Shebang

External

• https://en.wikipedia.org/wiki/Shebang_(Unix)#:~:text=In%20computing%2C%20a%20shebang%20is,bang%2C%20or%20hash%2Dpling.
• https://tldp.org/LDP/abs/html/sha-bang.html

Internal

• bash
• env

Overview

The #! sequence of characters at the beginning of a file indicates that the file is a script: a set of commands to be fed into an interpreter. The #! is actually a two-byte magic number, a special marker that designates a file type, or in this case an executable script. The path that follows #! is the path to the program that interprets the commands in the script, whether it be a shell, a programming language, or a utility. The interpreter executes the commands in the script, starting with the line following the #! line:

#! <interpreter> [optional-args]

The Path Must be Absolute

The interpreter should always be specified by absolute path to ensure that the script can be executed from any directory. When it's not, it's generally a typo and shell static checkers usually warn against this syntax.

Bash

#!/usr/bin/env bash
echo "."

Python

#!/usr/bin/env python
print('.')