What a shell script is in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a shell script?

A shell script is a text file that contains a series of commands for the shell to execute. It helps automate tasks on your computer.

beginner

Why use a shell script instead of typing commands one by one?

Shell scripts save time by running many commands automatically. They reduce mistakes and make repeating tasks easy.

beginner

What does the first line '#!/bin/bash' mean in a shell script?

It tells the computer to use the Bash shell to run the script. This line is called a shebang.

beginner

How do you run a shell script?

You make the script file executable and then run it by typing its path, like './script.sh'.

beginner

Can a shell script interact with the user?

Yes, shell scripts can ask for input and show messages, making them interactive.

What is the main purpose of a shell script?

A To automate a series of commands

B To design websites

C To edit images

D To play music

Shell scripts automate commands so you don't have to type them one by one.

What does the '#!/bin/bash' line do in a shell script?

A Ends the script

B Starts a comment

C Specifies the shell to run the script

D Runs the script automatically

This line tells the system to use Bash to run the script.

How do you make a shell script executable?

A By renaming it

B By running 'chmod +x script.sh'

C By opening it in a text editor

D By copying it

The 'chmod +x' command gives permission to run the script.

Which file extension is commonly used for shell scripts?

A .sh

B .doc

C .txt

D .exe

Shell scripts usually have the '.sh' extension.

Can shell scripts ask the user for input?

A No

B Only with special software

C Only in Windows

D Yes

Shell scripts can use commands like 'read' to get input from users.

Explain what a shell script is and why it is useful.

Think about how repeating tasks can be done faster.

Describe the steps to create and run a simple shell script.

Remember the commands to give permission and how to start the script.

Practice

1. What is a shell script in simple terms?

easy

A. A file containing commands that run automatically in the shell

B. A program that only runs on Windows

C. A type of hardware device

D. A graphical user interface for the computer

Solution

1. Step 1: Understand what a shell script is

   A shell script is a text file with commands that the shell can run automatically.

2. Step 2: Compare options to definition

   Only A file containing commands that run automatically in the shell describes a file with commands running automatically in the shell.

3. Final Answer:

   A file containing commands that run automatically in the shell -> Option A

4. Quick Check:

   Shell script = file with commands [OK]

Hint: Think: script means commands saved to run later [OK]

Common Mistakes:

• Confusing shell script with software programs
• Thinking shell scripts are hardware
• Believing shell scripts are graphical tools

2. Which of these is the correct way to start a shell script file?

easy

A.

B. #!/bin/bash

C. print('Hello World')

D. function main() {}

Solution

1. Step 1: Identify the shell script shebang

   The first line in a shell script usually starts with #!/bin/bash to tell the system to use bash shell.

2. Step 2: Check other options

   <!DOCTYPE html> is for HTML, print('Hello World') is Python, function main() {} is like JavaScript. None are shell script shebangs.

3. Final Answer:

   #!/bin/bash -> Option B

4. Quick Check:

   Shell scripts start with #!/bin/bash [OK]

Hint: Look for #! to start shell scripts [OK]

Common Mistakes:

• Using code from other languages as shell script start
• Omitting the shebang line
• Confusing shell script with HTML or Python

3. What will this shell script output?

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

medium

A. Error: command not found

B. echo "Hello, World!"

C. No output

D. Hello, World!

Solution

1. Step 1: Understand the echo command

   The echo command prints the text inside quotes to the screen.

2. Step 2: Predict the output

   The script will print exactly: Hello, World!

3. Final Answer:

   Hello, World! -> Option D

4. Quick Check:

   echo prints text = Hello, World! [OK]

Hint: echo prints text exactly as given [OK]

Common Mistakes:

• Thinking echo prints the command itself
• Expecting error without cause
• Assuming no output without running script

4. This shell script is supposed to print "Done" but it shows an error:

#!/bin/bash
echo Done

What is the likely problem?

medium

A. The shebang line is incorrect

B. The echo command is misspelled

C. The script file is missing execute permission

D. The script needs a semicolon after echo

Solution

1. Step 1: Check script permissions

   If the script shows an error when run, it might not have execute permission set.

2. Step 2: Verify other options

   Echo is correct, shebang is correct, and semicolon is not needed after echo.

3. Final Answer:

   The script file is missing execute permission -> Option C

4. Quick Check:

   Missing execute permission causes errors [OK]

Hint: Make script executable with chmod +x [OK]

Common Mistakes:

• Assuming syntax error without checking permissions
• Adding unnecessary semicolons
• Changing correct shebang line

5. You want to automate cleaning temporary files daily using a shell script. Which statement best describes what you should do?

hard

A. Write a shell script with commands to delete temp files, then schedule it with cron

B. Manually type delete commands every day in the terminal

C. Use a graphical tool only, no scripts needed

D. Write a shell script but run it only once manually

Solution

1. Step 1: Understand automation goal

   To automate daily cleaning, you need a script that runs commands automatically.

2. Step 2: Use scheduling tool

   Cron is a tool that runs scripts on a schedule, perfect for daily tasks.

3. Final Answer:

   Write a shell script with commands to delete temp files, then schedule it with cron -> Option A

4. Quick Check:

   Script + cron = daily automation [OK]

Hint: Combine script with cron for daily tasks [OK]

Common Mistakes:

• Thinking manual typing is automation
• Ignoring scheduling tools like cron
• Running script only once instead of daily