What is Shell Scripting?

Introduction to Shell Scripting

Shell scripting is used for automating repetitive tasks by executing a sequence of commands in a script file. You can use it for managing files, scheduling tasks, and controlling system operations. It runs in a command-line environment, processing instructions step by step. Shell scripts improve efficiency by reducing manual input and streamlining workflows.

What are Shell Scripts?

Shell Script Meaning

A shell script is simply a file that contains a list of commands you want the system to run automatically. Instead of typing each command one by one in the terminal, you can put them together in a script and execute them at once.

It’s often used for tasks like managing files, running programs, monitoring system performance, or automating routine jobs. Shell scripts make daily system work easier, faster, and less prone to mistakes.

Types of Shell Scripting

Shell scripting can be categorized as per the shell interpreter you use. Although each shell has its own set of capabilities, they all serve the same purpose: to execute commands and automate processes in Unix/Linux systems.

Bourne Shell (sh) Scripting

Choose Bourne Shell (sh) if you prefer simplicity and compatibility across Unix systems. It is efficient but lacks many advanced features found in modern shells.

Bourne Again Shell (Bash) Scripting

Bash is an improved version of Bourne Shell and acts as the default shell in most Linux distributions. You get features like command-line editing, better scripting capabilities, and improved performance.

C Shell (csh) Scripting

If you prefer C-like syntax, you might use C Shell. It offers features like aliasing and command history but is less common today due to its scripting limitations.

Korn Shell (ksh) Scripting

Korn Shell gives you better scripting capabilities and performance by combining features from both Bourne and C shells, many enterprises use it for its speed and efficiency.

Z Shell (zsh) Scripting

With Z Shell gives you advanced features like auto-completion, spelling correction, and improved customization. Developers and power users favor it for its flexibility.

Although there are multiple shell options, Bash remains the most widely used due to its flexibility and widespread support.

How Does Shell Script Work?

Shell scripts work by executing a series of commands within a Unix shell, which serves as a command-line interpreter for the operating system. These scripts work involves a series of steps like writing, accessing, and executing a script.

• Write the script: Shell script consists of a series of commands written in a language that shell can interpret which also includes loops, variables, and if-then-else statements. You can also add Comments to increase readability. The first line of the script often specifies the interpreter to use (e.g., `#!/bin/bash`).
• Make the script accessible: Once the script is written, it is saved with a `.txt` or `.sh` file extension in a location accessible to the shell.
• Set and execute permissions: Before the script can be run, you must read and execute permissions for the file. Use the `chmod` command to set these permissions. 

For example, chmod +x basic_script.sh gives the current user executable permissions.

To run a shell script in the current environment without creating a new process, use the `source` command. When the script runs other programs, these are also processes. All processes are related, and a command executed in the shell is a child process of the shell.

Advantages of Shell Scripting

Some of the advantages of shell scripting are:

• Shell scripting is suitable for professionals, especially system administrators, DevOps developers and related professionals.
• It has the ability to automate repetitive tasks and improve productivity.
• It is ideal for rapidly prototyping heavy applications.
• They are highly portable and are compatible to run on any UNIX-like system with minimum modifications.
• They are generally simple to create, modify and debug.

Disadvantages of Shell Scripting

Some of the disadvantages of shell scripting are:

• Scripted languages may face more expensive errors than other programming languages.
• Shell scripting could be slower than programs written in compiled languages and less suited for heavy computational tasks.
• Other platforms associated with shell scripting are not always compatible.

Shell Script Commands

Shell script commands are used to automate tasks in a Unix/Linux terminal. Here are some commonly used commands:

1. File & Directory Management

• ls – List files and directories
• pwd – Print current working directory
• cd directory_name – Change directory
• mkdir new_directory – Create a new directory
• rm file_name – Delete a file
• rm -r directory_name – Delete a directory and its contents
• cp source destination – Copy files or directories
• mv old_name new_name – Rename or move files/directories

2. File Permissions & Ownership

• chmod 755 file_name – Change file permissions
• chown user:group file_name – Change file owner

3. Process Management

• ps – View running processes
• top – Monitor system processes

4. Networking

• curl URL – Fetch data from a URL
• wget URL – Download a file

5. Text Processing

• cat file_name – Display file contents
• grep ‘text’ file_name – Search for text in a file
• sed ‘s/old/new/g’ file_name – Replace text in a file
• awk ‘{print $1}’ file_name – Extract columns from a file

Explore the full article for installing Perl 5.28 on an Arch Linux Webserver with all the details.

Basics of Shell Scripting in Linux

Creating and Running a Shell Script

Step 1: Create a Script File

A shell script is a text file with a .sh extension.

nano myscript.sh

Step 2: Add the Shebang (#!)

Every shell script starts with a shebang (#!) to specify the shell interpreter.

#!/bin/bash
echo "Hello, World!"

Step 3: Give Execute Permission

Before running the script, you need to make it executable.

chmod +x myscript.sh

Step 4: Run the Script

Execute the script using the command below:

./myscript.sh

Function with Arguments

You can pass arguments to a function when calling it.

Example: Function with One Argument.

#!/bin/bash

great(){
	echo "Hello, $1!"
}

# Calling the function with an argument
greet "Alice"

Output:

Hello, Alice!

Example: Function with Multiple Arguments

#!/bin/bash

add_numbers(){
	sum=$(( $1 + $2 ))
	echo "Sum: $sum"
}

# Calling the function with two arguments
add_numbers 10 20

Output:

Sum: 30

Variables in Shell Scripting

Variables store data values.

#!/bin/bash

name="Cantech"

echo "$name the web hosting company."

Using Special Variables in Functions

• $1, $2, … – Positional parameters (arguments)
• $# – Number of arguments passed
• $@ – All arguments as separate words
• $* – All arguments as a single string
• return – Return an exit status (0 for success, nonzero for failure)

Example: Counting Arguments

#!/bin/bash

  count_args() {

	echo "Number of arguments: $#"
	echo "All arguments: $@"
}

count_args "Cantech" "Cantech.Cloud"

Output:

Number of arguments: 2
All arguments: Cantech Cantech.Cloud

Function with Conditional Statements:

#!/bin/bash

  check_even_odd() {

	if (( $1 % 2 == 0)); then
		echo "$1 is even."
	else
		echo "$1 is odd."
}

check_even_odd 5
check_even_odd 12

Output:

5 is odd.
12 is even.

Shell scripting gives you the power to automate tasks, manage systems efficiently, and boost productivity in a Linux environment. By using commands, functions, and conditionals, you can simplify complex operations and save time.

Explore the full article to display the current working directory in Linux using the pwd command with all the details.

Conclusion

Shell scripting is used to automate manual tasks. It is very useful for most repetitive tasks which are time consuming to execute or schedule using one line at a time. By turning a series of commands into a script, system administrators can save a lot of time, improve accuracy, and simplify complex tasks.

FAQs

What is shell scripting used for?

Shell scripting helps in automating tasks, manages files, schedules jobs, and simplifies system administration. It facilitates the execution of multiple commands efficiently with minimal manual effort.

What is Unix and shell scripting?

Unix is an operating system known for its stability and multitasking capabilities. Shell-scripting in Unix allows you to write and execute command sequences to automate processes.

Is shell scripting a language?

Shell scripting is not a standalone programming language but a way to use shell commands in a structured script. It supports programming concepts like loops, conditionals, and functions.

What is shell programming?

Shell programming means writing simple scripts to automate tasks on a system. It helps you run commands, manage files, and perform routine operations automatically using the system shell.

What is linux shell scripting?

Linux shell scripting means writing simple commands in a file to automate tasks on a Linux system. Instead of running commands one by one, a script runs them together, saving time and reducing manual work. It is commonly used for system tasks like backups, file management, and server maintenance.

Is shell scripting easy?

Yes, shell scripting is relatively easy to learn, especially if you’re familiar with Linux commands. With practice, you can quickly automate tasks and improve system efficiency.