Explain this UTF-8 detection regex
php, regex
Solution
It's just an empty regular expression. `!` is the delimiter and `u` is the modfier.
As for why it works, from PHP Manual's description of the `u` modifier (emphasis mine):
This modifier turns on additional functionality of PCRE that is incompatible with Perl. Pattern strings are treated as UTF-8. This modifier is available from PHP 4.1.0 or greater on Unix and from PHP 4.2.3 on win32. UTF-8 validity of the pattern is checked since PHP 4.3.5.
Problem
This question asked how to detect UTF-8 strings - How to detect if have to apply utf8 decode or encode on a string? The solution was this: ``` if (preg_match('!!u', $string)) { // this is utf-8 } else { // definitely not utf-8 } ``` I haven't been able to figure out how to breakdown the "!!u" expression. I clicked through all of PHP's PCRE stuff and might have missed the description for "!" marks and "u"-somethings. I tried running it through perl's YAPE::Regex::Explain (as seen in Please explain this Perl regular expression) and couldn't get something that made sense [I'm no perl expert - don't know if I fed it the right expression/string]. So... how exactly does `preg_match('!!u', $string)` work?