#!

A hash-bang, usually written ‘#!’, is the traditional beginning of shell scripts on Unix based platforms.

The text following these two characters denotes the interpreter that the script should be executed though.

Thus:

#!/bin/bash
... Some scripting here ...

indicates that the script should be run under Bash. Likewise ‘/usr/share/php’ for PHP, ‘/usr/share/python’ for Python and so on.

The author of this blog acknowledges that the two characters are also known as a SheBang but thinks that this term sounds like a lyric from a Ricky Martin song. We will have none of that evil here.