example.bash

#!/usr/bin/env bash

#===============================================================================

args=()
opts=( 'a' 'b' 'c' )
verbose='no'
version='1.0'

a='no'
b='no'
c=''

#===============================================================================

main() {
  show_input
  so 'This message is sent to stdout'
  se 'This message is sent to stderr'
  ok 'This is a success message'
  wrn 'This is a warning message'
  err 'This is an error message'
  dbg 'This is a debug message'
}

#===============================================================================

show_input() {
  local 'arg' 'opt'
  if (( "${#opts[@]}" > 0 )); then
    dbg 'Options:'
    for opt in "${opts[@]}"; do
      dbg "  ${opt}: [${!opt}]"
    done
  fi
  if (( "${#args[@]}" > 0 )); then
    dbg 'Arguments:'
    for (( arg = 1; arg <= "${#args[@]}"; arg++ )); do
      dbg "  ${arg}: [${args[arg-1]}]"
    done
  fi
}

#-------------------------------------------------------------------------------

so() { printf '%s\n' "${@}"; }
se() { printf '%s\n' "${@}" >&2; }
ok() { printf '\e[1;32m[OK]\e[0m %s\n' "${@}" >&2; }
wrn() { printf '\e[1;33m[WARNING]\e[0m %s\n' "${@}" >&2; }
err() { printf '\e[1;31m[ERROR]\e[0m %s\n' "${@}" >&2; }
dbg() { if [[ "${verbose}" == 'yes' ]]; then dbg() { printf \
'\e[1;34m[DEBUG]\e[0m %s\n' "${@}" >&2; }; dbg "${@}"; else dbg() { :; }; fi; }

#-------------------------------------------------------------------------------

show_help() {
cat << 'EOF'
Usage: script [--help|--version] [--verbose] [-a] [-b] [-c] [--] [operands]
EOF
}

#===============================================================================

while [[ "${1++}" ]]; do
  case "${1}" in
    ( '-a' )
      a='yes'
      ;;
    ( '-b' )
      b='yes'
      ;;
    ( '-c' )
      c="${2}"
      shift
      ;;
    ( '--help' | '-h' )
      show_help
      exit
      ;;
    ( '--verbose' | '-v' )
      verbose='yes'
      ;;
    ( '--version' | '-V' )
      so "${version}"
      exit
      ;;
    ( '--' )
      shift
      args+=( "${@}" )
      break
      ;;
    ( * )
      args+=( "${1}" )
      ;;
  esac
  shift || break
done

main