Shebang

A shebang or hashbang is a particular line that often begins scripts. The line begins with the characters #!. This line defines which program should be passed the contents of the file. For example:

#!/bin/sh
echo "Hi there!"

The paths in the shebang line may be different of different machines. The env program exists to solve this problem and make scripts portable. This program looks in the user's $PATH to find the location of an application. The path /user/bin/env is commonly used for this utility.

#!/usr/bin/env sh
echo "Hi there!"

Once a shebang line exists, the chmod command can be used to make a script executable.

chmod +x script.sh
./script.sh

The first line adds (+) the executable (x) permission to the file.