Argument Parsing in Bash

argParse.sh

#!/usr/bin/env sh

# Variable for the script description
_ARGPARSE_SCRIPT_DESCRIPTION=""

# Use this one wierd trick to shorten your CLI Boolean Flags
_ARGPARSE_FLAG_BEHAVIOUR="Add this flag to set the argument to 'true' (don't use '--flag true')"

# Declare an associative array for argument properties
_ARGPARSE_ARG_VALUES=()

# Default Enums and Values
_ARGPARSE_NULL_VALUE_="null"
_ARGPARSE_DEFAULT_=1
_ARGPARSE_HELP_=2
_ARGPARSE_TYPE_=3
_ARGPARSE_OPTIONAL_=4
_ARGPARSE_NUM_VALUES_=5 # Total number of properties per argument

# Debug printing helpers
if [ -t 1 ]; then
    _COLOR_ERR_SET="$(tput setaf 1)"
    _COLOR_SET="$(tput setaf 4)"
    _COLOR_RESET="$(tput sgr0)"
else
    _COLOR_ERR_SET=${_COLOR_ERR_SET:-}
    _COLOR_SET=${_COLOR_SET:-}
    _COLOR_RESET=${_COLOR_RESET:-}
fi

# Function to set the script description
# Usage: setDescription "Description text"
setDescription() {
    _ARGPARSE_SCRIPT_DESCRIPTION="$1"
}

# Function to display help
# Usage: showHelp
showHelp() {
    local args=( "${_ARGPARSE_ARG_VALUES[@]}" )
    local prefix="   "

    echo "\nUsage: $0 [arguments...]"
    echo ""
    echo "$_ARGPARSE_SCRIPT_DESCRIPTION"
    echo ""
    echo "Arguments:"
    for ((i=0; i<${#args[@]}; i+=$_ARGPARSE_NUM_VALUES_)); do
        [[ ${args[i+_ARGPARSE_DEFAULT_]} == "$_ARGPARSE_NULL_VALUE_" ]] &&  args[i+_ARGPARSE_DEFAULT_]=''
        if [[ ${args[i+_ARGPARSE_TYPE_]} == "bool" ]]; then
            args[i+_ARGPARSE_TYPE_]=''
            args[i+_ARGPARSE_HELP_]="${args[i+_ARGPARSE_HELP_]} $_ARGPARSE_FLAG_BEHAVIOUR"
        else
            args[i+_ARGPARSE_TYPE_]="<${args[i+_ARGPARSE_TYPE_]}>"
        fi
        printf "%s ${_COLOR_SET}%-20s${_COLOR_RESET}: (%8s) %s\n" "$prefix" "--${args[i]} ${args[i+_ARGPARSE_TYPE_]}" "${args[i+_ARGPARSE_OPTIONAL_]}" "${args[i+_ARGPARSE_HELP_]} (defaults to '${args[i+_ARGPARSE_DEFAULT_]}')"
    done
    printf "%s ${_COLOR_SET}%-20s${_COLOR_RESET}: Display this help\n"  "$prefix" "-h | --help"
}

# Function Alias to display help
# Usage: usage
usage()
{
  showHelp
}

# Internal Helper Function to check an Argument
# Usage: _checkRequired "$@"
_checkRequired() {
    for ((i=0; i<${#_ARGPARSE_ARG_VALUES[@]}; i+=$_ARGPARSE_NUM_VALUES_)); do
        if [[ "${_ARGPARSE_ARG_VALUES[i+_ARGPARSE_OPTIONAL_]}" == "required" ]]; then
            if ! (echo "$@" | grep "${_ARGPARSE_ARG_VALUES[i]}") >/dev/null ; then
                echo "${_COLOR_ERR_SET}Error${_COLOR_RESET}: '--${_ARGPARSE_ARG_VALUES[i]}' is required" >&2
                showHelp >&2
                exit 1
            fi
        fi
    done
}

# Function to define a command-line argument
# Usage: defineArgument "argumentName" ["default"] ["help text"] ["type"] ["required"]
defineArgument() {
    argumentName=$1
    argumentValue=${2:-"$_ARGPARSE_NULL_VALUE_"}
    argumentHelp=${3:-""}
    argumentType=${4:-"string"}
    argumentIsOptional=${5:-"optional"}
    if [[ "$argumentIsOptional" == "required" ]]; then
        argumentValue="$_ARGPARSE_NULL_VALUE_"
    fi
    _ARGPARSE_ARG_VALUES+=("$argumentName" "$argumentValue" "$argumentHelp" "$argumentType" "$argumentIsOptional")
    if [[ "$argumentValue" == "$_ARGPARSE_NULL_VALUE_" ]]; then
        argumentValue=""
    fi
    export "$argumentName"="$argumentValue"
}

# Function to parse command-line arguments
# Usage: parseArgs "$@"
parseArgs() {
    # Set Description
    _setDefaultDescription
    # Check for help
    _checkForHelp "$@"
    # Check for missing required arguments
    _checkRequired "$@"
    while [[ $# -gt 0 ]]; do
        key="${1#--}" # remove '--' prefix
        if ! (echo "${_ARGPARSE_ARG_VALUES[*]}" | tr " " "," | grep "$key," > /dev/null ); then
            echo "${_COLOR_ERR_SET}Error${_COLOR_RESET}: Unknown argument '$key'" >&2
            showHelp >&2
            exit 1
        fi
        for ((i=0; i<${#_ARGPARSE_ARG_VALUES[*]}; i+=5)); do
            if [[ "$key" == "${_ARGPARSE_ARG_VALUES[i]}" ]]; then
                case ${_ARGPARSE_ARG_VALUES[i+_ARGPARSE_TYPE_]} in
                'string')
                    if [[ -z "${2:-}" || "${2:-}" == --* ]]; then
                        echo "${_COLOR_ERR_SET}Error${_COLOR_RESET}: Missing value for argument --$key" >&2
                        exit 1
                    else
                        export "$key"="$2"
                        shift 2
                    fi
                ;;
                'bool')
                    if [[ -z "${2:-}" || "${2:-}" == --* ]]; then
                        export "$key"='true'
                        shift
                    else
                        echo "${_COLOR_ERR_SET}Error${_COLOR_RESET}: Extra value for argument --$key" >&2
                        exit 1
                    fi
                ;;
                *)
                    echo "${_COLOR_ERR_SET}Error${_COLOR_RESET}: Unknown argument type '${_ARGPARSE_ARG_VALUES[i+_ARGPARSE_TYPE_]}' for '$key'" >&2
                    exit 1
                ;;
                esac
            fi
        done
    done
}

# Internal Function to check for help option
# Usage: _checkForHelp "$@"
_checkForHelp() {
    if (echo "$@" | grep -- "-h" > /dev/null) || (echo "$@" | grep -- "--help" > /dev/null); then
        showHelp
        exit 0
    fi
}

# Function to set the default script description
# Usage: _setDefaultDescription
_setDefaultDescription() {
    _ARGPARSE_SCRIPT_DESCRIPTION=${_ARGPARSE_SCRIPT_DESCRIPTION:-"Description not given."}
}

# Internal Main Function
# Usage: main "$@"
main() {
  setDescription "This is an argument parser, adapted from https://github.com/yaacov/argparse-sh/"
  defineArgument "debug" "false" "Enable debug mode" "bool" "optional"
  parseArgs "$@"
  if [[ $debug == "true" ]]; then
    echo "Debug mode is ON."
  fi
  exit 0
}

# Standalone Invocation
if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
  main "$@"
fi

This is adopted from: /yaacov/argparse-sh. It fixes a few known bugs, when the argument is missing or when an extra value it set erroneously.