What is shebang in linux

Everything You Need to Know About Shebang in Linux

Welcome to our blog post about Shebang Linux! As a Linux user, you may have come across the term “shebang” or “hashbang” before. If you’re wondering what exactly shebang is and how it works in Linux, then you’re in the right place.

Shebang, also known as hashbang, is a special sequence of characters that tells the Linux operating system what interpreter to use to run a script. It’s commonly used at the beginning of shell scripts, Python scripts, and other scripting languages. Understanding how shebang works is essential for any Linux user who wants to write and execute their own scripts.

What is the Shebang in Linux?

The shebang (or hashbang) is a combination of characters used in the first line of a script or program file in Unix-based operating systems. It consists of a hash character (#) followed by an exclamation mark (!), and then the path to the interpreter or command that should be used to execute the script.

When you run a script or program on Linux, the system uses the shebang line to determine which interpreter or command to use. For example, a Python script might begin with the shebang:

This tells the system to use the Python 3 interpreter to run the script. If the shebang is not specified, the system will try to execute the script with the default shell interpreter.

Shebang Syntax

The shebang syntax consists of the following elements:

• The hash character ( # ) at the beginning of the line indicates that the line is a comment.
• The exclamation mark ( ! ) indicates that the following path is the interpreter or command to be used to execute the script.
• The path to the interpreter or command is specified after the exclamation mark. This can be a full path or a relative path.

Here is an example of shebang syntax:

In this example, the shebang specifies that the Python 3 interpreter should be used to execute the script.

Shebang Examples

Let’s look at some examples of shebang in action.

#!/usr/bin/env python3 print("Hello, World!")

In this example, the shebang specifies that the Python 3 interpreter should be used to execute the script. When you run this script, you should see the message “ Hello, World! ” printed to the console.

#!/bin/bash echo "This is a Bash script"

In this example, the shebang specifies that the Bash shell should be used to execute the script. When you run this script, you should see the message “ This is a Bash script ” printed to the console.

#!/usr/bin/perl print "Hello, World!\n";

In this example, the shebang specifies that the Perl interpreter should be used to execute the script. When you run this script, you should see the message “ Hello, World! ” printed to the console.

Benefits of Using Shebang Linux

There are several benefits to using shebang Linux in your script files:

1. Portability: By using a shebang line, you can ensure that your script file can be executed on different systems without having to modify the command used to run the script.
2. Convenience: A shebang line allows you to run a script file directly, without having to explicitly specify the interpreter to use.
3. Readability: A shebang line at the top of a script file makes it clear which interpreter is being used to run the script, making the file more readable and easier to understand.

Conclusion

Shebang Linux is a simple and effective way to specify which interpreter should be used to execute a script file. By including a shebang line at the top of a script file, you can ensure that the file can be executed on different systems without having to modify the command used to run the script. Additionally, using a shebang line can make your script files more readable and easier to understand for other developers.

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What is Shebang in Linux Shell Scripting?

The seemingly insignificant #! characters at the beginning of a shell script has a major significance on how your script will be executed.

You’ll often come across shell scripts that start with:

This #! is called shebang or hashbang. The shebang plays an important role in shell scripting, specially while dealing with different types of shell.

In this tutorial, you’ll learn:

What is shebang in shell scripting?

The shebang is the combination of the # (pound key) and ! (exclamation mark). This character combination has a special meaning when it is used in the very first line of the script. It is used to specify the interpreter with which the given script will be run by default.

So, if the first line of a script is:

It means the interpreter should be bash shell. If the first line is:

It means the interpreter to be used is Z shell.

The #! is surely special because # is used for comments in shell scripts but here it has a special meaning.

Why the shebang matters in shell scripting?

Here’s the thing. The shebang followed by the executable of the shell is not mandatory for a script.

If you write a simple script like this:

And give it execute permission and run it with the . operator, it will be run by your login shell.

[email protected]:~$ cat sample echo "Namaste, folks!" [email protected]:~$ chmod u+x sample [email protected]:~$ ./sample Namaste, folks! 

Then why do shell scripts include #!/bin/bash line at the beginning of the script?

Because there are several shells available for Linux and UNIX systems. While these shells have mostly common syntax, they do have different syntax or different way of handling things.

This is why it becomes important to specify the correct shell interpreter in the script, otherwise some scripts may produce different results when run in different shells.

Let me show that to you with a simple example.

Importance of specifying shell interpreter with shebang

I have written a sample shell script with an array of distributions. The script then displays the distro at index 2.

distros=("Ubuntu" "Fedora" "SUSE" "Debian") echo "Distro at index 2 is: $"

I have not added the shebang line to specify any shell interpreter. This means when I execute this script, it will be run by the default shell (bash in my case):

Can you guess the output of the script?

[email protected]:~$ ./arrays.sh Distro at index 2 is: SUSE

It shows SUSE at index 2 because array index start at 0 in Bash and many other programming and scripting languages. BUT that’s not the case in Z shell. In Z shell, array index starts at 1.

I have Z shell installed on my system. I change the script and add the shebang line to specify that the script should be run by Z shell by default.

#!/bin/zsh distros=("Ubuntu" "Fedora" "SUSE" "Debian") echo "Distro at index 2 is: $"

Can you guess the output when I run the script now?

[email protected]:~$ ./arrays.sh Distro at index 2 is: Fedora

Do you notice the difference now? It’s the same script but the addition of the shebang line made the difference.

And this is why specifying the correct shell interpreter with shebang operator is important. As a sysadmin, you might write shell scripts keeping a specific shell in mind, be it bash, ksh or zsh. But you cannot be sure that the system that will run the script will have the same default shell as yours. Now things make sense, right?

Shebang is ignored if you explicitly specify shell

Why am I stressing on «default» shell? Because the shebang specifies the interpreter to run the script with.

You may, however, specify the shell explicitly and in such cases, the shebang line will be ignored.

How exactly the shebang work?

When you use the shebang in the first line of a script, you are telling the shell to run the given script with the specified command.

Basically, #!/bin/zsh is equivalent to:

I have told you that if the first line of a script starts with shebang, it means you are specifying the shell interpreter.

That’s only partially true. Actually, that’s the purpose of the shebang character. But it’s not necessary that shebang line must have executable of a shell. It can be anything.

For example, I am going to replace #!/bin/zsh with #!/bin/cat . /bin/cat is the executable of the cat command.

#!/bin/cat distros=("Ubuntu" "Fedora" "SUSE" "Debian") echo "Distro at index 2 is: $"

This means that now this script will run with cat command and display the content of the script.

It will work as long as it points to an executable command. If you put some random stuff, it will throw error.

I change the shebang line to:

Clearly, it does not point to the executable of any command and thus it throws a bad interpreter error.

[email protected]:~$ cat arrays.sh #!/home/abhishek distros=("Ubuntu" "Fedora" "SUSE" "Debian") echo "Distro at index 2 is: $" [email protected]:~$ ./arrays.sh bash: ./arrays.sh: /home/abhishek: bad interpreter: Permission denied

Conclusion

Let me answer a few more questions before ending this article:

• It is important that there is no space between # and ! . You CANNOT use it like this: # !/bin/bash .
• Most system allow space between #! and /bin/bash however it is a good practice to avoid space between #! and /bin/bash .
• #! has to be on the first line, otherwise the shebang line will be treated as comment. You cannot even have a blank line before it.

I hope you have a better understand on why #! is used in the beginning of shell scripts in Linux. Feel free to leave a comment if you have questions or suggestions.

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What is Shebang and How to Use this Character Sequence in Linux

One of the best features of Linux is that you can easily create scripts that are designed to automate and simplify tasks. This can help when processing large groups of files, like log files if you’re a Systems Administrator or CSV and TXT files if you’re doing some kind of research. However, there’s one very specific set of characters that you have to understand to get scripting – the Shebang or #! . We answer all your questions about the Shebang in this tutorial, a guide on how to use this character set in Linux.

What Is the Shebang?

The Shebang, or #! , is a character set used to direct your system on which interpreter to use. If you’re not familiar with what an interpreter is, it’s basically the program that reads the commands you enter into the terminal on your Linux system. You probably know it as Bash, but you also could use Fsh, Zsh, or Ksh.

This is a binary program that reads the commands you put into it, like ls or xargs , and figures out what to do with them. The full path is usually /bin/bash or something like that. Check out our guide on the Linux virtual directory structure if you’re confused what that means.

#! is used in a text file of some kind to load the proper interpreter for the code that’s below that file. You could write out a script like what is shown in the following image.

And run it like what is shown in this image.

That will work for you, but it may get annoying after a while. A better way to do it might be like this image.

And then run it like this.

Why Was the Shebang Invented?

While using the Shebang takes an extra step when creating the script, being able to use a ./ or “dot-slash” to run your scripts will make it easier down the road. The script takes care of which interpreter to pass the commands to, meaning you don’t have to remember. This is great if you’re scheduling it as a cron job or if you’re executing scripts from within other scripts.

It makes the system more simple to administer because regardless of whether you want Bash, Zsh, or Python to interpret the contents of the files, having that as the first line of your script will make it drop-dead simple.

How Do I Use the Shebang?

It’s very simple: just type it in the first line of your script file along with the absolute path to the interpreter you want to pass the commands to. Here’s a couple of examples:

#!/bin/bash #!/bin/zsh #!/usr/bin/env python3

Once that’s in the file, start typing below it. Once you’re done, save your file and make it executable by running one of the following commands:

chmod 755 SCRIPT-NAME chmod a+x SCRIPT-NAME

They will both accomplish the same thing. From there, all you have to do is run your script like this:

And you’re done! It’s that simple.

If you enjoyed this guide on how to use the Shebang, make sure you check out some of our other Linux how-to’s, like our guides on fixing the “No space left on device” error and repairing a corrupted USB drive.

John is a young technical professional with a passion for educating users on the best ways to use their technology. He holds technical certifications covering topics ranging from computer hardware to cybersecurity to Linux system administration.

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