head and tail in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the head command do in Linux?

The head command shows the first few lines of a file or input. By default, it shows the first 10 lines.

beginner

How do you use tail to see the last 5 lines of a file named log.txt?

Use tail -n 5 log.txt. This shows the last 5 lines of the file log.txt.

beginner

What option do you use with head or tail to specify the number of lines?

Use the -n option followed by the number of lines you want to see. For example, head -n 3 file.txt shows the first 3 lines.

intermediate

How can tail be used to watch a file as it grows?

Use tail -f filename. This shows the last lines and keeps updating the output as new lines are added, like watching a live log.

beginner

If you want to see the first 20 lines of a file, which command would you use?

You would use head -n 20 filename to see the first 20 lines of the file.

What is the default number of lines shown by the head command?

A 10

B 5

C 20

D 15

By default, head shows the first 10 lines of a file or input.

Which command shows the last 15 lines of a file named data.txt?

A head -n 15 data.txt

B tail -15 data.txt

C head -15 data.txt

D tail -n 15 data.txt

Use tail -n 15 data.txt to see the last 15 lines.

How do you continuously monitor new lines added to a file server.log?

A head -f server.log

B head -n server.log

C tail -f server.log

D tail -n server.log

tail -f server.log shows the last lines and updates as new lines are added.

What does head -n 0 file.txt display?

A No lines

B The first line

C The entire file

D The last line

Using -n 0 means show zero lines, so no output is shown.

Which command shows the first 10 lines of standard input?

A tail

B head

C head -n 20

D tail -n 10

Running head without a file reads from standard input and shows the first 10 lines by default.

Explain how you would use head and tail to view parts of a file.

Think about how you check the start or end of a long list or log.

Describe a real-life situation where tail -f would be useful.

Imagine you are watching a live scoreboard or chat messages.

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