head and tail in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of head command with line count

What is the output of the command head -n 3 sample.txt if sample.txt contains these lines?

Line1
Line2
Line3
Line4
Line5

Linux CLI

head -n 3 sample.txt

A

Line4
Line5

B

Line3
Line4
Line5

C

Line1
Line2
Line3
Line4
Line5

D

Line1
Line2
Line3

💡 Hint

head shows the first lines of a file.

The head -n 3 command prints the first 3 lines of the file.

💻 Command Output

intermediate

Output of tail command with byte count

What is the output of tail -c 5 sample.txt if sample.txt contains exactly HelloWorld?

Linux CLI

tail -c 5 sample.txt

A HelloWorld

B Hello

C World

D dlroW

💡 Hint

tail -c shows last bytes, counting characters.

The last 5 characters of 'HelloWorld' are 'World'.

🔧 Debug

advanced

Effect of tail -n with negative number

You run tail -n -3 sample.txt. What happens?
Choose the correct statement.

Linux CLI

tail -n -3 sample.txt

A The command syntax is correct; no error should occur.

B Negative numbers are not allowed with -n option in tail.

C The -n option requires a positive integer or zero.

D The file sample.txt does not exist.

💡 Hint

Check tail manual for allowed values of -n. Negative numbers indicate 'all but last N lines'.

The command syntax is incorrect; tail does not accept negative numbers with -n option. It will produce an error.

🧠 Conceptual

advanced

Combining head and tail to get middle lines

You want to extract lines 4 to 6 from a file named data.txt. Which command correctly does this?

A head -n 6 data.txt | tail -n 3

B tail -n 6 data.txt | head -n 3

C tail -n 3 data.txt | head -n 6

D head -n 3 data.txt | tail -n 6

💡 Hint

Use head to get first 6 lines, then tail to get last 3 of those.

head -n 6 gets first 6 lines; tail -n 3 extracts lines 4,5,6 from those.

🚀 Application

expert

Script to monitor last 10 lines of a growing log file

You want to write a script that continuously shows the last 10 lines of app.log as it grows, updating in real-time. Which command achieves this?

A tail -f -n 10 app.log

B head -f -n 10 app.log

C tail -n 10 app.log

D head -n 10 app.log

💡 Hint

Use tail with follow option to watch file growth.

tail -f -n 10 shows last 10 lines and updates as file grows.

Practice

1. What does the head command do by default when run on a text file?

easy

A. Counts the number of lines in the file

B. Shows the last 10 lines of the file

C. Deletes the first 10 lines of the file

D. Shows the first 10 lines of the file

Solution

1. Step 1: Understand the default behavior of head

   The head command shows the start of a file, by default 10 lines.

2. Step 2: Compare with other options

   tail shows the end, but head shows the beginning lines.

3. Final Answer:

   Shows the first 10 lines of the file -> Option D

4. Quick Check:

   head = first 10 lines [OK]

Hint: Remember: head = start, tail = end of file [OK]

Common Mistakes:

• Confusing head with tail
• Thinking head deletes lines
• Assuming head counts lines

2. Which of the following is the correct syntax to display the last 5 lines of a file named log.txt?

easy

A. tail -n 5 log.txt

B. head -n 5 log.txt

C. tail 5 log.txt

D. head 5 log.txt

Solution

1. Step 1: Identify the command to show last lines

   tail shows the end of a file, so it is used to show last lines.

2. Step 2: Use correct syntax with -n option

   The option -n 5 specifies to show 5 lines. So tail -n 5 log.txt is correct.

3. Final Answer:

   tail -n 5 log.txt -> Option A

4. Quick Check:

   tail -n 5 shows last 5 lines [OK]

Hint: Use -n with tail to specify number of lines [OK]

Common Mistakes:

• Using head instead of tail
• Omitting -n option
• Using tail without -n for line count

3. Given a file data.txt with 20 lines, what will be the output of head -n 3 data.txt | tail -n 2?

medium

A. Lines 2 and 3 of data.txt

B. Lines 1 and 2 of data.txt

C. Lines 18 and 19 of data.txt

D. Lines 3 and 4 of data.txt

Solution

1. Step 1: Understand head -n 3 data.txt

   This command outputs the first 3 lines: lines 1, 2, and 3.

2. Step 2: Apply tail -n 2 on the output

   tail -n 2 takes the last 2 lines of the previous output, so lines 2 and 3.

3. Final Answer:

   Lines 2 and 3 of data.txt -> Option A

4. Quick Check:

   head 3 then tail 2 = lines 2 & 3 [OK]

Hint: Pipe head then tail to slice lines from start [OK]

Common Mistakes:

• Assuming tail works on whole file, not head output
• Confusing line numbers
• Thinking tail -n 2 shows first 2 lines

4. You run head -n 5 file.txt but get an error: head: invalid option -- 'n'. What is the likely cause?

medium

A. The file file.txt does not exist

B. The head command version does not support -n

C. You need to use --lines=5 instead of -n 5

D. You must run the command as root

Solution

1. Step 1: Analyze the error message

   The error says invalid option -- 'n', meaning -n is not recognized.

2. Step 2: Understand command version differences

   Some older or non-GNU versions of head do not support -n and require different syntax.

3. Final Answer:

   The head command version does not support -n -> Option B

4. Quick Check:

   Invalid option error means unsupported flag [OK]

Hint: Check command version if options cause errors [OK]

Common Mistakes:

• Assuming file missing causes option error
• Trying to run as root unnecessarily
• Using wrong syntax without checking version

5. You want to monitor the last 15 lines of a growing log file app.log in real-time but only want to see the newest lines as they appear. Which command combination is best?

hard

A. head -n 15 app.log

B. tail -n 15 app.log

C. tail -n 15 -f app.log

D. head -n 15 -f app.log

Solution

1. Step 1: Understand the need to see last lines and follow updates

   You want the last 15 lines and to watch new lines as they are added.

2. Step 2: Use tail with -n 15 and -f

   tail -n 15 -f app.log shows last 15 lines and follows file changes live.

3. Final Answer:

   tail -n 15 -f app.log -> Option C

4. Quick Check:

   tail -n 15 -f = last 15 lines + live updates [OK]

Hint: Use tail -f to follow file changes live [OK]

Common Mistakes:

• Using head which shows start, not end
• Omitting -f to follow updates
• Using head -f which is invalid