Choose a shell or programming language in the first line of an executable script.

Absolute

For Bash:

#!/bin/bash

Options

Use options. e.g.

#!/bin/bash -e

Env

This below is the most portable across machines and systems and so is often used for a shebang in a file.

Note the space, since env is a command and bash is the argument. Note options cannot be used in the first line in this format, so you must use set.

#!/usr/bin/env bash
set -e

This is commonly used for other programming languages. e.g.

#!/usr/bin/env python

#!/usr/bin/env node

#!/usr/bin/env ruby

Note that this always starts with #! regardless of what language you are using, since the shell must evaluate the shebang first and then comments of the file in the appropriate language.

Basic

This is valid, but it is not robust, so you should avoid this.

!#bash

!#python