Linux Shell Scripting

Linux shell scripting is a way to automate tasks in the Unix/Linux environment. A shell script is a text file containing a sequence of commands for a Unix-based operating system's shell to execute. Shell scripting is a powerful tool for automating tasks in a Linux environment. Using variables, control flow, functions, and input/output redirection, you can create scripts to perform a wide range of tasks efficiently. Always start your scripts with a shebang to specify the interpreter, and use comments to document your code for better readability and maintenance.

Why use Shell Scripts?

1. Automation
2. Efficiency
3. Customization
4. Reusability

Steps for Linux Shell Scripting

Step1: Get Manual Commands for the requirement

Step 2: Select any command line editor like vi, vim, and nano to write a script.

Step3: Write a Bash shell script - Now open a text file with anyName and with any extension but will take .sh just to represent that the text file is a shell script. - Write the first line as a shebang line (#!/bin/bash) - Paste all required commands in a sequence

Step4: Executing Bash Shell Script - Provide the Execution Permission using chmod +x script_name.sh - Run with ./script_name.sh or <complete_path>/script_name.sh

Simple User Creation Script

#!/bin/bash

# Check if the script is run as root
if ["$(id -u)" -ne 0]; then
        echo "This script must be run as root. Please run with sudo."
        exit 1
fi

# Prompt for the username
read -p "Enter the new username: " username

# Prompt for the password
read -s -p "Enter the password for $username: " password
echo

# Create the user
useradd -m -s /bin/bash "$username"

# Confirm if the user was created
echo "User $username has been created."

Steps to Execute the Script

1. Save the Script: Save the script to a file, e.g., create_user.sh.
2. Make the Script Executable: Run chmod +x create_user.sh.
3. Execute the Script with Root Privileges: Run sudo ./create_user.sh.

Script Breakdown

1. Check for Root Privileges: The script checks if it is run as root using $(id -u) -ne 0. If not, it exits with a message.
2. Prompt for Username: read -p "Enter the new username: " username prompts the user to enter the new username.
3. Prompt for Password: read -s -p "Enter the password for $username: " password prompts the user to enter the password without echoing it to the screen.
4. Prompt for Group: This step is optional. If the group is specified, the user will be added to this group.
5. Create the User: useradd -m -s /bin/bash "$username" creates a new user with a home directory and default shell.
6. Set the Password: echo "$username:$password" | chpasswd sets the password for the new user.
7. Add to Group: usermod -aG "$group" "$username" adds the user to the specified group if one was provided.