How I start all my shell scripts

boilerplate.sh

#!/usr/bin/env bash
# 
# Short header explaining what the script does
#

# exit on error, error on unbound variables, disable glob expansion, fail within pipes
set -eufo pipefail
[[ -n "${DEBUG:-}" ]] && set -x

: "${VAR_A=default_value_a}"
: "${VAR_B=default_value_b}"

log() {
  # Pro Tip: declare local before assignment (http://tldp.org/LDP/abs/html/localvar.html)
  local level
  local message

  level="$(echo $1 | tr '[:lower:]' '[:upper:]')" ; shift
  message=("$@")

  # disable colorized output unless it's to a terminal
  if [[ -t 1 ]]; then
    local color
    local reset
    reset=$(echo -ne "\033[0m")

    case $level in
      ERR*)  color=$(echo -ne "\033[91m") ;; # light red
      WARN*) color=$(echo -ne "\033[93m") ;; # light yellow
      OK*)   color=$(echo -ne "\033[94m") ;; # light blue
      INFO*) color=$(echo -ne "\033[97m") ;; # white
      TASK*) color=$(echo -ne "\033[96m") ;; # light cyan
      *)     color=$(echo -ne "\033[39m") ;; # default
    esac

    echo "${color}[${level}]${reset} ${message}"
  else
    echo "[${level}] ${message}"
  fi
}

main() {
  log info "${FUNCNAME[0]} $@"
  # Handle command line args and shift them out of $@ after use
  while getopts 'a:b:' flag; do
    case "${flag}" in
      a) VAR_A="${OPTARG}" ;;
      b) VAR_B="${OPTARG}"  ;;
    esac
  done
  shift $(($OPTIND - 1))
  
  # Print usage
  if [[ -z "$@" ]]; then
    echo "Usage: $0 [-a <VAR_A>] [-b <VAR_B>] <arg> [<arg> ...]"
    exit 1
  fi
}

main "$@"