grep -r for recursive search in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this recursive grep command?

You have a directory with two files:

file1.txt contains:
apple
banana
cherry

file2.txt contains:
banana
date
fig

What will be the output of the command grep -r banana . when run inside this directory?

A

banana
banana

B

./file1.txt:banana
./file2.txt:banana

C ./file1.txt:banana

D No output

💡 Hint

Remember that -r searches inside files recursively and shows filename with matching lines.

The -r option makes grep search all files recursively and print matching lines with filenames. Both files contain 'banana', so both lines are shown with filenames.

💻 Command Output

intermediate

What error does this grep command produce?

What error message will this command produce?

grep -r --include='*.txt' 'apple' /nonexistentdir

A grep: invalid option -- 'r'

B No output, command runs silently

C grep: missing argument after '--include='

D grep: /nonexistentdir: No such file or directory

💡 Hint

Check what happens when grep tries to search a directory that does not exist.

The directory /nonexistentdir does not exist, so grep reports 'No such file or directory' error.

📝 Syntax

advanced

Which grep command correctly searches recursively only in .log files?

You want to search for the word 'error' recursively but only inside files ending with .log. Which command does this correctly?

A grep -r error --include='*.log' .

B grep --include='*.log' -r error .

C grep -r --include='*.log' error .

D grep error -r --include='*.log' .

💡 Hint

The order of options matters for some commands; check the grep manual for option placement.

Option C is the standard and recommended way: options first, then pattern, then path. Others may work but can cause unexpected behavior or errors.

🚀 Application

advanced

How to exclude a directory from recursive grep search?

You want to search recursively for 'TODO' but exclude the directory named 'vendor'. Which command achieves this?

A grep -r --exclude-dir=vendor TODO .

B grep -r --exclude=vendor TODO .

C grep -r --exclude-dir='vendor/*' TODO .

D grep -r --exclude-dir vendor TODO .

💡 Hint

Use the option that excludes directories by name, not files.

The option --exclude-dir=vendor excludes the directory named 'vendor' from the recursive search. Option A excludes files named 'vendor', not directories. Option A uses a wrong pattern. Option A misses the equal sign which is required.

🧠 Conceptual

expert

Why does 'grep -r' sometimes show binary file matches and how to avoid it?

When running grep -r 'pattern' ., sometimes grep shows 'Binary file matches' messages instead of matching lines. Why does this happen and how can you make grep show matching lines only for text files?

A Because grep detects binary files and by default only reports matches without content; use <code>grep -r --binary-files=text</code> to force text output.

B Because grep cannot search recursively in binary files; use <code>grep -r --text</code> to fix recursion.

C Because grep treats all files as binary by default; use <code>grep -r --no-binary</code> to disable binary detection.

D Because grep only searches filenames for binary files; use <code>grep -r --files-with-matches</code> to see lines.

💡 Hint

Check grep's handling of binary files and the option to treat binary files as text.

Grep detects binary files and by default shows 'Binary file matches' without printing matching lines. Using --binary-files=text forces grep to treat binary files as text and print matching lines.