Glossary

Shebang (#!)

The first line telling the system which interpreter runs a script.

A shebang is the two characters #! at the very start of a script, followed by the interpreter's path: #!/bin/bash, #!/usr/bin/env python3. When you execute the file, the kernel reads that line and launches the named interpreter with your script as its argument.

It must be line 1, column 1. Combined with the execute permission (chmod +x), it is what turns a text file into something you can run directly as ./script.sh.

See it in practice

$ head -n 1 /usr/bin/*.sh 2>/dev/null | head

Peek at the first line of installed scripts and you will see the shebangs that make them runnable.

Where you'll meet it