An empty Bash script as a template. See #TODO for places to change.

template.inc.sh

#!/bin/bash
usage() { sed 's/^    //' >&2 <<<USAGETEXT
    #TODO: Description of script here.

    Usage:
$(sed -r 's/^#@@ (.*)$/    \1/p' < "${BASH_SOURCE[0]}")

    Variables:
$(sed -r 's/^#@# (.*)$/    \1/p' < "${BASH_SOURCE[0]}")
USAGETEXT
    exit 1
}

set -euo pipefail; IFS=$'\n\t'
if command -v shellcheck &>/dev/null; then shellcheck "$0"; fi

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
BASENAME="$(basename "${BASH_SOURCE[0]}")"
shopt -s expand_aliases

source "${dir}/xplatform.inc.sh"
log() { echo "$(date +%T) $1: $2" >&2; }
info() { log "INFO" "$1"; }
warn() { log "WARN" "$1"; }
# Run command while echoing what it's doing
x() { (set -x -euo pipefail; "$@";); }
die() { log "ERROR" "$1"; exit 1; }
# Like xargs but works for a function.
fargs() { "$@" $(</dev/stdin); }
# Load configuration
config() { if [[ -f "$1" ]]; then source "$1"; fi; }
config "$DIR/${BASENAME}.conf"
config "$HOME/.config/${BASENAME}"
config "$PWD/.${BASENAME}"

# Sub-Commands go here.  Pattern: $basename-subcommand() {}
# Lines that start with #@@ are available in usage.

#TODO: remove xxx-subcommand, VAR1 examples

#@# VAR1
#@#     A configuration variable for some use.
VAR1="${VAR1:-defaultvalue}"

#@@ subcommand
#@@     Does something.
xxx-subcommand() {
    set -euo pipefail
    # Code goes here
}

main() {
    [[ "$#" -gt 0 ]] || usage

    case "$1"; do
        help|usage)
            usage 2>&1 || true; exit 0
            ;;
        repl)
            echo 'Type jf-help for help'
            while read -e -i "$*" -p "$0 \$ " line; do $line; done
            ;;
        *)
            command="${BASENAME}-$1"; shift
            command -v "$command" 2>/dev/null || die "Unknown command: ${command}"
            "$command" "$@"
            ;;
    done        
}

# This is the main entrypoint.  This should stay at end of this file.
main "$@"

TODO:

• Include default args from: ${HOME}/.config/${basename}:${HOME}/.${basename},${PWD}/.${basename}
• Make a general-purpose library and source include it. It will include xplatform.
• option: -c/--config - Read config from alternative file. default args in ini format. Sections=subcommands.
• option: -e/--env <var>=<value> - set environmental variable
• option: -C <path> - work dir. cd before running command.
• option: -p/--paginate - send output to less
• options: -g/--grep - filter output with a regex
• option: --no-ansi - sed to strip colors
• option: -q/--quiet - no stderr messages.
• option: --version - calls version subcommand
• option: -y/--yes - Use default answers for any questions.
• options: --version, --help - calls command of same name
• command: repl - interactive command line to run commands. No prompt if not a tty.
• commands: help, version, env (show variables)
• For usage, if command not in source, search path:
  tr ':\n' '\0\0' <<<"$PATH" | xargs -0 -I{} find '{}' -maxdepth 1 -maxdepth 1 -name "$comand"