Calling functions in Bash Scripting - Mini Project: Build & Apply

Calling functions

📖 Scenario: You are writing a simple bash script to organize tasks into functions. Functions help you reuse code and keep your script clean.

🎯 Goal: Create a bash script with a function that prints a greeting message. Then call that function to show the message.

📋 What You'll Learn

Create a function named greet that prints the text Hello, welcome to bash scripting!

Call the function greet after its definition

💡 Why This Matters

🌍 Real World

Functions in bash scripts help organize tasks like backups, monitoring, or automation steps. Calling functions makes scripts easier to read and reuse.

💼 Career

Knowing how to write and call functions in bash is essential for system administrators, DevOps engineers, and anyone automating tasks on Linux or Unix systems.

1

Create the greet function

Write a bash function named greet that prints the exact text Hello, welcome to bash scripting! using echo. Use the syntax: greet() { ... }

Bash Scripting

# Define the greet function here
greet() {
    # Your code here
}

Hint

Use echo inside the function to print the message.

2

Call the greet function

After the greet function definition, write a line to call the function by its name greet.

Bash Scripting

greet() {
    echo "Hello, welcome to bash scripting!"
}

# Call the greet function below
# Your code here

Hint

Just write the function name greet on a new line to call it.

3

Add a comment explaining the function call

Add a comment line before the function call that says # Call the greet function.

Bash Scripting

greet() {
    echo "Hello, welcome to bash scripting!"
}

# Your comment here
# Your code here

Hint

Comments start with # in bash scripts.

4

Run the script and show the output

Run the script and print the output. The output should be exactly Hello, welcome to bash scripting!

Bash Scripting

# Run the script and print the output
# Your code here

Hint

Run the script in your terminal using bash scriptname.sh or ./scriptname.sh if executable.

Practice

1. In Bash scripting, how do you call a function named greet?

easy

A. Write greet() with parentheses.

B. Write call greet().

C. Just write greet on a line by itself.

D. Write run greet.

Solution

1. Step 1: Understand Bash function call syntax

   In Bash, functions are called by simply writing their name without parentheses or keywords.

2. Step 2: Compare options with Bash syntax

   Only Just write greet on a line by itself. matches the correct way: just the function name alone.

3. Final Answer:

   Just write greet on a line by itself. -> Option C

4. Quick Check:

   Function call = function name alone [OK]

Hint: Call functions by name only, no parentheses needed [OK]

Common Mistakes:

• Adding parentheses like in other languages
• Using keywords like 'call' or 'run'
• Forgetting to write the function name

2. Which of the following is the correct syntax to define a function named hello in Bash?

easy

A. hello { echo "Hi" }

B. hello() { echo "Hi" }

C. def hello() { echo "Hi" }

D. function hello() echo "Hi"

Solution

1. Step 1: Recall Bash function definition syntax

   Bash functions are defined as name() { commands; } or with the keyword function followed by name and braces.

2. Step 2: Check each option

   hello() { echo "Hi" } uses hello() { echo "Hi" }, which is correct. hello { echo "Hi" } misses the () after the name. def hello() { echo "Hi" } uses Python syntax. function hello() echo "Hi" misses braces.

3. Final Answer:

   hello() { echo "Hi" } -> Option B

4. Quick Check:

   Function syntax = name() { commands } [OK]

Hint: Use name() { commands } to define functions in Bash [OK]

Common Mistakes:

• Using Python or other language syntax
• Omitting parentheses or braces
• Misplacing the function keyword

3. What is the output of this script?

say_hello() {
  echo "Hello, $1!"
}
say_hello Alice

medium

A. Hello, Alice!

B. Hello, $1!

C. say_hello Alice

D. Error: function not found

Solution

1. Step 1: Understand function and argument usage

   The function say_hello prints "Hello," followed by the first argument $1.

2. Step 2: Identify the argument passed

   The function is called with argument "Alice", so $1 becomes "Alice".

3. Final Answer:

   Hello, Alice! -> Option A

4. Quick Check:

   Function argument $1 = Alice [OK]

Hint: Use $1 to access first argument inside function [OK]

Common Mistakes:

• Printing literal $1 instead of its value
• Forgetting to pass argument
• Misunderstanding function call syntax

4. Identify the error in this script:

greet() {
  echo "Hi $name"
}
greet John

medium

A. Function greet is not defined correctly

B. Missing semicolon after echo

C. Function call syntax is wrong

D. Variable $name is not set or passed

Solution

1. Step 1: Check variable usage inside function

   The function uses $name, but no variable named name is set or passed.

2. Step 2: Check function call and argument passing

   The function is called with "John" as argument, but the function does not use $1 to access it.

3. Final Answer:

   Variable $name is not set or passed -> Option D

4. Quick Check:

   Use $1 to access arguments, not undefined variables [OK]

Hint: Use $1 inside function to get passed arguments [OK]

Common Mistakes:

• Using undefined variables instead of $1
• Assuming arguments auto-assign to variable names
• Ignoring function call syntax correctness

5. You want to write a Bash function sum that takes two numbers as arguments and prints their sum. Which script correctly calls the function and prints the result?

hard

A. sum() {
echo $(($1 + $2))
}
sum 3 5

B. sum() {
echo $1 + $2
}
sum 3 5

C. sum() {
echo $((1 + 2))
}
sum 3 5

D. sum() {
echo $1 $2
}
sum 3 5

Solution

1. Step 1: Understand arithmetic evaluation in Bash

   To add numbers, use $((expression)). Inside, use $1 and $2 for arguments.

2. Step 2: Check each option's output

   sum() {
     echo $(($1 + $2))
   }
   sum 3 5

   correctly sums $1 + $2.

   sum() {
     echo $1 + $2
   }
   sum 3 5

   prints literal string with plus sign.

   sum() {
     echo $((1 + 2))
   }
   sum 3 5

   adds 1 and 2 literally, ignoring arguments.

   sum() {
     echo $1 $2
   }
   sum 3 5

   prints arguments separated by space.

3. Final Answer:

   sum() { echo $(($1 + $2)) } sum 3 5 -> Option A

4. Quick Check:

   Use $(( $1 + $2 )) for sum [OK]

Hint: Use $(( $1 + $2 )) to add arguments inside function [OK]

Common Mistakes:

• Printing arguments without arithmetic evaluation
• Using fixed numbers instead of arguments
• Confusing string concatenation with addition