grep (search text patterns) in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to search for the word 'error' in the file 'log.txt'.

Linux CLI

grep [1] log.txt

Drag options to blanks, or click blank then click option'

A-v

B-i

C"error"

D-r

Attempts:

3 left

💡 Hint

Common Mistakes

Using options like -i or -v instead of the search pattern.

Forgetting to put the search word in quotes.

The correct syntax to search for the word 'error' is to put it in quotes after grep.

2fill in blank

medium

Complete the code to search for the word 'Warning' in 'system.log' ignoring case.

Linux CLI

grep [1] "Warning" system.log

Drag options to blanks, or click blank then click option'

A-v

B-i

C-r

D-c

Attempts:

3 left

💡 Hint

Common Mistakes

Using -v which inverts the match.

Using -r which searches recursively.

The -i option makes grep ignore case when searching.

3fill in blank

hard

Fix the error in the command to count lines containing 'fail' in 'report.txt'.

Linux CLI

grep [1] fail report.txt

Drag options to blanks, or click blank then click option'

A-c

B-i

C-v

D-n

Attempts:

3 left

💡 Hint

Common Mistakes

Using -i which ignores case but does not count.

Using -v which inverts the match.

The -c option counts the number of matching lines.

4fill in blank

hard

Fill both blanks to search recursively for 'TODO' in all files and show line numbers.

Linux CLI

grep [1] [2] TODO .

Drag options to blanks, or click blank then click option'

A-r

B-i

C-n

D-v

Attempts:

3 left

💡 Hint

Common Mistakes

Using -v which excludes matches.

Using -i which ignores case but is not needed here.

Use -r to search recursively and -n to show line numbers.

5fill in blank

hard

Fill all three blanks to search case-insensitively for 'error', count matches, and show filenames only.

Linux CLI

grep [1] [2] [3] error /var/logs/*.log

Drag options to blanks, or click blank then click option'

A-i

B-c

C-l

D-n

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up -c and -l options.

Forgetting to use -i for case-insensitive search.

Use -i for case-insensitive, -c to count matches, and -l to show filenames only.

Practice

1. What does the grep command do in Linux?

easy

A. Searches text for lines matching a pattern

B. Deletes files matching a pattern

C. Copies files to another directory

D. Lists all files in a directory

Solution

1. Step 1: Understand the purpose of grep

   The grep command is used to search text for lines that match a given pattern.

2. Step 2: Compare options

   Options B, C, and D describe other commands like rm, cp, and ls, not grep.

3. Final Answer:

   Searches text for lines matching a pattern -> Option A

4. Quick Check:

   grep = search text lines [OK]

Hint: grep finds lines with your pattern in text [OK]

Common Mistakes:

• Confusing grep with file commands like rm or cp
• Thinking grep modifies files instead of searching
• Assuming grep lists files instead of searching content

2. Which of the following is the correct syntax to search for the word error in a file named log.txt using grep?

easy

A. grep log.txt error

B. grep -f error log.txt

C. grep error log.txt

D. grep -e log.txt error

Solution

1. Step 1: Recall grep syntax

   The basic syntax is grep [pattern] [file]. So to search for 'error' in 'log.txt', use grep error log.txt.

2. Step 2: Analyze other options

   grep -f error log.txt uses -f which expects a file of patterns, not a pattern string. Options C and D have arguments reversed or incorrect flags.

3. Final Answer:

   grep error log.txt -> Option C

4. Quick Check:

   grep pattern file = grep error log.txt [OK]

Hint: Use grep pattern filename order to avoid errors [OK]

Common Mistakes:

• Swapping pattern and filename positions
• Using -f flag incorrectly for pattern string
• Confusing -e flag usage

3. Given a file data.txt with the following content:

apple
banana
Apple
BANANA
apple pie
banana split

What is the output of the command grep -i 'apple' data.txt?

medium

A. apple
apple pie

B. Apple
BANANA
banana split

C. apple pie
banana split

D. apple
Apple
apple pie

Solution

1. Step 1: Understand -i option

   The -i option makes grep case-insensitive, so it matches 'apple' and 'Apple'.

2. Step 2: Identify matching lines

   Lines containing 'apple' ignoring case are: 'apple', 'Apple', and 'apple pie'.

3. Final Answer:

   apple Apple apple pie -> Option D

4. Quick Check:

   grep -i matches apple and Apple [OK]

Hint: Use -i to ignore case when searching text [OK]

Common Mistakes:

• Ignoring case sensitivity without -i
• Missing lines with partial matches like 'apple pie'
• Confusing output order

4. You run the command grep -c 'fail' report.txt but it returns 0 even though you know the file contains the word 'fail'. What is the most likely reason?

medium

A. The file report.txt is empty

B. The word 'fail' is in uppercase like 'FAIL' and grep is case-sensitive by default

C. The grep command syntax is incorrect

D. The file report.txt does not exist

Solution

1. Step 1: Understand grep -c behavior

   The -c option counts matching lines. If it returns 0, no exact matches were found.

2. Step 2: Consider case sensitivity

   By default, grep is case-sensitive. If the file has 'FAIL' but you search 'fail', it won't match.

3. Final Answer:

   The word 'fail' is in uppercase like 'FAIL' and grep is case-sensitive by default -> Option B

4. Quick Check:

   grep is case-sensitive unless -i used [OK]

Hint: Use -i to ignore case if matches return zero [OK]

Common Mistakes:

• Assuming grep ignores case by default
• Not checking file content carefully
• Mistaking syntax errors for no matches

5. You want to find how many lines in server.log contain the word timeout ignoring case, and display only the count. Which command should you use?

hard

A. grep -i -c timeout server.log

B. grep -i timeout server.log

C. grep timeout -i -c server.log

D. grep -c timeout server.log

Solution

1. Step 1: Identify options needed

   You need to ignore case (-i) and count matching lines (-c).

2. Step 2: Check correct option order

   Options can be combined as -i -c or -c -i. grep -i -c timeout server.log uses both correctly before pattern and file.

3. Step 3: Analyze other options

   grep -c timeout server.log lacks case insensitivity. grep -i timeout server.log shows matches but not count. grep timeout -i -c server.log has incorrect argument order (pattern before options).

4. Final Answer:

   grep -i -c timeout server.log -> Option A

5. Quick Check:

   Use -i and -c together for case-insensitive count [OK]

Hint: Combine -i and -c to count ignoring case [OK]

Common Mistakes:

• Omitting -i for case-insensitive search
• Using pattern before options causing errors
• Expecting output lines instead of count