wc (word, line, character count) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the wc command do in Linux?

The wc command counts the number of lines, words, and bytes in a file or input.

beginner

How do you use wc to count only the number of lines in a file named file.txt?

Use wc -l file.txt. The -l option tells wc to count lines only.

beginner

What option do you use with wc to count only words?

Use the -w option. For example, wc -w file.txt counts words only.

beginner

How can you count characters (including spaces) in a file using wc?

Use the -m option. For example, wc -m file.txt counts characters.

beginner

What output do you get when you run echo "Hello world" | wc?

You get three numbers: lines, words, and bytes. For echo "Hello world", output is 1 2 12 meaning 1 line, 2 words, 12 bytes (including newline).

Which wc option counts only words?

A -l

B -m

C -w

D -c

The -w option counts words only.

What does wc -l file.txt show?

A Number of lines in file.txt

B Number of words in file.txt

C Number of characters in file.txt

D File size in bytes

-l counts lines only.

How do you count characters including spaces with wc?

A -l

B -w

C -s

D -m

-m counts characters including spaces.

What does wc file.txt output by default?

A Lines, words, and bytes counts

B Only lines count

C Only words count

D Only characters count

Without options, wc shows lines, words, and bytes.

What is the output of echo "Hi" | wc -w?

A 2

B 1

C 3

D 0

The echo outputs one word "Hi", so wc -w counts 1.

Explain how to use the wc command to count lines, words, and characters in a file.

Think about what each option counts and how to run wc on a file.

Describe what output you get when running wc without any options on a text input.

Remember the default order: lines, words, bytes.

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