First Bash script in Bash Scripting

Introduction

A Bash script lets you tell your computer to do tasks automatically. It saves time and avoids mistakes when doing the same steps again and again.

You want to open several programs at once without clicking each one.

You need to rename many files with a pattern quickly.

You want to check your computer's disk space regularly.

You want to automate backups of important files.

You want to run a set of commands every time you start your computer.

Syntax

Bash Scripting

#!/bin/bash

echo "Hello, world!"

#!/bin/bash tells the computer this is a Bash script.

echo prints text on the screen.

Examples

This prints a welcome message.

Bash Scripting

#!/bin/bash

echo "Welcome to my script!"

This prints the current date using a command inside the script.

Bash Scripting

#!/bin/bash

# This is a comment

echo "Today is $(date)"

Sample Program

This script prints the classic greeting message to the screen.

Bash Scripting

#!/bin/bash

# Print a greeting message
echo "Hello, world!"

Important Notes

Make sure to give your script permission to run by typing chmod +x scriptname.sh.

Run your script by typing ./scriptname.sh in the terminal.

Comments start with # and help explain your code.

Summary

Bash scripts automate tasks by running commands in order.

Start scripts with #!/bin/bash to tell the system to use Bash.

Use echo to show messages on the screen.

Practice

1. What is the purpose of the first line #!/bin/bash in a Bash script?

easy

A. It comments out the first line so it is ignored.

B. It prints a welcome message when the script runs.

C. It sets the script to run in the background automatically.

D. It tells the system to use the Bash shell to run the script.

Solution

1. Step 1: Understand the shebang line

   The line #!/bin/bash is called a shebang and tells the system which interpreter to use.

2. Step 2: Identify its role in script execution

   This line ensures the script runs with the Bash shell, not another shell or program.

3. Final Answer:

   It tells the system to use the Bash shell to run the script. -> Option D

4. Quick Check:

   Shebang = Bash interpreter [OK]

Hint: Shebang line always points to the shell interpreter [OK]

Common Mistakes:

• Thinking it prints a message
• Confusing it with a comment
• Assuming it runs script in background

2. Which of the following is the correct way to print "Hello, World!" in a Bash script?

easy

A. echo "Hello, World!"

B. printf(Hello, World!)

C. console.log("Hello, World!")

D. print("Hello, World!")

Solution

1. Step 1: Identify the Bash command for output

   In Bash, echo is used to print text to the screen.

2. Step 2: Check syntax correctness

   echo "Hello, World!" correctly prints the message with quotes around the string.

3. Final Answer:

   echo "Hello, World!" -> Option A

4. Quick Check:

   Print command in Bash = echo [OK]

Hint: Use echo to print text in Bash scripts [OK]

Common Mistakes:

• Using print() like in Python
• Using console.log() from JavaScript
• Missing quotes in printf

3. What will be the output of this Bash script?

#!/bin/bash
echo "Start"
echo "End"

medium

A. Start\nEnd

B. Start
End (two lines)

C. Start
End

D. Start End

Solution

1. Step 1: Understand echo behavior

   The echo command prints text followed by a new line by default.

2. Step 2: Analyze the script output

   Two echo commands print "Start" and "End" each on its own line.

3. Final Answer:

   Start End (two lines) -> Option B

4. Quick Check:

   echo adds newline = two lines output [OK]

Hint: Each echo prints on a new line by default [OK]

Common Mistakes:

• Thinking echo prints on same line
• Confusing \n as literal text
• Ignoring new line after echo

4. Identify the error in this Bash script:

#!/bin/bash
echo Hello World

medium

A. Missing quotes around Hello World

B. echo command is misspelled

C. No error, script runs fine

D. Missing shebang line

Solution

1. Step 1: Check script syntax

   The script has a correct shebang line and uses echo properly.

2. Step 2: Understand echo argument rules

   Quotes are optional if no special characters or spaces that confuse shell; here it works fine.

3. Final Answer:

   No error, script runs fine -> Option C

4. Quick Check:

   echo without quotes works here [OK]

Hint: Quotes optional if no special chars or spaces [OK]

Common Mistakes:

• Assuming quotes are always required
• Thinking shebang is missing
• Believing echo is misspelled

5. You want to write a Bash script that prints your name and then the current date. Which script below will do this correctly?

hard

A. #!/bin/bash
echo "My name is Alice"
date

B. #!/bin/bash
print "My name is Alice"
date

C. #!/bin/bash
echo My name is Alice
current_date

D. #!/bin/bash
echo "My name is Alice"; date %Y-%m-%d

Solution

1. Step 1: Check commands for printing text and date

   echo prints text; date prints current date and time.

2. Step 2: Verify script correctness

   #!/bin/bash echo "My name is Alice" date uses echo correctly and calls date without errors.

3. Final Answer:

   #!/bin/bash\necho "My name is Alice"\ndate -> Option A

4. Quick Check:

   Use echo and date commands correctly [OK]

Hint: Use echo for text and date command for current date [OK]

Common Mistakes:

• Using print instead of echo
• Calling undefined commands like current_date
• Incorrect date command syntax