Shebang Bash Explained with Examples

Bash is a command language interpreter. Many operating systems incorporate bash as the default command interpreter, especially most of the GNU/Linux systems. Bash scripting is a method of automating a set of commands that would otherwise be executed interactively one-by-one.

In this guide, check out what shebang bash is and how to use it.

Shebang Bash:

In bash scripting, Shebang is a way to declare what interpreter the operating system will use to parse the rest of the file. The Shebang is characterized by the set of characters “#!” (without quotes).

Here's a quick breakdown of the Shebang interpreter directive.

#! [arguments]

For example, if a script is to be parsed using the Bash shell, then the Shebang interpreter directive would look like this.

#!/bin/bash

The Shebang interpreter directive has certain properties.

It must be the first line of the script.
It must start with a shebang (#!).
There may or may not be whitespace after the shebang (#!).
The interpreter will be the full path to a binary file.
There may or may not be interpreter arguments.

Here's a shortlist of some of the most common Shebang interpreter directives.

#!/bin/bash: The script will be parsed using bash.
#!/usr/bin/python: The script will be parsed using the python binary.
#!/usr/bin/env perl: The script will be parsed using the perl executable. The location of the perl executable will be provided by the env command.

Using Shebang Bash:

Scripts can have no Shebang bash. Any such script will be parsed using the default interpreter. For example, bash is the default interpreter for bash and sh for zsh. While most of the UNIX/Linux systems have bash as the default, users have options to use others. In such a scenario, without declaring the interpreter, the script may not perform its preferred task.

There are two methods of using the Shebang directive to declare the interpreter. The first one is to declare the file path to the executable.

#!/bin/bash

Another method is to use the env utility to locate the executable.

#!/usr/bin/env bash

The benefit of using the env utility is, it will look for the executable under the $PATH environment variable of the current user. In this example, env will look for the bash. If there is more than one bash executable declared in the $PATH variable, then the first one will be used.

As mentioned, Shebang bash also supports executable arguments. For example, to use bash with debug mode, the Shebang interpreter directive would look like this.

#!/bin/bash -x

When it comes to using env for the Shebang bash, adding an executable argument requires using the “set” option. For example, the following one will use bash with debug mode enabled.

#!/usr/bin/env bash
$ set -x

Script Example:

We've discussed the basics of Shebang bash. It's time to put it into practice. Let's have a look at the implementation of Shebang bash.

Launch the text editor of your choice and type the following script:

$ #!/bin/sh
$ echo "hello_world_bash"

Save the file. To run the script, it has to be marked as an executable. Run the following command:

$ chmod +x