)
>>> while not exists(fpath1):
...     pass
>>> while not exists(fpath2):
...     pass
>>> assert ub.readfrom(fpath1) == ''
>>> assert ub.readfrom(fpath2).strip() == 'writing2'
>>> info1['proc'].wait()
>>> info2['proc'].wait()