Welcome to Linux: The grep Command

Among the oldest and most thoroughly tested of these tools is grep, a pattern-matching search utility that has been described as "a small program that does one thing well." That description remains just as accurate today as it was more than fifty years ago. This module walks through grep from first principles — basic pattern matching, filtering real-world log files, combining grep with other commands in a pipeline, and using both basic and extended regular expressions to build precise, powerful search patterns.

Because Linux relies so heavily on plain text for configuration, logging, and metadata, administrators are constantly working with text that is either sitting in files or moving between programs as text streams. Manually reading through this text is impractical — a single system log file can easily contain 50,000 lines and more than 10 million characters. Purpose-built filtering tools make it possible to extract only the information that matters from data at that scale.