docopt-sh 0.9.16

docopt.sh - Bash argument parser generator.

docopt uses your help text to parse command-line arguments for you. It is available in many different languages, this implementation is for bash 3.2, 4+, and 5+.

• Introduction

  • How it works

  • Installation

  • Quick example

  • Refreshing the parser

  • Parser output

• Advanced usage

  • Commandline options

  • Parser options

  • Exiting with a usage message

  • Library mode

  • On-the-fly parser generation

• Developers

  • Testing

How it works

Given a script docopt.sh finds the docopt (DOC="...") help text, parses it, generates a matching parser in bash, and then inserts it back into the original script. The patched script will have no dependencies and can be shipped as a single file.

To reduce the amount of code added to the it, the script will only contain a parser made for that specific help text. For that reason there is no need for the generator itself to be written in bash, instead that part is written in Python 3. Though, this also means that you have to regenerate your parser every time you change the help text (see On-the-fly parser generation for automating that part while developing).

Installation

Install docopt.sh using pip:

sudo pip3 install docopt-sh

Quick example

Here is an abbreviated version of Naval Fate.

#!/usr/bin/env bash
DOC="Naval Fate.
Usage:
  naval_fate.sh ship <name> move <x> <y> [--speed=<kn>]
  naval_fate.sh ship shoot <x> <y>

Options:
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine."
naval_fate() {
  eval "$(docopt "$@")"
  $ship && $move && printf "The %s is now moving to %d,%d at %d knots.\n" "$_name_" "$_x_" "$_y_" "$__speed"
  $ship && $shoot && printf "You shoot at %d,%d. It's a hit!\n" "$_x_" "$_y_"
  return 0
}
naval_fate "$@"

We can use docopt.sh to insert a matching parser:

$ docopt.sh naval_fate.sh
naval_fate.sh has been updated

The file will now look like this:

#!/usr/bin/env bash
DOC="Naval Fate.
Usage:
  naval_fate.sh ship <name> move <x> <y> [--speed=<kn>]
  naval_fate.sh ship shoot <x> <y>

Options:
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine."
# docopt parser below, refresh this parser with `docopt.sh naval_fate.sh`
# shellcheck disable=2016
docopt() { docopt_run() { docopt_doc=${DOC:0:237}; docopt_usage=${DOC:13:97}
docopt_digest=79f25; docopt_shorts=(''); docopt_longs=(--speed)
... more code ...
done; if ! docopt_required "$root_idx" || [ ${#docopt_left[@]} -gt 0 ]; then
docopt_error; fi; return 0; }
# docopt parser above, complete command for generating this parser is `docopt.sh naval_fate.sh`
naval_fate() {
  eval "$(docopt "$@")"
  $ship && $move && printf "The %s is now moving to %d,%d at %d knots.\n" "$_name_" "$_x_" "$_y_" "$__speed"
  $ship && $shoot && printf "You shoot at %d,%d. It's a hit!\n" "$_x_" "$_y_"
  return 0
}
naval_fate "$@"

To try it out we run naval_fate.sh

$ ./naval_fate.sh ship Olympia move 1 5 --speed 8
The Olympia is now moving to 1,5 at 8 knots.

The variables $ship, $move, etc. are not set globally, but rather contained to the scope of the invoking function. You are however not restricted to calling eval "$(docopt "$@")" from a function, calling docopt outside of functions will work just as well and the variables will then be defined globally.

Refreshing the parser

docopt.sh embeds a shasum of the help text into the parser to ensure that the two always match. In order to update the parser, simply run docopt.sh again. The existing parser will be replaced with a new one. If the parser was generated with any particular options, these options will be re-applied unless instructed otherwise with --no-auto-params.

$ docopt.sh --line-length 120 naval_fate.sh
naval_fate.sh has been updated.
$ docopt.sh naval_fate.sh
Adding `--line-length=120` from parser generation parameters that were detected
in the script. Use --no-auto-params to disable this behavior.
The parser in naval_fate.sh is already up-to-date.

Once you have generated the parser, you can move the codeblock to any other place in your script. The script patcher will automatically find the codeblock and replace it with an updated version.

In order to avoid “works on my machine” issues, the parser automatically skips the help text check on machines without shasum or sha256sum (a “command not found” error will still be printed though). The check can also manually be disabled with $DOCOPT_DOC_CHECK (see parser options for more on that).

Parser output

Names of arguments, commands, and options are mapped by replacing everything that is not an alphanumeric character with an underscore. This means --speed becomes $__speed, -f becomes $_f, and <name> becomes _name_, while NAME stays as $NAME and set stays as $set.

Switches (options without arguments) and commands become true or false. If a switch or command can be specified more than once, the resulting variable value will be an integer that has been incremented the number of times the parameter was specified.

Options with values and regular arguments become strings. If an option with a value or an argument can be specified more than once, the value will be an array of strings.

To clarify, given this (somewhat complex, but concise) doc and invocation:

Usage:
  program -v... -s --val=VAL multicmd... command ARG ARGS...

$ program -vvv -s --val XY multicmd multicmd command A 1 2 3

The variables and their values will be:

_v=3 # -vvv
_s=true # -s
__val=XY # --val XY
multicmd=2 # multicmd multicmd
command=true # command
ARG=A # A
ARGS=(1 2 3) # 1 2 3

You can use $DOCOPT_PREFIX to prefix the above variable names with a custom string (e.g. specifying DOCOPT_PREFIX=prog would change ARG to progARG). See parser options for additional parser options.

Commandline options

The commandline options of docopt.sh only change how the parser is generated, while global variables specified before eval "$(docopt "$@")" itself change the behavior of the parser.

The commandline options are:

Option	Description
--line-length -n N	Max line length when minifying. Disable with 0 (default: 80)
--library -l SRC	Generates the dynamic part of the parser and includes the static parts with source SRC.
--no-auto-params -P	Disable auto-detection of parser generation parameters.
--parser -p	Output the parser instead of inserting it in the script.
--help -h	Show the help screen.
--version	Show docopt.sh version.

Parser options

Parser options change the behavior of the parser in various ways. These options are specified as global variables and must be specified before invoking eval "$(docopt "$@")". You do not need to regenerate the parse when changing any of these options.

Option	Description
$DOCOPT_PROGRAM_VERSION	The string to print when –version is specified (default: none)
$DOCOPT_ADD_HELP	Set to false to not print usage on –help (default: true)
$DOCOPT_OPTIONS_FIRST	Set to true to treat everything after the first non-option as commands/arguments (default: false)
$DOCOPT_PREFIX	Prefixes all variable names with the specified value (default: "")
$DOCOPT_DOC_CHECK	Set to false to disable checking whether the parser matches the doc (default: true)
$DOCOPT_LIB_CHECK	Set to false to disable checking whether the library version and the docopt parser version match (default: true)

Exiting with a usage message

Oftentimes additional verification of parameters is necessary (e.g. when an option value is an enum). In those cases you can use docopt_exit "message" in order to output a message for the user, the function automatically appends a short usage message (i.e. the Usage: part of the doc) and then exits with code 1.

Note that this function is only defined after you have run eval "$(docopt "$@")", it is part of the docopt output.

Library mode

Instead of inlining the entirety of the parser in your script, you can move the static parts to an external file and only insert the dynamic part into your script. This is particularly useful when you have multiple bash scripts in the same project that use docopt.sh. To generate the library run docopt.sh generate-library > DEST. The output is written to stdout, so make sure to add that redirect.

Once a library has been generated you can insert the dynamic part of your parser into your script with docopt.sh --library DEST SCRIPT. The generator will then automatically add a source DEST to the parser. Make sure to quote your library path if it contains spaces like so docopt.sh --library '"/path with spaces/docopt-lib.sh"'. You do not need to specify --library on subsequent refreshes of the parser, docopt.sh will automatically glean the previously used parameters from your script and re-apply them.

--library can be any valid bash expression, meaning you can use things like "$(dirname "$0")".

On every invocation docopt checks that the library version and the version of the dynamic part in the script match. The parser exits with an error if that is not the case.

On-the-fly parser generation

ATTENTION: The method outlined below relies on docopt.sh being installed and is only intended for development use, do not release any scripts that use this method.

When developing a new script you might add, modify, and remove parameters quite often. Having to refresh the parser with every change can quickly become cumbersome and interrupt your workflow. To avoid this you can use the --parser flag to generate and then immediately eval the output in your script before invoking eval "$(docopt "$@")".

The script from the introduction would look like this (only eval "$(docopt.sh --parser "$0")" has been added):

#!/usr/bin/env bash
DOC="Naval Fate.
Usage:
  naval_fate.sh ship <name> move <x> <y> [--speed=<kn>]
  naval_fate.sh ship shoot <x> <y>

Options:
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine."
naval_fate() {
  eval "$(docopt.sh --parser "$0")"
  eval "$(docopt "$@")"
  $ship && $move && printf "The %s is now moving to %d,%d at %d knots.\n" "$_name_" "$_x_" "$_y_" "$__speed"
  $ship && $shoot && printf "You shoot at %d,%d. It's a hit!\n" "$_x_" "$_y_"
  return 0
}
naval_fate "$@"

Since docopt.sh is not patching the script, you also avoid any line number jumps in your IDE. However, remember to replace this with the proper parser before you ship the script.

Developers

Testing

docopt.sh uses pytest for testing. You can run the testsuite by executing pytest in the root of the project.

All use cases from the original docopt are used to validate correctness. Per default pytest uses the bash version that is installed on the system to run the tests. However, you can specify multiple alternate versions using --bash-version <versions>, where <versions> is a comma-separated list of bash versions (e.g. 3.2,4.0,4.1). These versions need to be downloaded and compiled first, which you can do with get_bash.py. The script downloads, extracts, configures, and compiles the specified bash versions in the tests/bash-versions folder. Use --bash-version all to test with all the bash versions that are installed.