Configuration file reading in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Reading a simple config file with key-value pairs

Given a config file settings.conf with the content:

username=admin
password=secret
port=8080

What is the output of this script?

while IFS='=' read -r key value; do
  echo "$key -> $value"
done < settings.conf

Bash Scripting

while IFS='=' read -r key value; do
  echo "$key -> $value"
done < settings.conf

A

username -> admin
password -> secret
port -> 8080

B

username
admin
password
secret
port
8080

C

username=admin
password=secret
port=8080

D SyntaxError: invalid syntax

💡 Hint

Think about how the read command splits lines using the IFS variable.

The script reads each line splitting at '=' into key and value, then prints them with an arrow.

💻 Command Output

intermediate

Ignoring comments and blank lines in config file

Consider a config file app.conf with:

# This is a comment
host=localhost

# Another comment
port=3306

What does this script output?

grep -v '^#' app.conf | grep -v '^$' | while IFS='=' read -r key value; do
  echo "$key=$value"
done

Bash Scripting

grep -v '^#' app.conf | grep -v '^$' | while IFS='=' read -r key value; do
  echo "$key=$value"
done

A

host=localhost
port=3306

B

# This is a comment
host=localhost

# Another comment
port=3306

C

host
localhost
port
3306

D Error: command not found

💡 Hint

grep -v '^#' removes comment lines, grep -v '^$' removes blank lines.

The script filters out comments and blank lines, then reads key-value pairs and prints them.

📝 Syntax

advanced

Parsing config with spaces around equals sign

Which script correctly reads a config file where lines may have spaces around '=' like:

user = admin
password = secret

and prints key and value?

A while IFS='=' read key value; do echo "$key -> $value"; done < config.txt

B while IFS='=' read -r key value; do echo "$key -> $value"; done < config.txt

C while IFS=' = ' read -r key value; do echo "$key -> $value"; done < config.txt

D while read -r line; do key=${line%%=*}; value=${line#*=}; echo "$key -> $value"; done < config.txt

💡 Hint

Think about how to trim spaces around keys and values.

Option D uses string manipulation to split at '=' and preserves spaces to trim later if needed.

🔧 Debug

advanced

Why does this config reading script fail?

This script tries to read config.cfg and print keys and values:

while IFS='=' read -r key value
 do
  echo "$key: $value"
done < config.cfg

But it prints nothing. What is the problem?

Bash Scripting

while IFS='=' read -r key value
 do
  echo "$key: $value"
done < config.cfg

A File config.cfg is empty

B Missing semicolon or newline after read command causes syntax error

C IFS should be set to ':=' instead of '='

D read command needs -a option to read arrays

💡 Hint

Check the syntax of the while loop and read command carefully.

The read command line must end with a semicolon or newline before 'do'. Without it, the shell does not parse the loop correctly.

🚀 Application

expert

Extracting config values into variables

Given a config file settings.ini with:

host=127.0.0.1
port=8080
user=guest

Which script correctly reads these values and sets bash variables host, port, and user accordingly?

A while IFS='=' read -r key value; do declare "$key=$value"; done < settings.ini

B source settings.ini

C while IFS='=' read -r key value; do export $key=$value; done < settings.ini

D eval $(sed 's/^/export /' settings.ini)

💡 Hint

Think about how to safely assign variables from a file in bash.

Option C reads each line, splits key and value, and exports them as variables. Option C fails because the file is not a valid bash script (no spaces allowed). Option C declares variables but does not export them. Option C uses eval which can be unsafe.

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