Regex

Why PHP’s RegEx Is Slow, And What You Can Do About It (if you happen to be a committer on the PHP project)

Regular Expression Matching Can Be Simple And Fast, by Russ Cox:

Perl [and PHP and others] could not now remove backreference support, of course, but they could employ much faster algorithms when presented with regular expressions that don’t have backreferences.

How much faster? About a million times (no, I do not exaggerate).

I use a lot of regular expressions, and relatively few of them use backreferences. It’d be worth optimizing.

Matching Multi-line Regex in BBEdit

I love BBEdit on my Mac, but I was left scratching my head again today when I was trying to remember how to make its regex engine match a pattern across multiple lines. My hope was to extract a list of initial articles from a page that had HTML like this:

```  
amScottish Gaelic
anEnglish,Irish,Scots,Scottish Gaelic,Yiddish
an t-Irish,Scottish Gaelic
```

Indeed, it has well over 100 tables like that, and I was looking for the contents of the first TD in each. The following regex does it:

``` (?s)[^<]*<table>[^<]*<tr>[^<]*<td[^>]*>([^<]*)</td>.*?</table> ```

The most significant part of this is the (?s) at the beginning that tells BBEdit to match the pattern across line breaks. A more ninja-like regex assassin would probably be able to do it better, but this worked.