What is bash file in linux

What is Bash in Linux? [Running, Finding & Making]

Creating own script according to personal demand is the most fascinating thing a programmer wishes for. Bash gives us just that perfect option to create our own scripts in Linux. In this article, you will get to know what is bash in Linux and other interesting options of bash which will make you a pro user.

What is Bash in Linux?

1. Bash as a Shell

Bash(Bourne Again Shell) is the most popular command language interpreter for the GNU operating system. It supports functions, variables, flow controls and also reads and executes commands from a file. It works as the middleman or shell between the computer and the human command line.

2. Bash as a command

Inside the bash shell, there is a bash command also. This command is used to run files or text windows.

1. Bash as a Command

1.1 Synopsis of Bash

On the man page of bash, you can find all the descriptions and uses of the bash command. It takes all the single-character shell options and a number of multi-character options. Bash pipes the command strings in a specified file.

2. Bash as a Shell

2.1 How to Run a Bash in Linux

Whenever you are using a terminal in our Linux operating system, you are using the bash every time. To run a bash shell in your machine you can follow some steps given below: Steps to Follow: ➊ At first open the Ubuntu Terminal by pressing CTRL + ALT + T. ➋Type the following command in the command prompt:

➌Press the ENTER button. Output: After that, you will be able to see that you are running bash as your shell or interpreter. Note: If you don’t see this, it means you are running other shells. You can download and install bash if you want to use it.

2.2 Finding Bash in Linux

You need to know where the bash interpreter is located on your machine. To learn about it you should follow the steps given below: Steps to Follow: ➊ Open the terminal first. ➋ Type the following command in the command prompt:

➌Press the ENTER button. Output: After that, you will be able to see the location of your bash interpreter. As you can see here, my bash shell is located in the /usr/bin/bash directory.

2.3 How to Make a Bash File in Linux

To make a bash file you should follow some procedures. Those are given below: Steps to Follow: ➊ Open the terminal first. ➋ You can choose any text editor to open a file. Here I have used the nano text editor to open a bash file. I have given the following command in the command prompt:

➌ After opening the nano file you have to give the following command first. This is a must to begin any bash file.

Though other lines starting with a # sign do not have any particular meaning. They are just taken as a comment by the machine. Only this line starting with a #! (shebang) sign in the bash file has a particular meaning. So the second line in this file is just a comment, you don’t have to write it. ➍ Next, I have put three values. Those are:

echo “Hello, how are you? $USER” echo “Today is $(date)” echo “Have a good day”

I want to execute these three values. Here $USER gives us the user name of the machine. $(date) will show the date and time of the machine. ➎ Finally you just save the file using CTRL+S and exit the file press CTRL+X. Output: Now you come back to your command prompt. To run the bash file you have to type this command:

You can see in the picture that three echo commands are executed correctly and got the desired values by just running the file. Where borhan is the user of the machine and Mon Nov 28 4:421:38 PM is the current date and time.

Conclusion

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Bash Script : what does #!/bin/bash mean? [duplicate]

In bash script, what does #!/bin/bash at the 1st line mean ? UPDATE: Is there a difference between #!/bin/bash and #!/bin/sh ?

3 Answers 3

That is called a shebang, it tells the shell what program to interpret the script with, when executed.

In your example, the script is to be interpreted and run by the bash shell.

Some other example shebangs are:

#!/bin/sh — Execute the file using sh, the Bourne shell, or a compatible shell #!/bin/csh — Execute the file using csh, the C shell, or a compatible shell #!/usr/bin/perl -T — Execute using Perl with the option for taint checks #!/usr/bin/php — Execute the file using the PHP command line interpreter #!/usr/bin/python -O — Execute using Python with optimizations to code #!/usr/bin/ruby — Execute using Ruby 

and a few additional ones I can think off the top of my head, such as:

In a script with the bash shebang, for example, you would write your code with bash syntax; whereas in a script with expect shebang, you would code it in expect syntax, and so on.

Response to updated portion:

It depends on what /bin/sh actually points to on your system. Often it is just a symlink to /bin/bash . Sometimes portable scripts are written with #!/bin/sh just to signify that it’s a shell script, but it uses whichever shell is referred to by /bin/sh on that particular system (maybe it points to /bin/bash , /bin/ksh or /bin/zsh )

@ShivanRaptor #!/bin/bash Means run this script in bash. #!/bin/sh means run this script in sh which is the default unix shell, which might be bash or any other variant like ksh, dash, zsh, etc

When bash is run as sh , it behaves differently (more POSIX-like) than when it is run as bash . Read the manual; it does cover that detail.

@KarthikT it doesn’t run the default shell, it runs bash in Bourne Shell mode. (as opposed to Bourne Again Shell, aka. bash) On some older systems it would run Bourne Shell itself.

In bash script, what does #!/bin/bash at the 1st line mean ?

In Linux system, we have shell which interprets our UNIX commands. Now there are a number of shell in Unix system. Among them, there is a shell called bash which is very very common Linux and it has a long history. This is a by default shell in Linux.

When you write a script (collection of unix commands and so on) you have a option to specify which shell it can be used. Generally you can specify which shell it wold be by using Shebang(Yes that’s what it’s name).

So if you #!/bin/bash in the top of your scripts then you are telling your system to use bash as a default shell.

Now coming to your second question :Is there a difference between #!/bin/bash and #!/bin/sh ?

The answer is Yes. When you tell #!/bin/bash then you are telling your environment/ os to use bash as a command interpreter. This is hard coded thing.

Every system has its own shell which the system will use to execute its own system scripts. This system shell can be vary from OS to OS(most of the time it will be bash. Ubuntu recently using dash as default system shell). When you specify #!/bin/sh then system will use it’s internal system shell to interpreting your shell scripts.

Visit this link for further information where I have explained this topic.

Hope this will eliminate your confusions. good luck.

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What are SH Files and How to Execute Them?

Script files contain commands that are executed by a certain program or scripting engine. These commands are executed without being compiled. Instructions are written in scripting languages for run time environment. There are many scripting languages with different purposes and environments. However, the one we are going to discuss in this article is a bash scripting language that is used to work in Linux. The files containing the commands or syntax of bash scripting language are also known as SH files or Shell Script files.

What are SH Files in Linux?

Script files are known to be created and saved in the bash language because the instructions it contains are written in that language and it comes with an extension of .sh. Any command that you want to normally run in Terminal can be put into a script file to execute them. If you have a sequence of commands that you want to execute frequently then you can put it into a script and just call the script.

It is not important for a script file to have an extension of .sh. Linux is not Windows, because the first line of code called ‘shebang‘ in the file will be enough to ensure it as a script file for the programs. It’s a common convention to use a .sh extension for shell scripts but it’s not a useful convention. Putting the extension for the advantage of noticing the file as a script is not much and it will also lose the flexibility.

How to Create an SH File?

Just like other coded files created in the simple text editor, this can be done the same. All you need to know is the commands and syntax for the language to create one. However, the most important thing for the bash shell script file is that it starts with a shebang that is shown below:

This will be added to the first line of code to make a bash script executable. You can also check the location of bash interpreter by the following command:

Also, we need to use another command so that the system will recognize permission for this as an executable file. However, this might not be required in some cases:

Note: Filename can be any name that you give to your file.

Executing SH Files through Terminal in Linux

You can execute SH files if text commands are typed within the Terminal. The syntax of code in your SH file must be correct before executing it. We are just using sample code to demonstrate; how the script file works. You can have a different code that you are working on.

1. Open any text editor that you prefer on your system.
2. Now type the following sample code and save it with or without sh extension:

#!/bin/bash echo Hello, appuals users! #echo is used to display the line of text echo What is your name? #Program will ask for input echo what #Here user need to give input echo Hello, $what! #Input will be printed with text

Note: Read comments to understand each line of sample code.

Now open Terminal by pressing Ctrl + Alt + T keys altogether.

There are several commands to run/execute the script file:

Note: Name of file can be anything. Here we name the script file as “appuals” without any extension. Also, make sure you are in the correct directory where the file is located.
If the file is not executing then type the chmod command to make the system recognize the permission for this executable file. If the system already recognizes it as an executable file then skip this step:

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