Creating a script file (.sh) in Bash Scripting - Visual Walkthrough

Concept Flow - Creating a script file (.sh)

Open text editor

↓

Write script lines

↓

Save file with .sh extension

↓

Make file executable

↓

Run script in terminal

↓

See output or result

This flow shows how to create a shell script file, make it executable, and run it to see the output.

Execution Sample

Bash Scripting

#!/bin/bash

echo "Hello, world!"

This script prints 'Hello, world!' to the terminal when run.

Execution Table

Step	Action	Command/Code	Result/Output
1	Open text editor	nano hello.sh	Text editor opens with new file
2	Write script lines	#!/bin/bash echo "Hello, world!"	Script content written in editor
3	Save file	Ctrl+O then Enter	File 'hello.sh' saved
4	Exit editor	Ctrl+X	Back to terminal
5	Make file executable	chmod +x hello.sh	File permission changed to executable
6	Run script	./hello.sh	Hello, world!
7	End	Script finished running	Terminal prompt returns

💡 Script runs once and ends after printing the message.

Variable Tracker

Variable	Start	After Step 2	After Step 5	After Step 6
script_file	none	hello.sh content written in editor	hello.sh marked executable	script executed, output shown

Key Moments - 3 Insights

Why do we add #!/bin/bash at the top of the script?

This line tells the system to use the bash shell to run the script, as shown in execution_table step 2.

Why do we need to run chmod +x before running the script?

chmod +x makes the script file executable, allowing the system to run it, as seen in execution_table step 5.

What happens if we try to run the script without ./ before the filename?

The system may not find the script because current directory is not in PATH; using ./hello.sh runs it explicitly, shown in step 6.

Visual Quiz - 3 Questions

Look at the execution table, what command makes the script file executable?

A ./hello.sh

B chmod +x hello.sh

C nano hello.sh

D echo "Hello, world!"

💡 Hint

Check step 5 in the execution_table where file permissions change.

At which step does the script actually run and print output?

A Step 2

B Step 4

C Step 6

D Step 1

💡 Hint

Look for the step where './hello.sh' is executed and output appears.

If you forget to add #!/bin/bash at the top, what might happen?

A Script may run with a different shell or error

B Script runs normally without any issue

C chmod +x will fail

D File won't save

💡 Hint

Refer to key_moments about the purpose of the shebang line.

Concept Snapshot

#!/bin/bash at top tells system to use bash
Write commands in plain text editor
Save file with .sh extension
Make executable with chmod +x
Run script with ./filename.sh
Script runs and shows output in terminal

Full Transcript

To create a shell script file, first open a text editor like nano. Write your script lines, starting with #!/bin/bash to specify the shell. Save the file with a .sh extension, for example hello.sh. Exit the editor and make the file executable by running chmod +x hello.sh in the terminal. Finally, run the script by typing ./hello.sh. The script will execute and print its output, such as 'Hello, world!'. This process ensures your script runs correctly in the bash shell.

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