#!/bin/sh set -eu usage() { cat <<-'EOF' Usage: timestamp [-E] EOF } EXTENDED=false while getopts 'E' flag; do case "$flag" in (E) EXTENDED=true ;; (*) usage >&2 exit 2 ;; esac done shift $((OPTIND - 1)) if [ "$EXTENDED" = true ]; then date '+%Y-%m-%dT%H:%M:%S%:z' else date '+%Y-%m-%d' fi