POSIX compliant argument parsing example

parse-args.sh

#!/bin/sh

# Example to parse arguments in a POSIX shell file
# Inspired by: https://stackoverflow.com/questions/2875424/correct-way-to-check-for-a-command-line-flag-in-bash

# error codes
invalid_args=-1

# arg defaults
value=""
operation="get"
simulate=0

# arg parsing
usage() {
    echo "Usage: $0 -k {key} [-v {value}] [-o {get | set | remove}] [-s]"
    echo '-k, --key: The item key'
    echo '-v, --value: The item value. Default is: ""'
    echo '-o, --operation: The operation to execute. Default is: get'
    echo '-s, --simulate: Simulate the operation execution. Default is: false'
    exit $invalid_args
}

enumArg() {
    v=$1
    shift

    while test $# != 0
    do
        if [ "$v" = "$1" ]; then
            return
        fi
        shift
    done

    usage
}

requiredArg() {
    if [ -z "$1" ]; then
        usage
    fi
}

requiredArgValue() {
    if [ -z "$1" ]; then
        echo "A value is required for $2"
        exit $invalid_args
    fi
}

while test $# != 0
do
    case "$1" in
        -k|--key)
            requiredArgValue "$2" '-k or --key'
            key=$2
            shift ;;
        -v|--value)
            requiredArgValue "$2" '-v or --value'
            value=$2
            shift ;;
        -o|--operation)
            requiredArgValue "$2" '-o or --operation'
            enumArg "$2" 'get' 'set' 'delete'
            operation=$2
            shift ;;
        -s|--simulate)
            parseArgSimulate
            simulate=1 ;;
        *)
            usage ;;
    esac
    shift
done

requiredArg "$key"

echo "      key: $key"
echo "    value: $value"
echo "operation: $operation"
echo " simulate: $simulate"