grep -r for recursive search in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to search recursively for the word 'error' in all files.

Linux CLI

grep [1] error *

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

A-i

B-n

C-v

D-r

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-i' which ignores case but does not search recursively.

Using '-v' which inverts the match.

Using '-n' which shows line numbers but not recursive search.

The '-r' option tells grep to search recursively through directories.

2fill in blank

medium

Complete the code to recursively search for 'TODO' in the current directory and all subdirectories.

Linux CLI

grep [1] TODO .

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

A-l

B-r

C-c

D-q

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-l' which lists filenames but does not search recursively.

Using '-c' which counts matches but does not search recursively.

Using '-q' which suppresses output.

The '-r' option makes grep search recursively in the current directory '.' and its subdirectories.

3fill in blank

hard

Fix the error in the command to recursively search for 'main' ignoring case.

Linux CLI

grep -r [1] main ./src

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

A-n

B-v

C-i

D-c

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-v' which inverts the match.

Using '-n' which shows line numbers but does not ignore case.

Using '-c' which counts matches but does not ignore case.

The '-i' option makes grep ignore case when searching.

4fill in blank

hard

Fill both blanks to recursively search for 'config' and show line numbers.

Linux CLI

grep [1] [2] config /etc

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 inverts matches instead of showing line numbers.

Using '-i' which ignores case but does not show line numbers.

Use '-r' for recursive search and '-n' to show line numbers of matches.

5fill in blank

hard

Fill all three blanks to recursively search for 'error' ignoring case and show filenames only.

Linux CLI

grep [1] [2] [3] error /var/log

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

A-r

B-i

C-l

D-n

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-n' which shows line numbers instead of filenames.

Mixing up the order of options but order does not affect grep.

Use '-r' for recursive, '-i' to ignore case, and '-l' to list filenames with matches.

Practice

1. What does the command grep -r 'error' /var/log do?

easy

A. Searches recursively for the word 'error' inside all files in /var/log and its subfolders.

B. Searches only the /var/log folder for files named 'error'.

C. Deletes all files containing the word 'error' in /var/log.

D. Lists all files in /var/log that have the word 'error' in their name.

Solution

1. Step 1: Understand the grep -r option

   The -r flag tells grep to search recursively inside all files in the given directory and its subdirectories.

2. Step 2: Analyze the command arguments

   The command searches for the text 'error' inside all files under the /var/log directory and its subfolders.

3. Final Answer:

   Searches recursively for the word 'error' inside all files in /var/log and its subfolders. -> Option A

4. Quick Check:

   grep -r means recursive search [OK]

Hint: Remember: -r means search inside folders and subfolders [OK]

Common Mistakes:

• Thinking -r searches only filenames, not file contents
• Confusing grep with delete or list commands
• Ignoring the folder path argument

2. Which of the following is the correct syntax to recursively search for the word 'config' in the current directory?

easy

A. grep . -r config

B. grep config -r .

C. grep -r . config

D. grep -r config .

Solution

1. Step 1: Recall grep syntax

   The correct syntax is grep [options] pattern path. The -r option comes before the pattern.

2. Step 2: Match the correct order

   grep -r config . uses grep -r config . which means search recursively for 'config' in current directory ('.').

3. Final Answer:

   grep -r config . -> Option D

4. Quick Check:

   Options order: grep -r pattern path [OK]

Hint: Options come before pattern and path in grep command [OK]

Common Mistakes:

• Placing -r after the pattern or path
• Swapping pattern and path arguments
• Using dot (.) in wrong position

3. Given this folder structure and files:

./docs/readme.txt (contains 'install')
./src/app.py (contains 'install')
./src/utils.py (no 'install')

What is the output of grep -r 'install' ./?

medium

A. ./docs/readme.txt:install
./src/app.py:install

B. ./docs/readme.txt:install

C. ./src/utils.py:install

D. No output

Solution

1. Step 1: Understand recursive search

   The command searches all files under current folder (./) and subfolders for the word 'install'.

2. Step 2: Identify matching files

   Both readme.txt and app.py contain 'install', so their lines are printed with filenames.

3. Final Answer:

   ./docs/readme.txt:install ./src/app.py:install -> Option A

4. Quick Check:

   grep -r finds all matching lines with filenames [OK]

Hint: grep -r shows filename:line for all matches [OK]

Common Mistakes:

• Expecting only filenames without matching lines
• Assuming files without the word appear in output
• Ignoring recursive search in subfolders

4. You run grep 'TODO' /project but get an error: grep: /project: Is a directory. What is the likely cause?

medium

A. You forgot to add the -r option for recursive search.

B. You used the wrong quotes around TODO.

C. You used grep without the -r option but gave a directory path.

D. You ran grep without specifying the directory path.

Solution

1. Step 1: Analyze the error message

   The error says grep treats /project as a file, but it is a directory.

2. Step 2: Understand grep behavior

   Without -r, grep cannot search inside directories and errors out when given a directory path.

3. Final Answer:

   You used grep without the -r option but gave a directory path. -> Option C

4. Quick Check:

   grep needs -r to search directories [OK]

Hint: Use -r to avoid directory errors when searching folders [OK]

Common Mistakes:

• Assuming quotes cause the error
• Thinking -r was forgotten when it was used
• Not specifying directory path at all

5. You want to find all files under /home/user/projects containing the word 'fixme' but exclude any files in node_modules subfolders. Which command achieves this?

hard

A. grep -r 'fixme' /home/user/projects | grep -v node_modules

B. grep -r --exclude-dir=node_modules 'fixme' /home/user/projects

C. grep -r --exclude='node_modules' 'fixme' /home/user/projects

D. grep -r --exclude-dir='fixme' /home/user/projects

Solution

1. Step 1: Understand the requirement

   You want recursive search for 'fixme' but skip directories named 'node_modules'.

2. Step 2: Use correct grep option to exclude directories

   The --exclude-dir=node_modules option tells grep to skip those folders during recursive search.

3. Step 3: Check other options

   grep -r 'fixme' /home/user/projects | grep -v node_modules filters output but still searches inside node_modules, which is inefficient. grep -r --exclude='node_modules' 'fixme' /home/user/projects excludes files named 'node_modules' not directories. grep -r --exclude-dir='fixme' /home/user/projects excludes directories named 'fixme' which is wrong.

4. Final Answer:

   grep -r --exclude-dir=node_modules 'fixme' /home/user/projects -> Option B

5. Quick Check:

   Use --exclude-dir to skip folders in recursive grep [OK]

Hint: Use --exclude-dir to skip folders during recursive grep [OK]

Common Mistakes:

• Using --exclude instead of --exclude-dir for directories
• Filtering output instead of excluding directories
• Wrong option names or misplaced quotes