Example bash long and short options

#!/usr/bin/env bash

# Initialize all the option variables.
# This ensures we are not contaminated by variables from the environment.
file=
verbose=0

show_help() {
  echo "Hello"
}

while :; do
  case $1 in
  -h | -\? | --help)
    show_help # Display a usage synopsis.
    exit
    ;;
  -f | --file) # Takes an option argument; ensure it has been specified.
    if [ "$2" ]; then
      file=$2
      shift
    else
      die 'ERROR: "--file" requires a non-empty option argument.'
    fi
    ;;
  --file=?*)
    file=${1#*=} # Delete everything up to "=" and assign the remainder.
    ;;
  --file=) # Handle the case of an empty --file=
    die 'ERROR: "--file" requires a non-empty option argument.'
    ;;
  -v | --verbose)
    verbose=$((verbose + 1)) # Each -v adds 1 to verbosity.
    ;;
  --) # End of all options.
    shift
    break
    ;;
  -?*)
    printf 'WARN: Unknown option (ignored): %s\n' "$1" >&2
    ;;
  *) # Default case: No more options, so break out of the loop.
    break ;;
  esac

  shift
done

# if --file was provided, open it for writing, else duplicate stdout
if [ "$file" ]; then
  exec 3>"$file"
else
  exec 3>&1
fi

# Rest of the program here.
# If there are input files (for example) that follow the options, they
# will remain in the "$@" positional parameters.