Regular-Expressions.info - Regex Tutorial, Examples and Reference

A regular expression (regex or regexp for short) is a special text string for describing a search pattern. You can think of regular expressions as wildcards on steroids. You are probably familiar with wildcard notations such as *.txt to find all text files in a file manager. The regex equivalent is .*\.txt$.

But you can do much more with regular expressions. In a text editor like EditPad Pro or a specialized text processing tool like PowerGREP, you could use the regular expression \b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b

to search for an email address. Any email address, to be exact. A very similar regular expression (replace the first \b with ^ and the last one with $) can be used by a programmer to check if the user entered a properly formatted email address. In just one line of code, whether that code is written in Perl, PHP, Java, a .NET language or a multitude of other languages.

Regular Expression Quick Start

If you just want to get your feet wet with regular expressions, take a look at the one-page regular expression quick start. While you can't learn to efficiently use regular expressions from this brief overview, it's enough to be able to throw together a bunch of simple regular expressions. Each section in the quick start links directly to detailed information in the tutorial.

Complete Regular Expression Tutorial

Do not worry if the above example or the quick start make little sense to you. Any non-trivial regex looks daunting to anybody not familiar with them. But with just a bit of experience, you will soon be able to craft your own regular expressions like you have never done anything else. The free Regular-Expressions.info Tutorial explains everything bit by bit.

This tutorial is quite unique because it not only explains the regex syntax, but also describes in detail how the regex engine actually goes about its work. You will learn quite a lot, even if you have already been using regular expressions for some time. This will help you to understand quickly why a particular regex does not do what you initially expected, saving you lots of guesswork and head scratching when writing more complex regexes.

Applications & Languages That Support Regexes

There are many software applications and programming languages that support regular expressions. If you are a programmer, you can save yourself lots of time and effort. You can often accomplish with a single regular expression in one or a few lines of code what would otherwise take dozens or hundreds.

Not Only for Programmers

If you are not a programmer, you use regular expressions in many situations just as well. They will make finding information a lot easier. You can use them in powerful search and replace operations to quickly make changes across large numbers of files. A simple example is gr[ae]y which will find both spellings of the word grey in one operation, instead of two. There are many text editors and search and replace tools with decent regex support.

Further Reading

If you're hungry for more information on regular expressions after reading this website, there are a variety of books on the subject.

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Welcome

New! PowerGREP 4

PowerGREP is probably the most powerful regex-based text processing tool available today. A knowledge worker's Swiss army knife for searching through, extracting information from, and updating piles of files.

Use regular expressions to search through large numbers of text and binary files. Quickly find the files you are looking for, or extract the information you need. Look through just a handful of files or folders, or scan entire drives and network shares.

Search and replace using text, binary data or one or more regular expressions to automate repetitive editing tasks. Preview replacements before modifying files, and stay safe with flexible backup and undo options.

Use regular expressions to rename files, copy files, or merge and split the contents of files. Work with plain text files, Unicode files, binary files, compressed files, and files in proprietary formats such as MS Office, OpenOffice, and PDF. Runs on Windows 2000, XP, Vista, and 7.

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