Shebang line (#!/bin/bash) in Bash Scripting

Introduction

The shebang line tells the computer which program to use to run your script. It helps your script run correctly without extra typing.

When you write a bash script and want to run it directly from the command line.

When you want to make your script portable and clear about which shell to use.

When you share your script with others so it runs the same way on their computers.

When automating tasks that require bash features specifically.

When running scripts on systems with multiple shells installed.

Syntax

Bash Scripting

#!/bin/bash

This line must be the very first line in your script.

It starts with #! followed by the path to the bash program.

Examples

This script uses the shebang to run with bash and prints a greeting.

Bash Scripting

#!/bin/bash

echo "Hello, world!"

This uses /usr/bin/env to find bash in the system's PATH, making it more portable.

Bash Scripting

#!/usr/bin/env bash

echo "Using env to find bash"

Sample Program

This script starts with the shebang line to specify bash. It then prints a welcome message.

Bash Scripting

#!/bin/bash

# This script prints a welcome message

echo "Welcome to bash scripting!"

Important Notes

Make sure your script file has execute permission (e.g., chmod +x script.sh).

If the shebang line is missing, you must run the script by explicitly calling bash (bash script.sh).

Summary

The shebang line tells the system which shell to use to run your script.

It must be the first line in your script and starts with #!.

Using the shebang makes running scripts easier and more consistent.