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An elegant option parser for shell scripts (full support for all POSIX shells)

getoptions is a new option parser and generator written in POSIX-compliant shell script and released in august 2020. It is for those who want to support the POSIX / GNU style option syntax in your shell scripts. Most easy, simple, fast, small, extensible and portable. No more any loops and templates needed!




parser_definition() {
  setup   REST help:usage -- "Usage: [options]... [arguments]..." ''
  msg -- 'Options:'
  flag    FLAG    -f --flag                 -- "takes no arguments"
  param   PARAM   -p --param                -- "takes one argument"
  option  OPTION  -o --option on:"default"  -- "takes one optional argument"
  disp    :usage  -h --help
  disp    VERSION    --version

eval "$(getoptions parser_definition) exit 1"

printf '%s\n' "$@" # rest arguments

It generates a simple option parser code internally and parses the following arguments. -f --flag -p VALUE --param VALUE -o --option -oVALUE --option=VALUE 1 2 3
$ --help

Usage: [options]... [arguments]...

  -f, --flag                  takes no arguments
  -p, --param PARAM           takes one argument
  -o, --option[=OPTION]       takes one optional argument
  -h, --help

Table of Contents


  • Full support for all POSIX shells, no limitations, no bashisms
  • High portability, supports all platforms (Linux, macOS, Windows, etc) where works POSIX shells
  • Neither getopt nor getopts is used, and implemented with shell scripts only
  • Provides DSL-like shell script way to define parsers for flexibility and extensibility
  • No need for code generation from embedded special comments
  • Can be used as an option parser generator to run without getoptions
  • Support for POSIX [1] and GNU [2] [3] compliant option syntax
  • Support for long options
  • Support for subcommands
  • Support for abbreviation option
  • Support for automatic help generation
  • Support for options to call action function
  • Support for validation and custom error handler
  • Works fast with small overhead and small file size (5KB - 8KB) library
  • No global variables are used (except the special variables OPTARG and OPTIND)
  • Only a minimum of one (and a maximum of three) global functions are defined as a library
  • No worry about license, it's public domain (Creative Commons Zero v1.0 Universal)

getopt vs getopts vs getoptions

getopt getopts getoptions
Implementation external command shell builtin command shell script
Portability No Yes Yes
Short option beginning with - ✔️ ✔️ ✔️
Short option beginning with + zsh, ksh, mksh only ✔️
Combining short options ✔️ ✔️ ✔️
Long option beginning with -- GNU only ✔️
Long option beginning with - GNU only ✔️ limited
Abbreviating long options GNU only ✔️
Optional argument GNU only ✔️
Option after arguments GNU only ✔️
Stop option parsing with -- ✔️ ✔️ ✔️
Scanning modes GNU only ✔️ + and enhancement
Subcommand ✔️
Validation by pattern matching ✔️
Custom validation ✔️
Custom error handler ✔️ ✔️ more flexible
Automatic help generation ✔️


Almost no requirements.

  • Any POSIX shells
    • dash 0.5.4+, bash 2.03+, ksh 88+, mksh R28+, zsh 3.1.9+, yash 2.29+, busybox ash 1.1.3+, etc
  • Only cat is used for help display, but it can be removed


Download prebuild shell scripts from releases.

  • getoptions: Option parser
  • gengetoptions: Option parser generator
wget -O $HOME/bin/getoptions
chmod +x $HOME/bin/getoptions

# optional
wget -O $HOME/bin/gengetoptions
chmod +x $HOME/bin/gengetoptions

Or build and install it yourself.

git clone
cd getoptions
make install PREFIX=$HOME

Homebrew / Linuxbrew

brew tap ko1nksm/getoptions
brew install getoptions


Support three ways of use. It is better to use it as a command at first, and then use it as a library or generator as needed.

command library generator
easy ★★★ ★★☆ ★☆☆
fast ★☆☆ ★★☆ ★★★

Use as a command

Use the getoptions command that you installed on your system. This assumes that you have the getoptions command installed, but it is the easiest to use and is suitable for personal scripts.

The execution speed is slightly slower than using it as a library. (Approx. 15ms overhead)

parser_definition() {
  setup REST help:usage -- "Usage: [options]... [arguments]..."

eval "$(getoptions parser_definition parse) exit 1"
parse "$@"
eval "set -- $REST"

The above code exit 1 is the recommended option. This allows you to exit if the getoptions command is not found.

If you omit the option parser name or use -, it will define the default option parser and parse arguments immediately.

parser_definition() {
  setup REST help:usage -- "Usage: [options]... [arguments]..."

eval "$(getoptions parser_definition) exit 1"

# The above means the same as the following code.
# eval "$(getoptions parser_definition getoptions_parse) exit 1"
# getoptions_parse "$@"
# eval "set -- $REST"

HINT: Are you wondering why the external command can call a shell function?

The external command getoptions will output the shell function getoptions. The external command getoptions will be hidden by the shell function getoptions that defined by eval, and the getoptions will be called again, so it can be call the shell function parser_definition.

Try running the following command to see what is output.

$ getoptions parser_definition parse

Use as a library

The getoptions command is not recommended for use in distribution scripts because it is not always installed on the system. This problem can be solved by including getoptions as a shell script library in your shell scripts.

To use getoptions as a library, you need to generate a library using the gengetoptions command. You can optionally adjust the indentation and other settings when generating the library.

$ gengetoptions library >
. ./ # Or include it here

parser_definition() {
  setup REST help:usage -- "Usage: [options]... [arguments]..."

eval "$(getoptions parser_definition parse)"
parse "$@"
eval "set -- $REST"

NOTE for 1.x and 2.x users: The previous version guided you to use lib/*.sh. This is still available, but it is recommended to use gengetoptions library.

Use as a generator

If you do not want to include getoptions in your shell scripts, you can pre-generate an option parser. It also runs the fastest, so it suitable when you need a lot of options.

$ gengetoptions parser -f examples/ parser_definition parse prog >
. ./ # Or include it here

parse "$@"
eval "set -- $REST"

Embedding into a file

You can use gengetoptions embed to embed the generated code in a file, which makes maintenance easier.

If you want to write the parser definition in the same file as the shell script to execute, define it between @getoptions and @end. The code contained here will be executed during code generation.

The generated code will be embedded between the @gengetoptions and @end directives. The arguments of @gengetoptions are the same as the arguments of the gengetoptions command, which allows you to embed the library as well as the parser.



set -eu

# @getoptions
parser_definition() {
  setup   REST help:usage -- "Usage: [options]... [arguments]..." ''
  msg -- 'Options:'
  flag    FLAG    -f --flag                 -- "takes no arguments"
  param   PARAM   -p --param                -- "takes one argument"
  option  OPTION  -o --option on:"default"  -- "takes one optional argument"
  disp    :usage  -h --help
  disp    VERSION    --version
# @end

# @gengetoptions parser -i parser_definition parse
# @end

parse "$@"
eval "set -- $REST"

printf '%s\n' "$@" # rest arguments
$ gengetoptions embed --overwrite


Ubuntu (dash) Core i7 3.4 Ghz

Benchmark #1: ./ --flag --param param --option=option a b c
  Time (mean ± σ):       8.6 ms ±   0.3 ms    [User: 6.3 ms, System: 0.6 ms]
  Range (min … max):     7.7 ms …  10.1 ms    300 runs

Benchmark #1: ./ --flag --param param --option=option a b c
  Time (mean ± σ):       8.3 ms ±   0.4 ms    [User: 5.2 ms, System: 0.5 ms]
  Range (min … max):     7.4 ms …  10.5 ms    322 runs

Benchmark #1: ./ --flag --param param --option=option a b c
  Time (mean ± σ):       4.7 ms ±   0.3 ms    [User: 1.4 ms, System: 0.1 ms]
  Range (min … max):     4.4 ms …   6.5 ms    510 runs

macOS (bash), Core i5 2.4 GHz

Benchmark #1: ./ --flag --param param --option=option a b c
  Time (mean ± σ):      37.6 ms ±   3.2 ms    [User: 29.2 ms, System: 7.4 ms]
  Range (min … max):    33.4 ms …  47.5 ms    66 runs

Benchmark #1: ./ --flag --param param --option=option a b c
  Time (mean ± σ):      31.0 ms ±   3.7 ms    [User: 26.0 ms, System: 4.4 ms]
  Range (min … max):    26.4 ms …  43.8 ms    77 runs

Benchmark #1: ./ --flag --param param --option=option a b c
  Time (mean ± σ):       5.6 ms ±   2.1 ms    [User: 2.8 ms, System: 2.0 ms]
  Range (min … max):     3.9 ms …  15.1 ms    277 runs

How to see the option parser code

It is important to know what kind of code is being generated when the option parser is not working as expected.

If you want to see the option parser code, rewrite it as follows.

# eval "$(getoptions parser_definition parse) exit 1"

# Preload the getoptions library
# (can be omitted when using getoptions as a library)
eval "$(getoptions -)"

# Output of the option parser
getoptions parser_definition parse

The option parsing code generated by getoptions is very simple.

Example option parser code
parse() {
  while OPTARG= && [ $# -gt 0 ]; do
    case $1 in
      --?*=*) OPTARG=$1; shift
        eval 'set -- "${OPTARG%%\=*}" "${OPTARG#*\=}"' ${1+'"$@"'}
      --no-*|--without-*) unset OPTARG ;;
      -[po]?*) OPTARG=$1; shift
        eval 'set -- "${OPTARG%"${OPTARG#??}"}" "${OPTARG#??}"' ${1+'"$@"'}
      -[fh]?*) OPTARG=$1; shift
        eval 'set -- "${OPTARG%"${OPTARG#??}"}" -"${OPTARG#??}"' ${1+'"$@"'}
        OPTARG= ;;
    case $1 in
        [ "${OPTARG:-}" ] && OPTARG=${OPTARG#*\=} && set "noarg" "$1" && break
        eval '[ ${OPTARG+x} ] &&:' && OPTARG='1' || OPTARG=''
        [ $# -le 1 ] && set "required" "$1" && break
        shift ;;
        set -- "$1" "$@"
        [ ${OPTARG+x} ] && {
          case $1 in --no-*|--without-*) set "noarg" "${1%%\=*}"; break; esac
          [ "${OPTARG:-}" ] && { shift; OPTARG=$2; } || OPTARG='default'
        } || OPTARG=''
        shift ;;
        exit 0 ;;
        echo "${VERSION}"
        exit 0 ;;
        while [ $# -gt 0 ]; do
          REST="${REST} \"\${$(($OPTIND-$#))}\""
        break ;;
      [-]?*) set "unknown" "$1"; break ;;
        REST="${REST} \"\${$(($OPTIND-$#))}\""
  [ $# -eq 0 ] && { OPTIND=1; unset OPTARG; return 0; }
  case $1 in
    unknown) set "Unrecognized option: $2" "$@" ;;
    noarg) set "Does not allow an argument: $2" "$@" ;;
    required) set "Requires an argument: $2" "$@" ;;
    pattern:*) set "Does not match the pattern (${1#*:}): $2" "$@" ;;
    notcmd) set "Not a command: $2" "$@" ;;
    *) set "Validation error ($1): $2" "$@"
  echo "$1" >&2
  exit 1
usage() {
Usage: [options]... [arguments]...

  -f, --flag                  takes no arguments
  -p, --param PARAM           takes one argument
  -o, --option[=OPTION]       takes one optional argument
  -h, --help
# Do not execute

Arguments containing spaces and quotes

The getoptions correctly handles arguments containing spaces and quotes without using arrays, which are not available in POSIX shells.

The magic is in the REST variable in the following code.

$ --flag 1 --param value 2 -- 3

eval "$(getoptions parser_definition parse "$0") exit 1"
parse "$@"
eval "set -- $REST"

echo "$REST" # => "${2}" "${5}" "${7}"
echo "$@" # => 1 2 3

Why reuse OPTARG and OPTIND for different purposes?

This is to avoid using valuable global variables. The POSIX shell does not have local variables. Instead of using long variable names to avoid conflicts, we reuse OPTARG and OPTIND. This code has been tested to work without any problem with all POSIX shells (e.g. ksh88, bash 2.03).

If you use getoptions instead of getopts for option parsing, OPTARG and OPTIND are not needed. In addition, you can also use getopts, since OPTARG and OPTIND will be correctly reset after use.

If you still don't like it, you can use the --optarg and --optind options of gengetoptions to change the variable name. In addition, since the license of getoptions is CC0, you can modify it to use it as you like.

About workarounds

The option parser code contains workarounds for some shell bugs. If you want to know what that code means, please refer to


For more information, see References.

Global functions

When the getoptions is used as an external command, three global functions, getoptions, getoptions_help, and getoptions_abbr, are defined in your shell script.

If you are using it as a library, only getoptions is required. The other functions are needed when the corresponding features are used.

Helper functions

Helper functions are (setup, flag, param, etc) used to define option parsers, and are defined only within the global functions described above.



This is an example of basic usage. It should be enough for your personal script.


Shell scripts distributed as utilities may require advanced features and validation.

Custom error handler

By defining the custom error handler, you can change the standard error messages, respond to additional error messages, and change the exit status.

Custom helper functions

By defining your own helper functions, you can easily define advanced options. For example, getoptions does not have a helper function to assign to the array, but it can be easily implemented by a custom helper function.


Complex programs are often implemented using subcommands. When using subcommands in getoptions, parse the arguments multiple times. (For example, parse up to the subcommand, and then parse after it. This design is useful for splitting shell scripts by each subcommand.


If you define a prehook function in the parser definition, it will be calledbefore helper functions is called. This allows you to process the arguments before calling the helper function.

This feature was originally designed to handle variable names with prefixes without complicating getoptions. Therefore, it may not be very flexible.

NOTE: The prehook function is not called in the help.



Recall that the parser definition function is just a shell script. You can extend the functionality by calling it from your function. For example, you could add a required attribute that means nonsense required options.

Practical example

getoptions was originally developed to improve the maintainability and testability for ShellSpec which has number of options. ShellSpec optparser is another good example of how to use getoptions.

NOTE: 2.x breaking changes

  • Calling getoptions_help is no longer needed (see help attribute)
  • Changed the default attribute of the option helper function to the on attribute
  • Improved the custom error handler and changed the arguments
  • Disable expansion variables in the help display

NOTE: 3.x breaking changes

  • Renamed lin/ to lin/
  • Renamed getoptions-cli to gengetoptions
  • Moved library generation feature of getoptions to gengetoptions
  • Removed scanning mode = and #
  • Changed attribute off to no
  • Changed initial value @off to @no

For developers

How to test getoptions

Tests are executed using shellspec.

# Install shellspec (if not installed)
curl -fsSL | sh

# Run tests

# Run tests with other shell
shellspec --shell bash

NOTE: Currently, only the option parser is being tested, and the CLI utilities is not being tested.



Creative Commons Zero v1.0 Universal

All rights are relinquished and you can used as is or modified in your project. No credit is also required, but I would appreciate it if you could credit me as the original author.