In bash scripting, we often see the sequence of characters #! appear at the beginning of the line. This sequence of characters is called shebang.

shebang is used to proclaim the interpreter that the operating system must use to compile the syntax of the command in the file.

Here at Ibmi Media, as part of our Server Management Services, we regularly help our Customers to perform related Linux system bash queries.

In this context, we shall look into how to use bash shebang in Linux.

What is the syntax of shebang ?

The syntax of shebang is shown below:

#!interpreter [arguments]

interpreter maybe /bin/sh, /bin/bash.

In this command, [arguments] is optional.

How to use shebang in bash scripts ?

If the shebang is not specified with any arguments, the script will be compiled by the default random interpreter used by that shell. In order for your script to be properly interpreted with bash, you need to add the path for the shebang to execute the script.

There are two ways to use shebang as an interpreter. The first way is to proclaim the file path to the executable:

#!/bin/bash

The second way is by using the env utility:

#!/usr/bin/env bash

The advantage of the second way is, it will look for the executable in the $PATH environment variable.

With debug mode:

With bash: you need to add -x after the shebang line:

#!/bin/bash -x

With the env utility, you need to add set -x:

#!/usr/bin/env bash

set -x

Example of shebang

Firstly, let's create a file named "hello" by your text editor:

$ nano hello

Then type the following command:

#!/bin/bash
echo "Hello World"

Save the file.

Before running the script, let’s add execute permission to file by the chmod command:

$ chmod +x hello

Now you can try running the script by typing ./

$ ./hello

The Output will be:

Hello World

How to override the shebang bash ?

If you want to override the interpreter while the shebang bash defined the interpreter to use, let's follow the syntax:

$ <interpreter> <script>

For example, the hello file above is being interpreted with bash. Now we want it follows the sh interpreter:

$ sh hello

Output will be:

Hello World

*Note: You shouldn't override the shebang bash because it will adversely affect the progress of the script.

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