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It's all fun and games until you find out that the meaning of a regex is implementation specific. I've found that a Python regex will accept an unspecified newl

It's all fun and games until you find out that the meaning of a regex is implementation specific. I've found that a Python regex will accept an unspecified newline byte/character before the $, while std::regex in GNU C++11 will not.

robert_tweed 10y ago
This is very true and it always bugs me when some application or API supports regex, but the documentation doesn't specify the grammar, usually saying it's "standard regular expressions" - which standard? Posix? PCRE? Something else? Almost every flavour has some subtle differences and it's really, really important to know what you are dealing with. I do feel like these subtle differences are the main cause of bugs in programs containing regexes; compounded by the fact they aren't super-readable, especially for people who don't use them frequently. Tools like this are IMO really valuable for code reviews and it's nice to see that this one does have a flavour switch on the LHS with some of the main implementations.
- OskarS 10y ago
  I also can never remember which characters are magic and which are literal in different implementations. This is mostly Vim's fault, where the rules are impossible to remember and often conflict with other implementations. Given that it's the most common regex thing I use day-to-day, it's very annoying.
  - EvilTerran 10y ago
    Yeah, I agree, vim's default regex syntax is infuriatingly inconsistent. I pretty much always start my REs with "/\v"[0], to the point it's in my muscle memory: I'll find myself looking at that in the cmdline before I've even drafted the pattern in my head. (Then sometimes I'll realise I just want to find an exact string full of symbols, and have to back up and capitalize the "v".) ... I should probably come up with some mappings so the \v is inserted automatically. [0] http://vimdoc.sourceforge.net/htmldoc/pattern.html#/\v http://vimdoc.sourceforge.net/htmldoc/pattern.html#/\v

robert_tweed 10y ago

This is very true and it always bugs me when some application or API supports regex, but the documentation doesn't specify the grammar, usually saying it's "standard regular expressions" - which standard? Posix? PCRE? Something else? Almost every flavour has some subtle differences and it's really, really important to know what you are dealing with. I do feel like these subtle differences are the main cause of bugs in programs containing regexes; compounded by the fact they aren't super-readable, especially for people who don't use them frequently. Tools like this are IMO really valuable for code reviews and it's nice to see that this one does have a flavour switch on the LHS with some of the main implementations.

OskarS 10y ago
I also can never remember which characters are magic and which are literal in different implementations. This is mostly Vim's fault, where the rules are impossible to remember and often conflict with other implementations. Given that it's the most common regex thing I use day-to-day, it's very annoying.
- EvilTerran 10y ago
  Yeah, I agree, vim's default regex syntax is infuriatingly inconsistent. I pretty much always start my REs with "/\v"[0], to the point it's in my muscle memory: I'll find myself looking at that in the cmdline before I've even drafted the pattern in my head. (Then sometimes I'll realise I just want to find an exact string full of symbols, and have to back up and capitalize the "v".) ... I should probably come up with some mappings so the \v is inserted automatically. [0] http://vimdoc.sourceforge.net/htmldoc/pattern.html#/\v http://vimdoc.sourceforge.net/htmldoc/pattern.html#/\v