From: Dossy <dossy@...>
Date: 2002-05-20T08:53:21+09:00
Subject: Re: Need Multiline Regexp Help

On 2002.05.20, Jim Freeze <jim@freeze.org> wrote:
> Hi:
> 
> I am trying to collect a set of lines in a string.
> The line repeat a pattern, so I figured I could
> do a scan with a multi-line regexp to get what
> I wanted. But I am having trouble understanding
> what is happening. Can someone help?
> 
> irb(main):003:0> s="fred\nhello"
> "fred\nhello"
> irb(main):005:0> s.scan(/f.*[^l]/m) 
> ["fred\nhello"]   ## I thought [^l] would not match 'l'

f.* is matching "fred\nhell" -- "o" satisfies [^l].

> irb(main):006:0> s.scan(/(f.*)[^l]/m)
> [["fred\nhell"]]  ## Again, why the match of 'll'

(f.*) matches "fred\nhell" and "o" again satisfies [^l].

> irb(main):009:0> s.scan(/(f.*)[^lo]/m)
> [["fred\nh"]]     ## Why adding a second char changes the result?

Because now "o" doesn't satisfy [^lo] and neither does either
of the "ll".  Now, the "e" satisfies [^lo] so that (f.*) now
matches "fred\nh".

> irb(main):010:0> s.scan(/(f.*)[^ol]/m)
> [["fred\nh"]]

Changing the order doesn't matter.

-- Dossy

-- 
Dossy Shiobara                       mail: dossy@panoptic.com 
Panoptic Computer Network             web: http://www.panoptic.com/ 
  "He realized the fastest way to change is to laugh at your own
    folly -- then you can let go and quickly move on." (p. 70)