From: Daniel DeLorme <dan-ml@...42.com>
Date: 2008-09-29T13:49:23+09:00
Subject: Re: multiline regexp and newlines

Markus Schirp wrote:
> So my Regexp is like:
> 
> "Match any character from the begin to the end of a string witch is not
> newline, and ensure there is at least one character, and to this match
> over multiple lines (so if there are multiple lines reject it)"
> 
> Results in /^[^\n]+$/m
> 
> My ruby 1.8.6 does:
> 
> /^[^\n]+$/m =~ "a\n" -> 0
> 
> without multiline flag the same:
> 
> /^[^\n]+$/ =~ "a\n" -> 0

The multiline flag only changes the meaning of "." to include the \n 
character. It doesn't change the meaning of ^ and $ which mean 
respectively "beginning of line" and "end of line". True true "beginning 
of string" metacharacter is not ^ but \A, and for "end of string" it's 
not $ but \z (or \Z if you want to allow a trailing \n on your string)

 >> "a\nb\n"[ /^.*$/ ]
=> "a"
 >> "a\nb\n"[ /\A.*\z/ ]
=> nil
 >> "a\nb\n"[ /\A.*\z/m ]
=> "a\nb\n"

Yeah, it's tricky.

--
Daniel