README.md

Shell Scripting: Automating with the Command Line

Shell scripting helps automate repetitive tasks using command-line instructions. This section covers a beginner-friendly project to create directories and user accounts using a shell script on an Ubuntu server.

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📁 Step-by-Step: Create and Execute a Shell Script

1. Create a Directory for Your Script

mkdir shell-scripting
cd shell-scripting

2. Create a Script File Using vim

vim my_first_shell_script.sh

Paste this code into the file:

#!/bin/bash

# Create directories
mkdir Folder1
mkdir Folder2
mkdir Folder3

# Create users
sudo useradd user1
sudo useradd user2
sudo useradd user3

3. Confirm Script Exists

ls -latr

🔒 Check File Permissions

Use ls -l to view permissions:

ls -l my_first_shell_script.sh

Expected output: -rw-r--r-- (No execute permission)

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🚫 Try to Execute (Expect Failure)

./my_first_shell_script.sh

You should see: bash: ./my_first_shell_script.sh: Permission denied

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✅ Fix Permissions and Re-run

chmod +x my_first_shell_script.sh
./my_first_shell_script.sh

✅ Verify Results

Check folders:

ls

Expected: Folder1 Folder2 Folder3

Check users:

id user1
id user2
id user3

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⚡ Error Handling in Shell Scripts

To make scripts robust and avoid errors when folders or users already exist, we use checks like:

[ ! -d "$dir" ] && mkdir "$dir"           # Only create if folder doesn't exist
id "$user" &>/dev/null || useradd "$user" # Only add user if not found

This prevents crashes and makes your scripts reusable and reliable.

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⚠️ Troubleshooting & Common Issues

Problem	Cause	Solution
Permission denied when running script	File isn’t marked executable	Run: chmod +x my_first_shell_script.sh
command not found: vim	Vim editor isn’t installed	Run: sudo apt install vim
useradd: user already exists	You’ve already created the user	Run: sudo deluser user1 before re-running script
mkdir: cannot create directory	Folder already exists	Use rm -r Folder1 before running the script again
No output or visible effect	Commands are being silently executed	Add echo statements to print progress, or use set -x to debug

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🫠 What is a Shebang?

At the top of your script:

#!/bin/bash

This line tells the system to use the Bash shell to run your script. It’s called a shebang.

❀ Significance of Shebang

• Defines the Interpreter: Ensures the correct shell (e.g., bash, sh, zsh) is used.
• Enables Portability: Scripts run consistently across different systems.
• Avoids Confusion: Without it, the system might not execute the script as expected.

Alternative example:

#!/bin/sh   # for POSIX-compliant shell

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🤖 Script Debugging with set -x

To trace and debug script execution:

#!/bin/bash
set -x   # Enable debugging

# Commands here...

Use Cases:

• Logs each command before execution.
• Helps trace failures or logic bugs.

You can disable debugging mid-script with:

set +x

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🔤 Shell Variables

Declare:

name="John"

Use:

echo $name

Output:

John

Variables store data like strings or numbers. echo is used to display them.

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🏁 Conclusion

This hands-on scripting task demonstrated how to automate folder and user creation, manage permissions, and use variables in Bash. Shell scripting is essential for every DevOps engineer—helping you automate, replicate, and scale tasks efficiently.

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