Question

Is there a list of Regex implementations on the web, showing their differences / similarities?

For exaple, Emacs elisp Regex is different to JavaScript or Perl regex, not to mention all the different implementations used by different editor software,

e.g. VS2010 uses {} instead of () to group expressions for back references.

Once upon a time I could rely on a Regex conversion list in O’Reilly’s Regex Pocket Quick Reference, but something online would be so much easier, and complete.

By the way, I am aware of (of course) http://www.regular-expressions.info/ which is good, but no where near complete.

I’ll compile a list from the answers posted here, and anything else I can find.

Variations

General Variations

The differences in implementations are usually the way special characters {}()[]^$ are handled (escaping rules etc.), and occasionally substituted; the handling/availability of POSIX character classes e.g. [:digit:], and the use of options, e.g. g i etc.

(a work in progress, if you know any caveats, differences for these implementations please add them as an answer)

• ActionScript – uses ECMA style
• Delphi (.Net) – Uses .Net style. Delphi Win32 has no native regex, but PCRE wrappers are available.
• Emacs/ELisp – has 2 different contexts, escaping uses \\ in elisp, and \ in regexp-replace. Special chars (){}[] are escaped when using them for regex features, much like sed.
• Eclipse – Search uses Java style regex.
• GNU (Linux) – POSIX BRE / ERE
• Grep – POSIX BRE / ERE
• Groovy – Uses Java style.
• IntelliJ
• Java – Java style.
• JavaScript – uses ECMA style.
• NetBeans
• .NET – Uses the classes in System.Text.RegularExpressions
• Notepad++ – PCRE
• PCRE (C/C++) – Open source library, used by many third party languages and apps. (e.g. PHP, TCL, R etc.)
• Perl – Perl style
• PHP – POSIX ERE, PCRE, (PHP5’s multibyte string module uses Oniguruma)
• POSIX – BRE (Basic Regex), ERE (Extended Regex)
• PowerShell – .Net style
• Python – Python style
• R – POSIX ERE/BRE, PCRE
• REALbasic – PCRE
• Ruby – Oniguruma
• Sed – special chars (){}[] are escaped when using them for regex features.
• Tcl – Three flavors, Tcl ARE (advanced regex), POSIX ERE, POSIX BRE.
• TextMate – Oniguruma
• Tera Term – Oniguruma
• VBScript – ECMA
• Visual Basic 6 – ECMA (when using Microsoft VBScript Regular Expressions 5.5 COM object)
• Visual Studio – Grouping braces are {} (more details to follow.)
• wxWidgets – Tcl ARE, POSIX BRE/ERE
• XML Schema – XML
• XQuery & XPath – Xpath

Additional references.

• Wikipedia’s List of regular expression software
• Regex info’s comparison of Regex flavors

Answer 1

Take a look at the Regular Expression Flavor Comparison on Regular-Expressions.info. It contains at least the nowadays most important regular expression implementations and their characteristics.