Function definition in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function in bash scripting?

A function is a named block of code that performs a specific task and can be reused multiple times in a script.

beginner

How do you define a function named greet in bash?

You can define it like this:

greet() {
  echo "Hello!"
}

beginner

How do you call a function named greet in bash?

Just write the function name without parentheses:

greet

intermediate

Can bash functions accept arguments? How?

Yes, bash functions accept arguments which are accessed inside the function as $1, $2, etc., representing the first, second argument, and so on.

intermediate

What is the purpose of the return statement in a bash function?

The return statement ends the function and optionally sends an exit status (a number between 0 and 255) back to the caller.

How do you start defining a function named say_hello in bash?

A def say_hello():

B function say_hello[] {

C function say_hello()

D say_hello() {

In bash, functions are defined with the syntax: function_name() { ... }

Inside a bash function, how do you access the first argument passed to it?

A $0

B $first

C $1

D $arg1

Arguments inside bash functions are accessed as $1, $2, etc. $0 is the script name.

What does the return statement do inside a bash function?

A Prints a value to the screen

B Ends the function and sets an exit status

C Calls another function

D Defines a new variable

return ends the function and optionally sends an exit status back.

Which of these is a correct way to call a bash function named greet?

A greet

B greet()

C call greet

D run greet

You call a bash function simply by writing its name: greet

What symbol is used to start the body of a bash function?

A {

B [

C (

D <

The function body starts with a curly brace { and ends with }

Explain how to define and call a function in bash, including how to pass and use arguments.

Think about how you tell a friend to do a task and give them some details.

Describe the role of the return statement in a bash function and how it differs from outputting text.

Return is like finishing a task and giving a status, echo is like saying something out loud.

Practice

1. What is the correct way to define a function named greet in bash?

easy

A. greet() { echo "Hello"; }

B. function greet[] { echo "Hello"; }

C. def greet() { echo "Hello"; }

D. function greet() echo "Hello"

Solution

1. Step 1: Understand bash function syntax

   Bash functions are defined using either name() { commands; } or function name { commands; }.

2. Step 2: Check each option

   greet() { echo "Hello"; } uses the correct syntax with parentheses and braces. Options B, C, and D have syntax errors or use wrong keywords.

3. Final Answer:

   greet() { echo "Hello"; } -> Option A

4. Quick Check:

   Function syntax = greet() { ... } [OK]

Hint: Use parentheses and braces to define bash functions [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Using Python 'def' keyword
• Omitting braces around commands

2. Which of the following is a valid function definition syntax in bash?

easy

A. function myFunc() { echo "Hi"; }

B. myFunc[] { echo "Hi"; }

C. function myFunc[] echo "Hi"

D. myFunc() echo "Hi"

Solution

1. Step 1: Recall valid bash function syntax

   Bash allows defining functions as function name() { commands; } or name() { commands; }.

2. Step 2: Evaluate options

   function myFunc() { echo "Hi"; } matches valid syntax. Options A and C use square brackets incorrectly. myFunc() echo "Hi" misses braces around commands.

3. Final Answer:

   function myFunc() { echo "Hi"; } -> Option A

4. Quick Check:

   Valid syntax includes 'function name() { ... }' [OK]

Hint: Remember to use braces {} to group commands in functions [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Omitting braces after function name
• Missing parentheses after function name

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

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

medium

A. Error: function not found

B. Hello, Alice!

C. say_hello Alice

D. Hello, $1!

Solution

1. Step 1: Understand function call with argument

   The function say_hello takes one argument and prints it using $1.

2. Step 2: Substitute argument and print

   Calling say_hello Alice replaces $1 with "Alice", so output is "Hello, Alice!".

3. Final Answer:

   Hello, Alice! -> Option B

4. Quick Check:

   Function argument $1 = Alice [OK]

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

Common Mistakes:

• Printing literal $1 instead of its value
• Forgetting to call the function
• Syntax errors in function definition

4. Identify the error in this bash function definition:

function greet {
  echo "Hi"
}

medium

A. Missing parentheses after function name

B. Missing braces around commands

C. Missing semicolon after echo

D. No error; parentheses are optional with 'function' keyword

Solution

1. Step 1: Check function syntax with 'function' keyword

   Bash allows function name() { commands; } or function name { commands; }. Parentheses after the name are optional.

2. Step 2: Identify if there's an error

   The code function greet { echo "Hi"; } is valid syntax.

3. Final Answer:

   No error; parentheses are optional with 'function' keyword -> Option D

4. Quick Check:

   function name { ... } [OK]

Hint: Parentheses () are optional with 'function name' [OK]

Common Mistakes:

• Omitting parentheses after function name
• Confusing braces and parentheses
• Assuming semicolon needed after echo

5. You want to create a bash function sum that takes two numbers and prints their sum. Which function definition correctly does this?

hard

A. function sum { echo $1 + $2; }

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

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

D. sum() { echo $1 $2; }

Solution

1. Step 1: Understand arithmetic in bash functions

   To add numbers, use arithmetic expansion $(()) inside echo.

2. Step 2: Evaluate each option

   sum() { echo $(($1 + $2)); } correctly sums $1 and $2 using $(($1 + $2)). Options A and B print strings with plus sign, not sum. sum() { echo $1 $2; } prints numbers without adding.

3. Final Answer:

   sum() { echo $(($1 + $2)); } -> Option C

4. Quick Check:

   Use $(()) for arithmetic in bash functions [OK]

Hint: Use $(()) to perform math inside bash functions [OK]

Common Mistakes:

• Printing variables without arithmetic expansion
• Omitting parentheses for function definition
• Using 'function' without parentheses