How to Search Files for Text with the Linux grep Command

Published 2026-08-05 · Learn Linux

The grep command finds lines that contain a pattern. Give it a search term and a file, and it prints every matching line: grep error app.log. You can also pipe the output of any command into grep to filter it. This guide covers the options you will use most.

The basic grep syntax

The first argument is the text to find, the rest are files to search. grep prints the file name when you search several files at once.

$ grep error app.log

$ grep error *.log

Ignore case with -i

Searches are case-sensitive by default, so Error and ERROR do not match error. Add -i to find all of them at once.

$ grep -i error app.log

Search recursively with -r

To search a whole directory tree, use -r. It descends into subdirectories and is the command most people use to find where a setting or function appears in a project.

$ grep -r ListenPort /etc

Show line numbers and whole words

Line numbers make results easy to jump to in an editor. Combine them with -w to match a whole word, so cat does not match catalog.

$ grep -n exception app.log

$ grep -wn cat words.txt

Count matches and filter command output

Use -c to count matching lines instead of printing them. grep becomes even more useful when you pipe command output into it with pipes.

$ grep -c error app.log

$ ps aux | grep nginx

For more precise matching, grep understands regular expressions. See the grep reference for the full option list.