A simple template for bash scripts

bash-template.sh

#!/usr/bin/env bash

# Inspired from: https://gist.github.com/b1zzu/ccd9ef553d546a2009eca21ab45db97a

set -eEu -o pipefail
# shellcheck disable=SC2154
trap 's=$?; echo "$0: error on $0:$LINENO"; exit $s' ERR

SCRIPT=$0

# Defaults
# ---

DEFAULT_GLOBAL='some_default_value'
DEFAULT_DEMO_NAME='default value for the demo name option'

# Variables
# ---

GLOBAL=${GLOVAL:-${DEFAULT_GLOBAL}}
DEMO_NAME=${DEMO_NAME:-${DEFAULT_DEMO_NAME}}

# Help
# ---

function usage() {
    echo
    echo "Usage: ${SCRIPT} [OPTIONS] COMMAND"
    echo
    echo "Options:"
    echo "  --global string     some global flag (default: ${DEFAULT_GLOBAL}) (env: GLOBAL)"
    echo
    echo "Commands:"
    echo "  demo                        print a demo message"
}

function demo_usage() {
    echo
    echo "Usage: ${SCRIPT} [GLOBAL_OPTIONS] demo [OPTIONS] MESSAGE"
    echo
    echo "Options:"
    echo "  --name string     some name for the demo cmd (default: ${DEFAULT_DEMO_NAME}) (env: DEMO_NAME)"
}

# Utils
# ---

function fatal() {
    echo "$SCRIPT: error: $1" >&2
    return 1
}

function info() {
    echo "$SCRIPT: info: $1" >&2
}

# Commands
# ---

function demo_command() {

    # Positional Arguments
    MESSAGE=

    # Parse Command Arguments
    while [[ $# -gt 0 ]]; do
        case "$1" in
        -h | --help)
            demo_usage
            return 0
            ;;
        --name)
            DEMO_NAME="$2"
            shift
            shift
            ;;
        --* | -*)
            demo_usage
            echo
            fatal "unknown option '$1'"
            ;;
        *)
            MESSAGE="$1"
            break
            ;;
        esac
    done

    # Command

    if [[ -z "${MESSAGE}" ]]; then
        fatal "MESSAGE is required"
    fi

    info "execute the demo command"

    echo "Demo invoked with:"
    echo "  GLOBAL: '${GLOBAL}'"
    echo "  DEMO_NAME: '${DEMO_NAME}'"
    echo "  MESSAGE: '${MESSAGE}'"

    return 0
}


# Parse arguments
# ---
while [[ $# -gt 0 ]]; do
    case "$1" in
    -h | --help)
        usage
        exit 0
        ;;
    --global)
        GLOBAL="$2"
        shift
        shift
        ;;
    demo)
        shift
        demo_command "$@"
        exit 0
        ;;
    --* | -*)
        usage
        echo
        fatal "unknown option '$1'"
        ;;
    *)
        usage
        echo
        fatal "unknown command '$1'"
        ;;
    esac
done

usage
echo
fatal "command not specified"