RegEx standards across languages

regex

I am asking this question because I notice there are some slight differences in the syntax of RegEx between different languages.

I am wondering if there is a RegEx standard that is maintained somewhere? And if so, where can I find this document? Also, if I create a RegEx expression in .NET, is the same expression guaranteed to be 100% compatible and work with other languages, such as Perl or Javascript or Java?

Finally, are there any "best practices" when it comes to using RegEx that can help to make it more maintainable across other platform languages?

Best Answer

One of the oldest sets of standardized regular expressions are the POSIX BRE (basic regular expressions) and ERE (extended regular expressions), documented under Regular Expressions.

Other languages may define their own standards. For example, C++ 2011 has a regular expression library defined in clause 28 (about 46 pages of standard). Perl defines its regular expressions. Other languages borrow from these sources and others. Lex and Flex use their own set of regular expressions. Sed uses its own variant on regular expressions. And Java, JavaScript, and ... define their own versions, sometimes using PCRE (Perl-Compatible Regular Expressions) as the basis for their design. Some of the details are affected by the facilities provided by the language in which the regular expressions are being used.

Jeff Friedl's book Mastering Regular Expressions covers a lot of different sets of regular expressions, identifying what's common and what's different.

Related Solutions

Regex – Can you make just part of a regex case-insensitive

Perl lets you make part of your regular expression case-insensitive by using the (?i:) pattern modifier.

Modern regex flavors allow you to apply modifiers to only part of the regular expression. If you insert the modifier (?ism) in the middle of the regex, the modifier only applies to the part of the regex to the right of the modifier. You can turn off modes by preceding them with a minus sign. All modes after the minus sign will be turned off. E.g. (?i-sm) turns on case insensitivity, and turns off both single-line mode and multi-line mode.

Not all regex flavors support this. JavaScript and Python apply all mode modifiers to the entire regular expression. They don't support the (?-ismx) syntax, since turning off an option is pointless when mode modifiers apply to the whole regular expressions. All options are off by default.

You can quickly test how the regex flavor you're using handles mode modifiers. The regex (?i)te(?-i)st should match test and TEst, but not teST or TEST.

Source

Regex – How to match all occurrences of a regex

Using scan should do the trick:

string.scan(/regex/)

Best Answer

Related Solutions

Regex – Can you make just part of a regex case-insensitive

Regex – How to match all occurrences of a regex

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