John Bambenek - grep Pocket Reference

Copyright 2009 John Bambenek and Agnieszka Klus

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Chances are that if youve worked for any length of time on a Linux system, either as a system administrator or as a developer, youve used the grep command. The tool is installed by default on almost every installation of Linux, BSD, and Unix, regardless of distribution, and is even available for Windows (with wingrep or via Cygwin).

GNU and the Free Software Foundation distribute grep as part of their suite of open source tools. Other versions of grep are distributed for other operating systems, but this book focuses primarily on the GNU version, as it is the most prevalent at this point.

The grep command lets the user find text in a given file or output quickly and easily. By giving grep a string to search for, it will print out only lines that contain that string and can print the corresponding line numbers for that text. The simple use of the command is well-known, but there are a variety of more advanced uses that make grep a powerful search tool.

The purpose of this book is to pack all the information an administrator or developer could ever want into a small guide that can be carried around. Although the simple uses of grep do not require much education, the advanced applications and the use of regular expressions can become quite complicated. The name of the tool is actually an acronym for Global Regular-Expression Print, which gives an indication of its purpose.

GNU grep is actually a combination of four different tools, each with its unique style of finding text: basic regular expressions, extended regular expressions, fixed strings, and Perl-style regular expression. There are other implementations of grep -like programs such as agrep, zipgrep, and grep-like functions in .NET, PHP, and SQL. This guide will describe the particular options and strengths of each style.

The official website for grep is http://www.gnu.org/software/grep/. It contains information about the project and some brief documentation. The source code for grep is only 712 KB, and the current version at the time of this writing is 2.5.3. This pocket reference is current to that version, but the information will be generally valid for earlier and later versions.

As an important note, the current version of grep that ships with Mac OS X 10.5.5 is 2.5.1; however, most of the options in this book will still work for that version. There are other grep programs as well, in addition to the one from GNU, and these are typically the ones installed by default under HP-UX, AIX, and older versions of Solaris. For the most part, the regular expression syntax is very similar between these versions, but the options differ. This book deals exclusively with the GNU version because it is more robust and powerful than other versions.