How Linux Works

Intermediate Commands

The following sections describe the most essential intermediate Unix commands beyond the basics that you saw earlier in this chapter. There are many more commands where these come from; check out Appendix A for a large list of commands on your system.

grep

grep prints the lines from a file or input stream that match an expression. For example, if you want to print the lines in the /etc/passwd file that contain the text root, use this command:

grep root /etc/passwd

The grep command is extraordinarily handy when operating on multiple files at once, because it prints the filename in addition to the matching line when in this multiple-file mode. For example, if you want to check on every file in /etc that contains root, you could ...