wc (word, line, character count) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of wc with multiple files

What is the output of the following command if file1.txt contains 3 lines, 10 words, and 50 characters, and file2.txt contains 2 lines, 5 words, and 20 characters?

wc file1.txt file2.txt

Linux CLI

wc file1.txt file2.txt

A

 3 10 50 file1.txt
 2 5 20 file2.txt
 6 15 70 total

B

 3 10 50 file1.txt
 2 5 20 file2.txt
 5 15 70 total

C

 3 10 50 file1.txt
 2 5 20 file2.txt
 5 15 60 total

D

 3 10 50 file1.txt
 2 5 20 file2.txt
 5 15 70 file2.txt

💡 Hint

Remember that wc sums lines, words, and characters for the total line.

The wc command outputs lines, words, and characters for each file, then sums them for the total line. Here, 3+2=5 lines, 10+5=15 words, 50+20=70 characters.

💻 Command Output

intermediate

Counting words only with wc

What is the output of this command if input.txt contains the text "Hello world from Linux CLI"?

wc -w input.txt

Linux CLI

wc -w input.txt

A 4 input.txt

B 6 input.txt

C Error: file not found

D 5 input.txt

💡 Hint

Count the words separated by spaces.

The text has 5 words: Hello, world, from, Linux, CLI. The -w option counts words only.

📝 Syntax

advanced

Correct usage of wc to count lines

Which option correctly counts only the number of lines in file.txt?

A wc -l file.txt

B wc -c file.txt

C wc -w file.txt

D wc --lines file.txt

💡 Hint

The option for lines is a single letter.

The -l option counts lines. -c counts bytes, -w counts words, and --lines is not a valid option.

🔧 Debug

advanced

Identify the error in wc command usage

What error will this command produce?

wc -x file.txt

Linux CLI

wc -x file.txt

A

wc: invalid option -- 'x'
Try 'wc --help' for more information.

B 0 file.txt

C Counts lines, words, and bytes normally

D wc: file.txt: No such file or directory

💡 Hint

Check if -x is a valid wc option.

The -x option is not valid for wc, so it produces an invalid option error.

🚀 Application

expert

Using wc in a script to count total words in multiple files

You want to write a script that sums the total number of words across three files: a.txt, b.txt, and c.txt. Which command will correctly output only the total word count?

A wc -w a.txt b.txt c.txt | grep total | awk '{print $2}'

B wc -w a.txt b.txt c.txt | head -1 | awk '{print $1}'

C wc -w a.txt b.txt c.txt | tail -1 | awk '{print $1}'

D wc -w a.txt b.txt c.txt | awk '{sum += $1} END {print sum}'

💡 Hint

The total line is the last line of wc output when multiple files are given.

When wc -w is run on multiple files, the last line shows the total word count. tail -1 gets that line, and awk '{print $1}' extracts the count.

Practice

1. What does the wc command do in Linux?

easy

A. Counts lines, words, and characters in text

B. Changes file permissions

C. Lists files in a directory

D. Displays disk usage

Solution

1. Step 1: Understand the purpose of wc

   The wc command is used to count lines, words, and characters in text files or input.

2. Step 2: Compare with other commands

   Other options like changing permissions or listing files are done by different commands (chmod, ls), not wc.

3. Final Answer:

   Counts lines, words, and characters in text -> Option A

4. Quick Check:

   wc = counts lines, words, characters [OK]

Hint: Remember: wc = word count tool for text [OK]

Common Mistakes:

• Confusing wc with ls or chmod
• Thinking wc changes files
• Assuming wc shows disk usage

2. Which of the following is the correct syntax to count only the number of lines in a file named file.txt?

easy

A. wc -w file.txt

B. wc -l file.txt

C. wc -c file.txt

D. wc -m file.txt

Solution

1. Step 1: Identify option for line count

   The -l option with wc counts lines in the file.

2. Step 2: Verify other options

   -w counts words, -c counts bytes, and -m counts characters, so they are incorrect for line count.

3. Final Answer:

   wc -l file.txt -> Option B

4. Quick Check:

   -l means lines [OK]

Hint: Use -l to count lines, not -w or -c [OK]

Common Mistakes:

• Using -w or -c instead of -l
• Forgetting the filename
• Mixing up -m and -c options

3. Given a file example.txt containing the text:

Hello world
This is a test

What is the output of wc example.txt?

medium

A. 2 6 27 example.txt

B. 3 5 24 example.txt

C. 2 5 24 example.txt

D. 3 6 25 example.txt

Solution

1. Step 1: Count lines, words, and characters in the file

   Lines: 2 ("Hello world" and "This is a test")
   Words: 6 ("Hello", "world", "This", "is", "a", "test")
   Characters: Count all characters including spaces and newlines.
   "Hello world" = 11 chars, newline = 1, "This is a test" = 14 chars, newline = 1, total = 27 chars.

2. Step 2: Match counts with options

   2 6 27 example.txt matches exactly: 2 lines, 6 words, 27 characters.

3. Final Answer:

   2 6 27 example.txt -> Option A

4. Quick Check:

   Lines=2, Words=6, Characters=27 [OK]

Hint: Count lines, words, chars carefully; wc shows all three by default [OK]

Common Mistakes:

• Miscounting words or lines
• Ignoring newline characters in count
• Assuming output order is different

4. You run wc -l file.txt but get an error: wc: invalid option -- 'x'. What is the likely cause?

medium

A. The file file.txt does not exist

B. You forgot to specify the filename

C. You typed an invalid option like -x by mistake

D. The wc command is not installed

Solution

1. Step 1: Analyze the error message

   The error says "invalid option -- 'x'", meaning wc received an option -x which it does not recognize.

2. Step 2: Identify common causes

   This usually happens if you mistype an option, for example -x instead of -l or -w.

3. Final Answer:

   You typed an invalid option like -x by mistake -> Option C

4. Quick Check:

   Invalid option error means wrong flag [OK]

Hint: Check option spelling carefully if wc shows invalid option error [OK]

Common Mistakes:

• Confusing file not found with invalid option error
• Assuming missing filename causes invalid option error
• Ignoring typo in command options

5. You want to count only the characters (not bytes) in a UTF-8 encoded file data.txt. Which command should you use?

hard

A. wc -c data.txt

B. wc -w data.txt

C. wc -l data.txt

D. wc -m data.txt

Solution

1. Step 1: Understand difference between -c and -m

   -c counts bytes, which may differ from characters in UTF-8 files because some characters use multiple bytes.
   -m counts characters, correctly handling multibyte UTF-8 characters.

2. Step 2: Choose correct option for character count

   To count characters (not bytes), use wc -m.

3. Final Answer:

   wc -m data.txt -> Option D

4. Quick Check:

   -m counts characters, not bytes [OK]

Hint: Use -m for characters, -c counts bytes (important for UTF-8) [OK]

Common Mistakes:

• Using -c and expecting character count
• Confusing words (-w) with characters
• Ignoring UTF-8 multibyte character effects