Bash Argument Parser Generator

Generate argument parsing for a bash script with short and long options, values, a usage message, -- handling and errors for unknown flags.

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Input

Generate argument parsing for a bash script

Output

deploy.sh

1,123 characters

#!/usr/bin/env bash
set -euo pipefail

usage() {
  cat <<EOF
Usage: deploy.sh [options] [--] [args...]

Options:
  -e, --env VALUE             Target environment (staging, production)
  -t, --tag VALUE             Image tag to deploy
  -n, --dry-run               Print what would happen
  -v, --verbose               More output
  -h, --help                  Show this help
EOF
}

ENV=""
TAG=""
DRY_RUN=false
VERBOSE=false

while [[ $# -gt 0 ]]; do
  case "$1" in
    -e|--env)
      [[ $# -ge 2 ]] || { echo "error: $1 needs a value" >&2; exit 2; }
      ENV="$2"; shift 2 ;;
    --env=*) ENV="${1#*=}"; shift ;;
    -t|--tag)
      [[ $# -ge 2 ]] || { echo "error: $1 needs a value" >&2; exit 2; }
      TAG="$2"; shift 2 ;;
    --tag=*) TAG="${1#*=}"; shift ;;
    -n|--dry-run) DRY_RUN=true; shift ;;
    -v|--verbose) VERBOSE=true; shift ;;
    -h|--help) usage; exit 0 ;;
    --) shift; break ;;
    -*) echo "error: unknown option $1" >&2; usage >&2; exit 2 ;;
    *) break ;;
  esac
done

[[ -n "$ENV" ]] || { echo "error: --env is required" >&2; usage >&2; exit 2; }

# Remaining positional arguments are in "$@"

A while/case loop rather than getopts, because getopts cannot parse --long options and GNU getopt behaves differently on macOS. It handles --opt value, --opt=value and -- to end options, and exits with 2, the convention for usage errors. set -euo pipefail stops the script at the first failing command, unset variable or failing pipe.

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About this tool

Method, assumptions, practical next steps, and limits.

Why not getopts

The getopts builtin is portable but only parses single-letter options, so --dry-run is out of reach. GNU getopt supports long options, but the version on macOS is the old BSD one with different behaviour. A plain while loop over $@, as generated here, works the same everywhere bash does.

The strict mode line

set -e exits on the first failing command, -u treats unset variables as errors, and -o pipefail makes a pipeline fail when any part fails rather than only the last. Together they turn silent failures into visible ones. The set builtin documentation lists each option.

Frequently asked questions

How do I handle --option=value in bash?

Match --option=* in the case statement and take the value with ${1#*=}, which removes everything up to the first equals sign.

Why exit with status 2 on bad arguments?

By convention status 2 means incorrect usage, distinguishing it from a runtime failure (1). Many standard tools follow it.

Is what I paste sent anywhere?

No. The tool runs entirely in your browser with JavaScript. Nothing you type or paste is sent to our server or stored.

Bash Argument Parser Generator

Generate argument parsing for a bash script

deploy.sh

Why not getopts

The strict mode line

Frequently asked questions

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