From: Brian Candler <B.Candler@...>
Date: 2003-05-13T07:54:02+09:00
Subject: Re: Regexp: why does (re)* return only last repetition?

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 \ ]

which is not a valid RE, because it has no terminating close-bracket.
\] means "match a literal ]", so you have

      [        start of character class
      a        first character in range
      -        range separator
      \]       last character in range

but no 'end of character class'

It's the same with /.../ delimiters:

irb(main):001:0> /[a-z\]/
SyntaxError: compile error
(irb):1: premature end of regular expression: /[a-z\]/
        from (irb):1

> Change the pattern to "[\\a-z]" and the error goes away.

Yes, that's

      [ \ a - z ]

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

It's not 'match start of string' anyway, as that doesn't make sense in a
character class...

Regards,

Brian.