Grep With Flags

grep becomes even more powerful when you add flags to control how it searches and what it displays.

Most useful grep flags:

-i — case insensitive search. Matches regardless of uppercase or lowercase:

grep -i "error" server.log   # matches error, Error, ERROR

-n — show line numbers alongside each matching line:

grep -n "error" server.log
3:error: disk full
6:error: connection timeout

-c — show only the count of matching lines, not the lines themselves:

grep -c "error" server.log
2

-v — invert the search — show lines that do not match the pattern:

grep -v "info" server.log
error: disk full
warning: high memory usage
error: connection timeout

-r — search recursively through all files in a directory:

grep -r "error" logs/   # search all files inside the logs folder

-l — show only the filenames that contain a match, not the matching lines:

grep -l "error" *.log

Combining flags:

You can combine multiple flags together:

grep -in "error" server.log   # case insensitive + show line numbers
grep -vc "info" server.log    # invert + count non-info lines