How to Use the Grep Command

Updated Friday, June 1, 2018 by Phil Zona Written by Phil Zona

In this guide, you’ll learn how to use the grep command. When performing administrative tasks on your Linode, many commands will give you more information than you need. Using grep allows you to filter that output in order to find only the data that’s relevant.

1. To search a file for a particular string, provide the string and filename as arguments:

   grep 'some text' /etc/ssh/sshd_config
   

2. You may also redirect output from a command to grep using a pipe:

   tail -f /var/log/apache/error.log | grep 'some text'
   

   This will monitor your Apache error logs, and display only the lines of output that contain the given string.

3. Regex patterns are also supported by the -E option if you want to search for a set of strings rather than one literal:

   grep -E "[[:alpha:]]{16,20}" /etc/ssh/sshd_config
   

   This example will search the /etc/ssh/sshd_config file for strings of alphabetic characters that are 16-20 characters long, but you can use any regex pattern you like.

These are simply a few basic ways to use grep. Many other options exist, and in combination with other tools, it serves as an invaluable utility for performing administrative tasks on your Linode. For more information on some of grep’s advanced features, check out our guide on how to search and filter text with grep.

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This guide is published under a CC BY-ND 4.0 license.