failprint

Run a command, print its output only if it fails.

Tired of searching the quiet options of your programs to lighten up the output of your make check or make lint commands?

Tired of finding out that standard output and error are mixed up in some of them?

Simply run your command through failprint. If it succeeds, nothing is printed. If it fails, standard error is printed. Plus other configuration goodies 😉

Example

You don't want to see output when the command succeeds.

The task runner duty uses failprint, allowing you to define tasks in Python and run them with minimalist and beautiful output:

Requirements

failprint requires Python 3.8 or above.

To install Python 3.8, I recommend using pyenv.

# install pyenv
git clone https://github.com/pyenv/pyenv ~/.pyenv

# setup pyenv (you should also put these three lines in .bashrc or similar)
export PATH="${HOME}/.pyenv/bin:${PATH}"
export PYENV_ROOT="${HOME}/.pyenv"
eval "$(pyenv init -)"

# install Python 3.8.17
pyenv install 3.8.17

# make it available globally
pyenv global system 3.8.17

Installation

pip install failprint

With uv:

uv tool install failprint

Usage

% poetry run failprint -h
usage: failprint [-h] [-c {stdout,stderr,both,none}] [-f {pretty,tap}] [-y | -Y] [-p | -P] [-q | -Q] [-s | -S] [-z | -Z] [-n NUMBER]
                 [-t TITLE]
                 COMMAND [COMMAND ...]

positional arguments:
  COMMAND

optional arguments:
  -h, --help            show this help message and exit
  -c {stdout,stderr,both,none}, --capture {stdout,stderr,both,none}
                        Which output to capture. Colors are supported with 'both' only, unless the command has a 'force color'
                        option.
  -f {pretty,tap}, --format {pretty,tap}
                        Output format. Pass your own Jinja2 template as a string with '-f custom=TEMPLATE'. Available variables:
                        command, title (command or title passed with -t), code (exit status), success (boolean), failure (boolean),
                        number (command number passed with -n), output (command output), nofail (boolean), quiet (boolean), silent
                        (boolean). Available filters: indent (textwrap.indent).
  -y, --pty             Enable the use of a pseudo-terminal. PTY doesn't allow programs to use standard input.
  -Y, --no-pty          Disable the use of a pseudo-terminal. PTY doesn't allow programs to use standard input.
  -p, --progress        Print progress while running a command.
  -P, --no-progress     Don't print progress while running a command.
  -q, --quiet           Don't print the command output, even if it failed.
  -Q, --no-quiet        Print the command output when it fails.
  -s, --silent          Don't print anything.
  -S, --no-silent       Print output as usual.
  -z, --zero, --nofail  Don't fail. Always return a success (0) exit code.
  -Z, --no-zero, --strict
                        Return the original exit code.
  -n NUMBER, --number NUMBER
                        Command number. Useful for the 'tap' format.
  -t TITLE, --title TITLE
                        Command title. Default is the command itself.

from failprint.runners import run

cmd = "echo hello"

exit_code = run(
    cmd,            # str, list of str, or Python callable
    args=None,      # args for callable
    kwargs=None,    # kwargs for callable
    number=1,       # command number, useful for tap format
    capture=None,   # stdout, stderr, both, none, True or False
    title=None,     # command title
    fmt=None,       # pretty, tap, or custom="MY_CUSTOM_FORMAT"
    pty=False,      # use a PTY
    progress=True,  # print the "progress" template before running the command
    nofail=False,   # always return zero
    quiet=False,    # don't print output when the command fails
    silent=False,   # don't print anything
)