naval_fate.sh

Run docopt.sh to insert a parser that matches the helptext into the script:

See the patched file here

Note that the script is completely independent from the python package.
docopt.sh is merely a development tool to insert and update the parser, your scripts will be entirely self contained.
The parser is inlined right beneath the DOC="…​" and takes up ~110 lines of code (depending on the size of your helptext). If you ship multiple scripts in the same project you can reduce that to ~20 lines by moving the generic parts of the parser to a different file and reusing it.

Introduction

• Quick start

• Installation

• How it works

• Local vs. global variables

• 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

Install docopt.sh using pip:

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).

Local vs. global variables

docopt_exit() { [[ -n $1 ]] && printf "%s\n" "$1" >&2
printf "%s\n" "${DOC:12:87}" >&2; exit 1; }
declare -- __speed="10"
declare -- _name_=""
declare -- _x_="1"
declare -- _y_="5"
declare -- move="false"
declare -- shoot="true"

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.

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).

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:

The variables and their values will be:

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.

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:

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.

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.

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.

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):

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.

Testing