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- Regular expression tester with syntax highlighting, PHP / PCRE & JS Support, contextual help, cheat sheet, reference, and searchable community patterns. RegExr is an online tool to learn, build, & test Regular Expressions (RegEx / RegExp).
- In our Regular Expressions Cheat Sheet, we include essential Java classes and methods, RegEx syntax, character classes, boundary matchers, logical operations, quantifiers, groups, backreferences, and pattern flags. You can download the Java RegEx Cheat Sheet, below. Download the Cheat Sheet.
This page explains what makes this site special among all other regex sites, but first let's answer a burning question:
What is the meaning of life?
That's easy. As per the regex humor page, it's simply
Now for the other burning question…
What is a Regex?First, a regex is a text string. For instance, foo is a regex. So is [A-Z]+:d+.
Those text strings describe patterns to find text or positions within a body of text. For instance, the regex foo matches the string foo, the regex [A-Z]+:d+ matches string fragments like F:1 and GO:30, and the regex (?<=[a-z])(?=[A-Z]) matches the position in the string CamelCase where we shift from a lower-case letter to an upper-case letter.
Typically, these patterns (which can be beautifully intricate and precise) are used for four main tasks: to find text within a larger body of text; to validate that a string conforms to a desired format; to replace text (or insert text at matched positions, which is the same process); and to split strings.
For instance, the CamelCase pattern from the last paragraph can be used to split MyLovelyValentine into its three component words. And you could use the regex _d+_ to find digits within underscores (as in _12_) and to replace the underscores with double dashes, yielding --12--, something you could not do with a conventional search-and-replace (details for that technique are in the recipe about replacing one delimiter with another).
Let's compress the definition from the earlier paragraphs:
Is a Regex the same as a Regular Expression?
R Regular Expression PdfMostly yes, with a little bit of no. At this stage, this is a semantic question—it depends on what one means by regular expression. That topic and other juicy details are discussed on the page about Regex vs. Regular Expressions.
About this SiteBefore we dive in—and only if you have time—I'd like to introduce this site and what makes it special.
I love regular expressions. They are a small computer language of their own.
When I was a young dinosaur, I didn't take the time to properly learn the syntax, largely because I really didn't feel like learning another language. Who needs regex, I thought, when your programming language has functions that let you dig into strings from the left, the middle and the right?
What's more, the raw syntax you usually see in code that contains regexes used to intimidate me. Who wants to deal with a language that looks like this?
(?s)/*(?:(?!*/)[*$ _/+-])*(.*?)[*$ _/+-]*?*/
No doubt about it, even with comments and breathing room, there is something raw and experimental about writing a regex pattern.
Besides, how well your pattern performs doesn't only depend on applying correct syntax. There are several ways of doing things, and various regex engines may optimize some of these ways behind your back.
With regex, you are stepping down to a fairly low level, within earshot of the machine room. I like that. And I've been liking it all the more since learning about tools and safeguards to keep me from falling into the boiler.
A (hopefully) Different Presentation of Regex
RexEgg tries to present regular expressions a bit differently, in the hope that these different angles help many people become more grounded in their knowledge of regex. If you are looking for a drawn-out primer, this is not the place, as I don't see the need to pollute our beautiful world wide web with another explanation of how to match 'foo' in 'foo bar'. But if you take your time to read the carefully-built tables on the quick-launch page then perhaps the page about (? … ) syntax, you will experience what may be the most accelerated regex introduction around.
What Will you Find on this Site
✽ A step-by-step explanation of simple and advanced regular expressions crafted for various contexts (such as text matching, file renaming, search-and-replace).
✽ A presentation of the many contexts where you may run into regular expressions (from Apache to your html editor and file manager), complete with examples.
✽ A reference about (? … )—to reduce confusion by bringing all the pieces of syntax that start with an opening parenthesis and a question mark into a single place.
✽ A discussion of Conditional Regexes, a topic about which there is little information.
✽ A discussion of Recursive Regexes, a topic about which there is very little information.
Regex R Cheat Sheet Free
✽ Pages dedicated to regex in C#, Python, PHP and other languages.
✽ Plenty of tips & tricks.
✽ Sections about regex tools and regex books.
✽ And much more!
I wish you lots of fun on your journey with regular expressions.
and The Best Regex Trick Ever!!!
Quick-Start: Regex reference table
When learning regexes, or when you need to use a feature you have not used yet or don't use often, itcan be quite useful to have a place for quick look-up. I hope this Regex Cheat-sheet will provide such aid for you.
Regex Character Classes and Special Character classes.
TODO: add examples w and d matching unicode letters and numebers.
'Quantifier-modifier' aka. Minimal Matching
Grouping and capturing
Other Regex related articles
Published on 2015-08-19