What does 'grep' command do?

The 'grep' command is a powerful utility commonly used in Unix/Linux environments that searches through text data for a specific pattern. When you use 'grep', you provide it with a pattern (which can be a string or a regular expression) and one or more files to search. The output will include any lines from those files that match the specified pattern. This makes 'grep' particularly handy for extracting specific information from log files, configuration files, or any text-based data.

For instance, if you wanted to find all occurrences of the word "error" in a log file, you could run a command like grep "error" logfile.txt, and it would display all the lines containing that word. This functionality allows users to effectively sift through large amounts of data to find the information they need quickly and efficiently.

The other choices refer to unrelated tasks: executing commands in new terminal windows requires different utilities like 'xterm' or 'gnome-terminal'; managing user permissions is typically handled via commands such as 'chmod' or 'chown'; and displaying current disk usage is achieved through tools like 'df' or 'du'. Each of these tasks has its specific commands, illustrating the diverse functionality within the Linux environment.