Skip to main content

Understanding the Shebang (#!) in the Terminal

A shebang (written as #!) is a character sequence at the very first line of a script in Unix-like operating systems (such as Linux and macOS). It tells the operating system's kernel which program (interpreter) to use to execute the code in that file.

Why Is It Important?​

When you try to execute a text file directly, the operating system needs to know if it is reading a Bash script, a Python file, or something else.

  • Removes Guesswork: The system immediately knows the correct interpreter.
  • Ensures Portability: Your script runs exactly as intended, regardless of the user's default terminal shell.

Common Examples​

Bash​

#!/bin/bash

or (more portable):

#!/usr/bin/env bash

Python​

#!/usr/bin/python3

or (more portable):

#!/usr/bin/env python3
tip

Using the #!/usr/bin/env path is highly recommended. Instead of hardcoding a specific location for an interpreter, it tells the system to search your environment's $PATH variable to find the program.

Crucial Rules​

  1. First Line: It must be on the very first line of the script.
  2. No Spaces: There cannot be any spaces before the #!.
  3. Correct Path: It must point to a valid executable path on your system.

Step-by-Step Implementation​

To run a script directly by its name in the terminal, you must include a shebang and grant the file execution permissions.

1. Create the Script​

Create a file named hello.sh and add the shebang at the top:

#!/bin/bash
echo "Hello, World!"

2. Make the Script Executable​

In your terminal, use the change mode command to grant execution permissions:

chmod +x hello.sh

3. Run Your Script​

Execute the file directly from your terminal:

./hello.sh