Skip to content


milpa help docs milpa command

milpa runs your scripts or executables, by matching passed arguments to files in .milpa/commands directories. It looks at a few of these, starting with the one where milpa was called from. Check out MILPA_PATH of milpa help docs milpa environment to understand where milpa looks for commands. A collection of commands under a single .milpa folder is called a repo, and you can learn more reading milpa help docs milpa repo

Your script or executable plus its corresponding spec is what we call a milpa command. Scripts can be:

  1. bash scripts, with an .sh extension, or
  2. executable files without an extension, written in whatever language you want. If your command does not have an extension, remember to set on the executable bit (chmod +x .milpa/commands/your-command)!


A spec is a file named just like your script, except with a .yaml extension, with a few basic details about what your command does and what kinds of input it deals with. There's more details at milpa help docs milpa command spec, but here's a brief example:

# .milpa/commands/greet.yaml
summary: a very well mannered program
description: greets you politely on stdout
  - name: full-name
    description: the name to greet
    variadic: true
    default: Quihúbole mi
    description: the greeting word to use


A script then, will be able to use the definitions from your spec and do fun stuff with them, for example:

#!/bin/env bash
# .milpa/commands/
function title_case() {
  set ${*,,}
  echo ${*^}

# arguments are passed as environment variables
if [[ "${#MILPA_ARG_FULL_NAME}" -eq  0 ]]; then

# and so are options!
echo "$MILPA_OPT_GREETING $(title_case "$name")"

Arguments, Options and Environment

The arguments and options passed in the command line will be parsed and validated according to your spec. If valid, your script will receive numbered arguments as usual ($1 and so on), excluding any supplied options (i.e. without --option=value "arguments"). Valid arguments and options will be available to your script as environment variables as well.

⚠️ Unknown arguments and options will cause an error before your script executes!

The environment available to a script is composed of four groups:

  1. MILPA_COMMAND_* variables have information about the command called by the user,
  2. MILPA_ARG_* variables hold values for every argument of the spec,
  3. MILPA_OPT_* variables hold values for every option defined, and
  4. global environment variables that affect milpa's overall behavior.

ℹ️ variadic arguments and repeated options are passed an array of values (i.e. read with ${MILPA_OPT_THING[@]})

Command metadata: MILPA_COMMAND_*

Your script has access to the following variables set by milpa after parsing arguments and running validations:

Arguments: MILPA_ARG_*

Arguments specified on your spec will show up as environment variables with the MILPA_ARG_ prefix, followed by the name set in your spec. Names will be all uppercase, and dashes will be turned into underscores. See the command spec for more information on arguments, and this abbreviated example below:

# when ran like this:
milpa greet
# would output:
#> Quihúbole mi Grace

# you can also pass a specific name to greet, overriding the default
milpa greet elmer homero
# would output:
#> Quihúbole mi Elmer Homero

Options: MILPA_OPT_*

Options show up on the environment with the MILPA_OPT_ prefix followed by the name in your spec. Names will be all uppercase, and dashes will be turned into underscores. In the command spec you'll find more details on how to define options.

# when ran like this:
milpa greet --greeting Sup
# would output:
#> Sup Grace

# you can also pass a specific name to greet, overriding the default
milpa greet --greeting Oi joão
# would output:
#> Oi João

Boolean type options have a special behavior, their value will be an empty string ("") if false, and "true" if true, so comparing them in bash is simpler (i.e. if [[ "$MILPA_OPT_BOOL_FLAG" ]] ), for example:

# let's add options to the example above
    type: boolean
    default: false
# we modify the example above
if [[ "$MILPA_OPT_SHOUT" ]]; then
  echo "$MILPA_OPT_GREETING $(title_case "$name")!" | awk '{print toupper($0)}'
  echo "$MILPA_OPT_GREETING $(title_case "$name")"
# and run with
milpa greet --shout loud boi
# to get