Linux grep Command Examples

Practical grep snippets for searching text, filtering logs, and finding patterns in files.

Linux grep CLI

Basic Search

Search for a string in a file

grep "search_term" filename.txt

Basic grep usage. Returns all lines containing the search term.

Case-insensitive search

grep -i "search_term" filename.txt

Use -i to ignore case. Matches "Error", "error", "ERROR" etc.

Search recursively in directory

grep -r "search_term" /path/to/dir/

Use -r to search all files in a directory recursively.

Filter & Count

Count matching lines

grep -c "search_term" filename.txt

Returns the number of lines that match instead of the lines themselves.

Show line numbers

grep -n "search_term" filename.txt

Use -n to display line numbers alongside matching lines.

Invert match (exclude lines)

grep -v "search_term" filename.txt

Use -v to show lines that do NOT match the pattern.

Log Filtering

Filter ERROR logs

grep "ERROR" /var/log/app.log

Common use case: extract error lines from application logs.

Filter logs with context lines

grep -A 3 -B 3 "ERROR" /var/log/app.log

-A 3 shows 3 lines after the match. -B 3 shows 3 lines before. Useful for debugging.

Tail log and grep in real-time

tail -f /var/log/app.log | grep "ERROR"

Monitor a log file in real-time and filter for errors. Useful for live debugging.

Advanced Usage

Search with regex

grep -E "error|warn|fatal" filename.txt

Use -E for extended regex. This example matches lines with "error", "warn", or "fatal".

Search only filenames

grep -rl "search_term" /path/to/dir/

Use -l to list only filenames that contain the match, not the lines.

Exclude specific file types

grep -r "search_term" /path/ --exclude="*.log"

Exclude files matching a pattern. Use --include to do the opposite.