Configuration file reading in Bash Scripting - Mini Project: Build & Apply

Configuration file reading

📖 Scenario: You are managing a simple script that needs to read settings from a configuration file to decide how it behaves.Imagine you have a config file that stores user preferences like username and theme color.

🎯 Goal: Build a bash script that reads a configuration file and extracts specific settings into variables.This will help automate tasks based on user preferences stored in the config file.

📋 What You'll Learn

Create a configuration file named settings.conf with exact key-value pairs.

Write a bash script that reads the configuration file line by line.

Extract the values of username and theme from the config file.

Print the extracted values in a friendly message.

💡 Why This Matters

🌍 Real World

Many scripts and programs use configuration files to store user preferences or settings. Reading these files allows automation scripts to adapt their behavior without changing code.

💼 Career

Understanding how to read config files is essential for system administrators, DevOps engineers, and anyone writing automation scripts to manage software or servers.

1

Create the configuration file

Create a file named settings.conf with these exact lines:
username=alice
theme=dark

Bash Scripting

# Create the file settings.conf with the required lines
# Your code here

Hint

Use echo commands with redirection to create the file and add lines.

2

Prepare variables to hold config values

In your bash script, create two empty variables called username and theme to hold the config values.

Bash Scripting

echo "username=alice" > settings.conf
echo "theme=dark" >> settings.conf

# Create empty variables username and theme
# Your code here

Hint

Assign empty strings to username and theme variables.

3

Read the configuration file and extract values

Use a while loop with read to read settings.conf line by line.
Inside the loop, use case to check if the line starts with username= or theme=.
Extract the value after the equal sign and assign it to the corresponding variable.

Bash Scripting

echo "username=alice" > settings.conf
echo "theme=dark" >> settings.conf

username=""
theme=""

# Read settings.conf line by line and extract username and theme
# Your code here

Hint

Use parameter expansion ${line#username=} to get the value after the equal sign.

4

Print the extracted configuration values

Print the message: User: alice, Theme: dark using the variables username and theme with echo and an f-string style format.

Bash Scripting

echo "username=alice" > settings.conf
echo "theme=dark" >> settings.conf

username=""
theme=""

while IFS= read -r line; do
  case "$line" in
    username=*) username="${line#username=}" ;; 
    theme=*) theme="${line#theme=}" ;; 
  esac
done < settings.conf

# Print the message with username and theme
# Your code here

Hint

Use printf with %s placeholders to insert variables.

Practice

1. What is the main purpose of reading a configuration file in a bash script?

easy

A. To load variable values that the script can use

B. To execute commands from the internet

C. To delete files automatically

D. To compile the script into a binary

Solution

1. Step 1: Understand configuration files

   Configuration files usually contain variable assignments that scripts read to get settings.

2. Step 2: Purpose of reading config files

   Reading these files allows scripts to use flexible values without hardcoding them.

3. Final Answer:

   To load variable values that the script can use -> Option A

4. Quick Check:

   Config files provide variables = B [OK]

Hint: Config files store variables for scripts to use [OK]

Common Mistakes:

• Thinking config files run commands directly
• Confusing config files with executable scripts
• Assuming config files delete or compile code

2. Which of the following is the correct syntax to read a config file named settings.conf in a bash script?

easy

A. source settings.conf

B. read settings.conf

C. import settings.conf

D. execute settings.conf

Solution

1. Step 1: Identify the command to read config files

   In bash, source or . is used to read and execute commands from a file in the current shell.

2. Step 2: Check options

   read reads input, import is not a bash command, and execute is invalid.

3. Final Answer:

   source settings.conf -> Option A

4. Quick Check:

   Use source or . to read config [OK]

Hint: Use 'source' or '.' to load config files [OK]

Common Mistakes:

• Using 'read' command instead of 'source'
• Trying to 'import' like in other languages
• Assuming 'execute' runs the config file

3. Given the config file app.conf with content:

USERNAME=guest
PORT=8080

What will the output of this script be?

source app.conf
echo "User: $USERNAME, Port: $PORT"

medium

A. User: $USERNAME, Port: $PORT

B. User: , Port:

C. Syntax error

D. User: guest, Port: 8080

Solution

1. Step 1: Source the config file

   The source app.conf command loads variables USERNAME and PORT into the script.

2. Step 2: Print the variables

   The echo command prints the values of USERNAME and PORT, which are 'guest' and '8080'.

3. Final Answer:

   User: guest, Port: 8080 -> Option D

4. Quick Check:

   Variables loaded and printed = C [OK]

Hint: Sourcing sets variables, echo prints their values [OK]

Common Mistakes:

• Not sourcing the file before using variables
• Expecting variable names printed literally
• Confusing syntax causing errors

4. What is wrong with this script snippet that tries to read config.cfg and print a variable?

source config.cfg
echo "Value: $VALUE"

Assuming config.cfg contains VALUE=42, but the output is empty.

medium

A. The script forgot to use 'export' before sourcing

B. The config file has spaces around '=' causing no assignment

C. The variable name is case-sensitive and mismatched

D. The source command is misspelled

Solution

1. Step 1: Check config file syntax

   If the config file has spaces like VALUE = 42, bash treats it as a command, not assignment.

2. Step 2: Effect on sourcing

   Because of wrong syntax, VALUE is not set, so echo prints empty.

3. Final Answer:

   The config file has spaces around '=' causing no assignment -> Option B

4. Quick Check:

   No spaces in var assignment = A [OK]

Hint: No spaces around '=' in config files [OK]

Common Mistakes:

• Adding spaces around '=' in variable assignments
• Thinking 'export' is needed before sourcing
• Ignoring case sensitivity of variable names

5. You want to safely read a config file settings.conf that might contain unsafe commands. Which approach is best to avoid running unwanted code while still getting variable values?

hard

A. Run the config file as a separate script

B. Use source settings.conf directly without checks

C. Manually parse the file line-by-line to extract variable assignments

D. Delete the config file before sourcing

Solution

1. Step 1: Understand risks of sourcing

   Using source runs all commands in the file, which can be unsafe if file is untrusted.

2. Step 2: Safe alternative

   Manually reading lines and extracting only variable assignments avoids executing harmful commands.

3. Final Answer:

   Manually parse the file line-by-line to extract variable assignments -> Option C

4. Quick Check:

   Parse manually to avoid unsafe code = A [OK]

Hint: Parse config lines manually to avoid running code [OK]

Common Mistakes:

• Sourcing untrusted config files directly
• Running config as a script without validation
• Deleting config file instead of securing it