What command is used for searching through files and returning lines that contain specific patterns?

The command used for searching through files and returning lines that contain specific patterns is "grep." This powerful utility is widely utilized in Linux to search text using regular expressions, enabling users to find specific strings or patterns within files quickly. When executed, grep scans through the content of specified files and outputs lines that match the given pattern, making it an essential tool for text processing and data analysis in the command line environment.

In contrast, locate is designed for finding files by name rather than searching within the file contents, while find is focused on locating files based on specific criteria like name, type, or modification time. Cat, on the other hand, is used for displaying file contents and does not perform any search functions at all. These differences highlight why grep is the appropriate choice for the task at hand.