hello

#! /usr/bin/env bash
#
# I'm a template for a clean and modern bash program.
# I also serve as a demo of essential bash features and good practices.
# Replace this notice with your own description.
#
# Requires bash >= 4.3.
#
set -eu -o pipefail

usage() {
  cat <<EOF
Usage: $(basename "$0") [OPTIONS]
Print a greeting message.

Options:
  --greeting MSG
      Use another greeting message than '$default_greeting'.
  --help
      Print this error message and exit.
EOF
}

default_greeting="Hello"

greeting="$default_greeting"
while [[ $# -gt 0 ]]; do
  case "$1" in
    --greeting)
      greeting="$2"
      shift
      ;;
    --help)
      usage
      exit 0
      ;;
    *)
      echo "Unsupported argument '$1'. Try --help." >&2
      exit 1
  esac
  shift
done

set_username() {
  username="stranger"
  if [[ -v USER ]]; then
    username="$USER"
  fi
}

set_username
echo "$greeting, $username."