The first two statements of your BASH script should be…

script.sh

#!/usr/bin/env bash
set -euo pipefail

The first statement is a Mac, GNU/Linux, and BSD portable way of finding the location of the bash interpreter.

The second statement combines:

• set -e which ensures that your script stops on first command failure. By default, when a command fails, BASH executes the next command. Looking at the logs, you might feel that the script executed successfully while some commands might have failed. Caveat: Be careful about applying it to existing scripts.
• set -u which ensures that your script exits on the first unset variable encountered. Otherwise, bash replaces the unset variables with empty default values.
• set -o pipefail which ensures that if any command in a set of piped commands failed, the overall exit status is the status of the failed command. Otherwise, the exit status is the status of the last command.

#!/bin/sh 
# Author:
# License: Unlicense

set -euf

log() {
    printf '\033[32m->\033[m %s\n' "$*"
}

die() {
    log "$*" >&2
    exit 1
}

usage() {
    echo "${0##*/} ARGS
    desc
    "
    exit 0
}

Valid template for shell scripts.