How similar are the Regular expressions engines for PHP, MySQL, JavaScript, Perl, etc?

Are regular expressions the same for PHP, MySQL, JavaScript, Perl, and so on? If so, is there a ch开发者_运维技巧art or tutorial that explains regular expressions?

No, there often are subtle differences in supported features (mostly of the pretty advanced kind¹). For example, JavaScript regular expressions don't have lookbehind. PHP uses either POSIX extended regular expressions or PCRE (Perl-compatible regex), which are close to Perl's feature-set. In fact, Perl is probably the ancestor of many advanced features in today's regular expression engines.

As for tutorials and comparisons the site http://regular-expressions.info is a very good resource.

Once you got used to writing and applying them it often is helpful to just quickly try out things. I have found a REPL to be quite handy; I usually use Windows PowerShell but Ruby or Python are also pretty popular.

¹ Thanks, Dancrumb.

In theory regular expression is a language for pattern matching.But there are little differences from language to language . My advice is use a tool like Regex Coach to building/learning regular expressions.

There is an excellent write-up of Perl regular expressions compared to "classic", POSIX and GNU grep in Chapter 3 of the book "Minimal Perl" by Tim Maher. And I think it's a good read for any of them, not just Perl.

And what do you know, "Sample Chapter 3" is available as a download from this page: Minimal Perl book!