Function libraries (sourcing scripts) in Bash Scripting - Mini Project: Build & Apply

Using Function Libraries by Sourcing Scripts in Bash

📖 Scenario: You are working on a bash script project where you want to reuse some useful functions stored in a separate file. This helps keep your scripts clean and organized, just like having a toolbox with tools ready to use.

🎯 Goal: Learn how to create a bash function library in one script file and then use source to include those functions in another script. Finally, call the functions to see their output.

📋 What You'll Learn

Create a bash script file named functions.sh with two simple functions.

Create a main bash script named main.sh that sources functions.sh.

Call the sourced functions from main.sh and print their outputs.

💡 Why This Matters

🌍 Real World

In real projects, you often keep reusable bash functions in separate files. This helps you avoid rewriting code and keeps your scripts clean.

💼 Career

Knowing how to source scripts and use function libraries is important for system administrators, DevOps engineers, and anyone automating tasks with bash.

1

Create the function library script

Create a bash script file named functions.sh that defines two functions: greet which prints "Hello, friend!" and farewell which prints "Goodbye, friend!". Write the exact function definitions with these names and messages.

Bash Scripting

# Define the greet and farewell functions here
# Your code here

Hint

Use the syntax function_name() { commands } to define functions in bash.

2

Create the main script and source the function library

Create a bash script file named main.sh. Inside it, use source ./functions.sh to include the functions from functions.sh. This will let you use the functions defined there.

Bash Scripting

# Source the functions.sh file here
# Your code here

Hint

Use source ./functions.sh or . ./functions.sh to include the functions.

3

Call the sourced functions in the main script

In main.sh, after sourcing functions.sh, call the functions greet and farewell by writing their names on separate lines.

Bash Scripting

source ./functions.sh

# Call greet and farewell functions below
# Your code here

Hint

Simply write the function names greet and farewell on separate lines to call them.

4

Run the main script and see the output

Run the main.sh script in your terminal. It should print the greeting and farewell messages from the sourced functions. Write a bash main.sh command and observe the output.

Bash Scripting

# Run the script in terminal and observe output
# Your code here

Hint

Use the command bash main.sh in your terminal to run the script.

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