Writing a Bash Shell Script

Bash shell scripts in Linux are text files that contain a series of commands that can be executed by the Bash shell. Bash (Bourne Again Shell) is a popular shell in Linux and UNIX systems, and shell scripts are used to automate tasks, configure systems, or perform a sequence of operations.

How to Write a Bash Shell Script

1. Create a New File: You can create a new script using any text editor like nano, vim, or gedit.

   
   gedit myscript.sh
   

2. Write the Script: A basic shell script begins with a "shebang" (#!/bin/bash) to specify the interpreter that will be used to execute the script. The rest of the file contains the commands to be run.

   Example of a simple script:

   
   #!/bin/bash
   # This is a comment
   echo "Hello, World!"  # Print "Hello, World!"
   

   • #!/bin/bash: Specifies that the script will be executed using the Bash shell.
   • echo "Hello, World!": A command that prints the string "Hello, World!" to the terminal.
   • Comments: Any line starting with # is a comment and will not be executed.

3. Save and Close: After writing your script, save and exit the editor. You can give .sh extension to distinguish the script file but is not mandatory.

How to Make the Script Executable

After creating the script, you need to make it executable so the system knows it can run as a program.

chmod +x myscript.sh

This command gives execute permissions to the script.

How to Execute the Bash Script

You can execute the script by typing the following command:

./myscript.sh

• ./ indicates the current directory, and Bash will look for the myscript.sh file there.

Alternatively, you can also run the script by explicitly calling Bash to execute it:

bash myscript.sh

Example: A More Complex Script

Here's a script that takes a user's name as input and greets them:

#!/bin/bash
# A simple greeting script

echo "Enter your name:"
read name  # Read input from the user
echo "Hello, $name! Welcome to the world of shell scripting!"

In this script:

• read name: Reads input from the user and stores it in the variable name.
• $name: Refers to the value stored in the name variable.

Conclusion

Bash shell scripts are a powerful way to automate tasks on Linux systems. You write them by creating a plain text file, adding commands and logic, making the script executable, and then running it with Bash. The more you practice, the more you'll understand the syntax and capabilities of shell scripting.