Function libraries (sourcing scripts) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to 'source' a script in Bash?

Sourcing a script means running it in the current shell session so that functions and variables defined in it become available immediately without starting a new shell.

beginner

How do you source a script named library.sh in Bash?

Use the command source library.sh or the shorthand . library.sh to include the script in the current shell session.

beginner

Why use function libraries in Bash scripting?

Function libraries let you reuse code easily by keeping common functions in one file. You can source this file in many scripts to avoid rewriting the same code.

intermediate

What happens if you run a script normally instead of sourcing it when you want to use its functions?

Running a script normally starts a new shell, so functions and variables defined inside it won't be available in your current shell session.

intermediate

How can you check if a function library script was sourced successfully?

After sourcing, try calling a function from the library. If it runs without error, the sourcing worked. You can also check if the function is defined using type function_name.

Which command correctly sources a script named utils.sh?

A bash utils.sh

B ./utils.sh

C run utils.sh

D source utils.sh

The source command runs the script in the current shell, making its functions and variables available.

What is the main benefit of sourcing a function library script?

A It deletes the script after running.

B It runs the script in a new shell.

C It makes functions available in the current shell.

D It compiles the script.

Sourcing runs the script in the current shell, so functions and variables become accessible immediately.

If you run ./library.sh instead of sourcing it, what happens to the functions defined inside?

A They become available in the current shell.

B They are only available in the new shell started by the script.

C They are deleted.

D They run automatically in the current shell.

Running the script starts a new shell, so functions stay local to that shell and do not affect the current one.

Which symbol is a shorthand for the source command in Bash?

A .

B &

C #

D $

The dot . is a shorthand for source in Bash.

How can you verify if a function named greet is defined after sourcing a script?

A type greet

B run greet

C check greet

D find greet

The type command shows if a function or command is defined in the current shell.

Explain what sourcing a script means and why it is useful in Bash scripting.

Think about how sourcing affects your current shell session.

Describe the difference between running a script normally and sourcing it, especially regarding function availability.

Consider where the functions live after each method.

Practice

1. What is the main purpose of using function libraries in bash scripting?

easy

A. To reuse functions across multiple scripts without rewriting code

B. To make scripts run faster by compiling them

C. To encrypt scripts for security

D. To automatically update scripts from the internet

Solution

1. Step 1: Understand function libraries

   Function libraries contain reusable functions that can be shared across scripts.

2. Step 2: Identify the benefit

   Reusing functions avoids rewriting code and keeps scripts clean and maintainable.

3. Final Answer:

   To reuse functions across multiple scripts without rewriting code -> Option A

4. Quick Check:

   Function reuse = To reuse functions across multiple scripts without rewriting code [OK]

Hint: Function libraries let you reuse code easily [OK]

Common Mistakes:

• Thinking libraries speed up script execution
• Confusing libraries with encryption tools
• Assuming libraries auto-update scripts

2. Which of the following is the correct syntax to source a script named lib.sh in bash?

easy

A. load lib.sh

B. import lib.sh

C. source lib.sh

D. include lib.sh

Solution

1. Step 1: Recall bash sourcing commands

   Bash uses source or . to load another script.

2. Step 2: Identify correct syntax

   source lib.sh correctly loads the script named lib.sh.

3. Final Answer:

   source lib.sh -> Option C

4. Quick Check:

   source command = source lib.sh [OK]

Hint: Use 'source' or '.' to load scripts in bash [OK]

Common Mistakes:

• Using 'import' which is not a bash command
• Using 'include' or 'load' which are invalid in bash
• Forgetting to specify the script name

3. Given two files:

lib.sh:
function greet() {
  echo "Hello, $1!"
}

main.sh:
source ./lib.sh
greet "Alice"

What will be the output when running bash main.sh?

medium

A. greet: command not found

B. No output

C. Hello, $1!

D. Hello, Alice!

Solution

1. Step 1: Understand sourcing effect

   The source ./lib.sh command loads the greet function into main.sh.

2. Step 2: Analyze function call

   Calling greet "Alice" runs the function, echoing "Hello, Alice!".

3. Final Answer:

   Hello, Alice! -> Option D

4. Quick Check:

   Function loaded and called = Hello, Alice! [OK]

Hint: Sourcing loads functions so they can be called directly [OK]

Common Mistakes:

• Not sourcing the library before calling the function
• Expecting variable $1 to be literal
• Confusing function definition with execution

4. Consider this script snippet:

source lib.sh
greet "Bob"

But running it gives: main.sh: line 2: greet: command not found
What is the most likely cause?

medium

A. lib.sh does not define the greet function

B. The source command is misspelled

C. The greet function is called before sourcing lib.sh

D. lib.sh has wrong file permissions

Solution

1. Step 1: Check function definition in lib.sh

   If greet is not defined in lib.sh, sourcing won't load it.

2. Step 2: Analyze error message

   "command not found" means the function is missing, not a syntax or permission error.

3. Final Answer:

   lib.sh does not define the greet function -> Option A

4. Quick Check:

   Missing function definition = lib.sh does not define the greet function [OK]

Hint: Check if function exists in sourced file first [OK]

Common Mistakes:

• Assuming source command typo without checking
• Ignoring function order in script
• Not verifying file permissions

5. You want to create a reusable library utils.sh with a function timestamp that prints the current date and time. How should you write and use it in your script run.sh to print the timestamp?

hard

A. In utils.sh: timestamp() { date; } and in run.sh: ./utils.sh; timestamp

B. In utils.sh: timestamp() { echo $(date); } and in run.sh: source utils.sh; timestamp

C. In utils.sh: function timestamp { echo date; } and in run.sh: ./utils.sh; timestamp

D. In utils.sh: timestamp() { date; } and in run.sh: bash utils.sh; timestamp

Solution

1. Step 1: Define timestamp function correctly

   Use timestamp() { echo $(date); } to print current date and time.

2. Step 2: Source utils.sh in run.sh and call function

   Use source utils.sh to load the function, then call timestamp.

3. Final Answer:

   In utils.sh: timestamp() { echo $(date); } and in run.sh: source utils.sh; timestamp -> Option B

4. Quick Check:

   Correct function and sourcing = In utils.sh: timestamp() { echo $(date); } and in run.sh: source utils.sh; timestamp [OK]

Hint: Use echo $(date) inside function and source before calling [OK]

Common Mistakes:

• Running utils.sh instead of sourcing it
• Using echo date instead of echo $(date)
• Calling function without sourcing library