FAQ: Where to find REGular EXpressions (RegEx) documentation ?

guy038

Hello and welcome to the FAQ Desk. You have likely been directed here because you asked about N++ regex flavor, [ N++ ] regex documentation or N++ regex enhancements.

Preliminary Note : As recalled recently by @peterjones, our forum is not a professional regex-writing forum. We are users of Notepad++, who want to help others learn more about NPP (and learn more ourselves, in the process). Since Notepad++ makes use of regular expressions, we will often provide help with regex questions

Our present regex engine is implemented since Ascii and Unicode version 6.0 of Notepad++ and improved till the v6.4.2 version, by, both, Dave BrotherStone and François-R Boyer. Previously, It used the Regex library, of the Boost C++ libraries v1.55.0, similar to the PERL Regular Common Expressions v5.8

Starting with Notepad++ v7.7, it currently used the Boost C++ regex library v1.70.0. Since this release, the Backtracking Control Verbs are supported. Refer to the link, below, for information on this new feature :

https://community.notepad-plus-plus.org/post/55464

Since Notepad++ v8.2, the current Boost C++ regex library is the release v1.78.0

Notepad++ v8.4.7 switched to Boost C++ regex library v1.80.0

For noob people, about regular expressions concept and syntax, begin with that article, elaborated by Peter Jones and part of the Notepad++ Documentation :

https://npp-user-manual.org/docs/searching/#regular-expressions

Note that the old link of the outdated Notepad++ Wiki ( http://docs.notepad-plus-plus.org/index.php/Regular_Expressions ) as well as the temporary link, on GitHub ( http://notepad-plus-plus.github.io/npp-usermanual/content/searching/ ) are, from now on, obsolete

In addition, whatever its level, anyone will find good documentation, about the regex library; of the Boost C++ libraries v1.80.0, from the two addresses below :

http://www.boost.org/doc/libs/1_80_0/libs/regex/doc/html/boost_regex/syntax/perl_syntax.html

http://www.boost.org/doc/libs/1_80_0/libs/regex/doc/html/boost_regex/format/boost_format_syntax.html

The FIRST link explains the syntax, of regular expressions, in the SEARCH part.
The SECOND link explains the syntax, of regular expressions, in the REPLACEMENT part.

And, possibly, take a glance at the Standards Conformance :

https://www.boost.org/doc/libs/1_80_0/libs/regex/doc/html/boost_regex/background/standards.html

You may, also, look for valuable information, on this non-exhaustive list of sites, below :

General Information :

https://en.wikipedia.org/wiki/Regular_expression

Summary of Regex Syntax ( Cheat Sheet and Basic Features ) :

https://www.regular-expressions.info/quickstart.html

http://www.rexegg.com/regex-quickstart.html

https://regex101.com/ — Quick Reference panel ( Thanks to Jim Dailey )

https://medium.com/factory-mind/regex-tutorial-a-simple-cheatsheet-by-examples-649dc1c3f285

https://ryanstutorials.net/regular-expressions-tutorial/ — Excellent introduction

https://www.geeksforgeeks.org/write-regular-expressions/

https://docs.python.org/2/howto/regex.html

https://docs.microsoft.com/en-us/dotnet/standard/base-types/regular-expression-language-quick-reference

https://www.debuggex.com/cheatsheet/regex/pcre

http://regexstorm.net/reference

Full Documentation and Advanced Information :

http://www.regular-expressions.info ( the REFERENCE ! )

http://www.rexegg.com

https://gammon.com.au/pcre/pcrepattern.html

http://www.pcre.org/pcre.txt

http://perldoc.perl.org/perlre.html

https://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean

Regex Testers :

https://www.regexbuddy.com — All flavors ( the REFERENCE ! )

https://regex101.com/ — PCRE , Python, JavaScript and Golang flavors

https://regexone.com/ — PCRE flavor

https://www.debuggex.com/ — JavaScript, Python and PCRE flavors ( Visual regex representation )

https://www.regextester.com/ — JavaScript and PCRE flavors

https://www.regexpal.com/ — JavaScript and PCRE flavors

https://www.freeformatter.com/regex-tester.html — JavaScript flavor

https://regexr.com/ — .NET flavor

Be aware that, as any documentation, it may contain some errors ! Anyway, if you’ve detected one, that’s good news : you’re improving ;-))

I highly recommend reading the contents of the third edition of the book Mastering Regular Expressions ( Understand your Data and Be More Productive ) by Jeffrey E. F. Friedl ( August 2006 ). If you find it of interest, just download this PDF file, of 534 pages.

Refer for an English version ( ISBN 0-596-52812-4 ) from the link, below :

https://doc.lagout.org/programmation/Regular Expressions/Mastering Regular Expressions_ Understand Your Data and Be More Productive (3rd ed.) [Friedl 2006-08-18].pdf

Quotations :

Some people, when confronted with a problem, think “I know, I’ll use regular expressions.” Now, they have two problems! — Jamie Zawinski

And, of course, one claimed precedence. One said: “I needed love, I got married. Then, I had two problems”! — Anonymous

REMARK :

After good practice, you will probably find out some unexpected results with our present N++ regex engine. In that case, you may try an old unofficial version, of the N++ regex engine, which corrects some bugs and adds some regex improvements :

Search and replacement are performed in true 32 bits code-points ( instead of UTF-16 )
So, it can handle ALL the Universal Character Names ( UCN) of the UCS Transformation Format , from \x{0} to \x{7FFFFFFF}, particularly, all those of code-points over \x{FFFF}, which are outside the BMP ( Basic Multilingual Plane )
Both, search and replace strings can contain embedded NUL characters and/or Escape sequences for NUL characters ( \x{0000} )
Backward assertions, as \A, are correctly supported ( OK with N++ since v7.9.1 )
Backward regex search does not stop, anymore, when matching a character with Unicode code-point over \x{00FF}
Look-behinds are correctly handled, when searching or replacing, even those overlapping with the end of the previous match ( OK with N++ since v7.9.1 )
A new [[:inval:]] character class, which allows you to find invalid UTF-8 sequences, which can be kept in replacement

IMPORTANT : Unfortunately, this beta version, created in May 2013, by François-R Boyer can not be run with N++ versions higher than v6.9.0. So, if you need that improved regex engine, for specific cases, use the following method, which can be processed, independently of the present N++ version(s), in your configuration :

Download an archive of Notepad++ v6.9.0, 32 Bits , from one of the links, below :

http://download.notepad-plus-plus.org/repository/6.x/6.9/npp.6.9.bin.7z

http://download.notepad-plus-plus.org/repository/6.x/6.9/npp.6.9.bin.zip

Extract all the contents of this archive, in a new directory
Rename the present SciLexer.dll file, as, for instance, SciLexer.OK
Download the François-R Boyer version of that dll, from :

https://sourceforge.net/projects/npppythonplugsq/files/Beta N%2B%2B regex code/SciLexer.dll/download

Place this new SciLexer.dll file, in this new N++ directory
Start Notepad++ v6.9.0
And…, enjoy any complicated regex search/replacement !

NOTE : You may, also, have a look to his readme.txt file from :

http://sourceforge.net/projects/npppythonplugsq/files/Beta N%2B%2B regex code/

MAPJe71

Additional Regex Tester tool (offline): RegEx Tester