From: Austin Ziegler <austin@...>
Date: 2003-05-13T12:02:06+09:00
Subject: Re: Regexp: why does (re)* return only last repetition?

On Tue, 13 May 2003 07:54:02 +0900, Brian Candler wrote:
> On Tue, May 13, 2003 at 07:29:24AM +0900, Austin Ziegler wrote:
>> You changed the pattern.
>> 
>> 1 | pat = "[a-z\\]"
>> 2 | str = "abcd\\efgh"
>> 3 | index = /#{pat}/ =~ str
>> 4 | p index
>> 
>> line 3 results in:
>> RegexpError: premature end of regular expression: /[a-z\]/
> Double-quoted strings interpolate backslashes: so in your example
> pat contains:
> [a-z\]

No:
  irb(main):001:0> "[a-z\\]"
  => "[a-z\\]"

It's rather irrelevant anyway, as the *exact same behaviour* happens
with single-quoted strings (change line 1 to '' instead of "").

>> Change the pattern to "[\\a-z]" and the error goes away.
> Yes, that's
> [ \ a - z ]

No:
  irb(main):008:0> "[\\a-z]"
  => "[\\a-z]"

> I guess '\a' is treated as just 'a' in a character class.

No:
  irb(main):009:0> /[\a]/ =~ "abc\a"
  => 3

This behaviour is in both 1.6.8 and 1.8.0 (2003-05-09). I really
think that it's a bug because [\\a-z] and [a-z\\] should be
semantically equivalent. It works when done as a literal; it doesn't
work when substitution is done.

-austin
-- Austin Ziegler, austin@halostatue.ca on 2003.05.12 at 22:54:26