What is Shell Script?

Shell scripting involves writing a series of commands in a plain text file, often referred to as a Shell Script. These scripts are executed by a shell, which is a command-line interpreter. The most common shells include

  1. Bash (Bourne Again SHell)
  2. Zsh (Z Shell)
  3. Fish.

Shell scripts can range from simple one-liners to complex programs, and they are used to perform a wide variety of tasks, such as file manipulation, system administration, and automation of repetitive tasks.

Benefits of Shell Scripting:

  1. Automation: Shell scripts allow users to automate repetitive tasks, saving time and reducing the chance of human error.

  2. Customization: Users can create scripts tailored to their specific needs, providing a high degree of customization.

  3. Batch Processing: Shell scripts are excellent for handling batch processing tasks, where multiple commands need to be executed in sequence.

  4. System Administration: Shell scripts are commonly used for system administration tasks, such as backups, log rotation, and software installation.

Writing a Simple Shell Script:

Let’s create a basic shell script that prints a greeting message. Open a text editor and create a file named greeting.sh. Add the following lines:

#!/bin/bash
# This is a simple shell script

echo "Hello, welcome to the world of shell scripting!"

Save the file and make it executable by running the following command in the terminal:

chmod +x greeting.sh

Now, you can execute the script:

./greeting.sh

The output should be:

Hello, welcome to the world of shell scripting!

Running Shell Scripts on Ubuntu and Linux:

Now, we will discuss how to run a .sh file in Ubuntu and Linux.

  1. Make the Script Executable: Before running a shell script, ensure it is executable. Use the chmod command as shown earlier.

  2. Navigate to the Script Directory: Open a terminal and use the cd command to navigate to the directory containing your shell script.

  3. Run the Script: Execute the script by typing ./scriptname.sh in the terminal, replacing “scriptname” with the actual name of your script.

cd path/to/script
./greeting.sh
  1. Using the Bash Command: If your script begins with #!/bin/bash (known as a shebang), you can also run it using the bash command.
bash greeting.sh

What does $@ mean in Shell Script?

In shell script, $@ represents all the command-line arguments passed to script. It is often used to reference list of arguments as separate entities. When used within double quotes, like "$@", it preserves individual arguments, accounting for spaces and special characters.

Here is brief explanation:

  • $@: Represents all positional parameters (arguments) passed to script or function. Each argument is treated as separate word.

  • "$@": When double-quoted, preserves separation of arguments, allowing for spaces or special characters within individual arguments.

Here is simple example to illustrate:

#!/bin/bash

# Save this script as example.sh

echo "The total number of arguments is: $#"
echo "The arguments are: $@"
echo "The arguments with double quotes are: \"$@\""

When you run this script with arguments, for example:

bash example.sh arg1 "argument 2" arg3

It would output:

The total number of arguments is: 3
The arguments are: arg1 argument 2 arg3
The arguments with double quotes are: "arg1" "argument 2" "arg3"

As you can see, $@ represents all arguments, and "$@" preserves the individual arguments, even if they contain spaces.