How to search file contents with grep

1. Searching inside files with grep
2. Search recursively
3. Case-insensitive matching
4. Show line numbers
5. Match whole words and invert
6. Count matches
7. Show surrounding context
8. Using regular expressions
9. Piping into grep

#Searching inside files with grep

While find locates files by their name or metadata, grep searches what's inside them. It scans for lines matching a pattern and prints them. The basic form is grep 'pattern' file:

grep 'database' config/app.php

#Search recursively

To search every file under a directory, add -r (recursive). This is the one I use most:

grep -r 'API_KEY' .

#Case-insensitive matching

By default grep is case-sensitive. Add -i to ignore case, so Error, error and ERROR all match:

grep -ri 'todo' src/

#Show line numbers

Add -n to prefix each match with its line number, which makes jumping to it in an editor much faster:

grep -n 'function' app.js

#Match whole words and invert

Use -w to match a whole word only, so searching log won't also match login or catalog:

grep -w 'log' app.php

Flip the logic with -v to print lines that don't match — useful for filtering noise out of a file:

grep -v '^#' config.ini

That example drops every commented line (those starting with #).

#Count matches

When you only care how many times something appears, -c prints the count of matching lines instead of the lines themselves:

grep -c 'POST' access.log

#Show surrounding context

Sometimes the matching line alone isn't enough. Use -A for lines after, -B for before, and -C for both:

grep -C 3 'Exception' storage/logs/laravel.log

This prints each match with 3 lines on either side.

#Using regular expressions

The pattern is a regular expression, so you can match more than literal text. Add -E for extended regex syntax like alternation and +:

grep -E 'warning|error|critical' app.log

This finds any line containing one of those three words.

#Piping into grep

grep really shines at the end of a pipe, filtering the output of another command. This is everyday glue on the command line:

ps aux | grep nginx
git log --oneline | grep 'fix'

Combine these flags freely — for example grep -rin 'token' . gives you a recursive, case-insensitive search with line numbers — and grep becomes one of the most useful tools in your kit.