The Shebang (#!)

#!/bin/bash

This is the first line of the script above. The hash exclamation mark ( #! ) character sequence is referred to as the Shebang. Following it is the path to the interpreter (or program) that should be used to run (or interpret) the rest of the lines in the text file. (For Bash scripts it will be the path to Bash, but there are many other types of scripts and they each have their own interpreter.)

Formatting is important here. The shebang must be on the very first line of the file (line 2 won’t do, even if the first line is blank). There must also be no spaces before the # or between the ! and the path to the interpreter.

Whilst you could use a relative path for the interpreter, most of the time you are going to want to use an absolute path. You will probably be running the script from a variety of locations so absolute is the safest (and often shorter than a relative path too in this particular case).

It is possible to leave out the line with the shebang and still run the script but it is unwise. If you are at a terminal and running the Bash shell and you execute a script without a shebang then Bash will assume it is a Bash script. So this will only work assuming the user running the script is running it in a Bash shell and there are a variety of reasons why this may not be the case, which is dangerous.

You can also run Bash, passing the script as an argument.