Creating a script file (.sh) in Bash Scripting

Introduction

A script file (.sh) lets you save commands to run them easily anytime without typing again.

You want to automate daily tasks like backups.

You need to run a set of commands repeatedly.

You want to share a set of commands with a friend or colleague.

You want to organize commands for a project in one place.

You want to run commands on a remote server automatically.

Syntax

Bash Scripting

#!/bin/bash

# Your commands go here

The first line #!/bin/bash tells the system to use the bash shell to run the script.

Make sure to give your script file execute permission with chmod +x filename.sh.

Examples

A simple script that prints Hello, world! to the screen.

Bash Scripting

#!/bin/bash

echo "Hello, world!"

A script that lists files in the /home/user directory.

Bash Scripting

#!/bin/bash

ls -l /home/user

A script that shows the current date and time.

Bash Scripting

#!/bin/bash

# This script shows the current date and time
date

Sample Program

This script prints a welcome message when run.

Bash Scripting

#!/bin/bash

# This script greets the user

echo "Welcome to your script!"

Important Notes

Always start your script with #!/bin/bash to ensure it runs with bash.

Use chmod +x yourscript.sh to make the script executable.

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

Summary

A .sh file saves commands so you can run them anytime.

Start with #!/bin/bash to tell the system how to run it.

Make the file executable with chmod +x before running.

Practice

1. What is the main purpose of creating a .sh script file in bash?

easy

A. To compile programs

B. To store text documents

C. To save a list of commands to run them later easily

D. To create image files

Solution

1. Step 1: Understand what a script file is

   A .sh file contains bash commands saved to run multiple times without typing again.

2. Step 2: Identify the purpose of saving commands

   Saving commands helps automate tasks and avoid retyping, which matches To save a list of commands to run them later easily.

3. Final Answer:

   To save a list of commands to run them later easily -> Option C

4. Quick Check:

   Script file purpose = save commands [OK]

Hint: Scripts save commands to run anytime without retyping [OK]

Common Mistakes:

• Thinking .sh files are for text or images
• Confusing scripts with compiled programs
• Not knowing scripts automate commands

2. Which line should you add at the very top of a bash script file to specify the interpreter?

easy

A. #!/bin/python

B. #!/bin/bash

C. #!/usr/bin/node

D. #!/bin/shutdown

Solution

1. Step 1: Identify the correct shebang for bash scripts

   The shebang line tells the system which program runs the script. For bash, it is #!/bin/bash.

2. Step 2: Eliminate incorrect interpreters

   Options A, C, and D point to other interpreters or invalid commands.

3. Final Answer:

   #!/bin/bash -> Option B

4. Quick Check:

   Shebang for bash = #!/bin/bash [OK]

Hint: Use #!/bin/bash as first line to run bash scripts [OK]

Common Mistakes:

• Using wrong interpreter path
• Forgetting the #! at the start
• Confusing bash with other languages

3. What will be the output when you run this script named greet.sh?

#!/bin/bash
echo "Hello, $USER!"

medium

A. Syntax error

B. Hello, root!

C. Hello, $USER!

D. Hello, your-username!

Solution

1. Step 1: Understand the variable $USER in bash

   $USER is an environment variable that holds the current user's username.

2. Step 2: Predict the echo output

   The echo command prints "Hello, " followed by the username, so it outputs "Hello, your-username!" where your-username is the actual user.

3. Final Answer:

   Hello, your-username! -> Option D

4. Quick Check:

   $USER expands to username = Hello, your-username! [OK]

Hint: Variables like $USER show your username in scripts [OK]

Common Mistakes:

• Thinking $USER prints literally
• Expecting 'root' always
• Confusing syntax causing errors

4. You wrote a script myscript.sh but when you run ./myscript.sh, it says Permission denied. What is the likely fix?

medium

A. Run chmod +x myscript.sh to make it executable

B. Add #!/bin/bash at the top

C. Rename the file to myscript.txt

D. Run the script with bash myscript.sh only

Solution

1. Step 1: Understand the cause of 'Permission denied'

   This error usually means the file is not executable by the user.

2. Step 2: Make the script executable

   Using chmod +x myscript.sh adds execute permission, allowing ./myscript.sh to run.

3. Final Answer:

   Run chmod +x myscript.sh to make it executable -> Option A

4. Quick Check:

   Permission denied fix = chmod +x [OK]

Hint: Use chmod +x to allow script execution [OK]

Common Mistakes:

• Forgetting to make script executable
• Only adding shebang without permissions
• Renaming file instead of fixing permissions

5. You want to create a script backup.sh that prints "Backup started" and then lists files in the current directory. Which script content is correct?

hard

A. #!/bin/bash
echo "Backup started"
ls

B. echo "Backup started"
ls
#!/bin/bash

C. #!/bin/bash
echo Backup started
ls-l

D. #!/bin/sh
echo "Backup started"
list

Solution

1. Step 1: Check the shebang and commands order

   The script must start with #!/bin/bash to run in bash, then commands follow in order.

2. Step 2: Verify commands and syntax

   #!/bin/bash echo "Backup started" ls has correct shebang, echo with quotes, and ls command to list files. Others have wrong order, missing quotes, or invalid commands.

3. Final Answer:

   #!/bin/bash echo "Backup started" ls -> Option A

4. Quick Check:

   Correct script structure = #!/bin/bash echo "Backup started" ls [OK]

Hint: Start script with #!/bin/bash then commands line by line [OK]

Common Mistakes:

• Placing shebang after commands
• Using wrong commands like 'list'
• Missing quotes around strings