From: Brian Candler <B.Candler@...>
Date: 2003-05-13T16:10:36+09:00
Subject: Re: Regexp: why does (re)* return only last repetition?

On Tue, May 13, 2003 at 12:02:06PM +0900, Austin Ziegler wrote:
> 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\\]"

Now try:
          a = "[a-z\\]"
          p a.length                         # => 6
          a.each_byte { |c| puts "%c" % c }  # => [ a - z \ ]

irb is deceiving you, because 'inspect' outputs strings in a way which can
be re-input as strings into Ruby. A single backslash is printed as two
backslashes.

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

And single-quoted strings have the same issue it turns out:

          a = '\\'
          p a.length   # => 1

I am not sure why that should be, since '\n'.length is 2. I think you may
have uncovered a bug here.

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

"\a" in a double-quoted string is a 'BEL' (a for Audible), ASCII code 7

irb(main):001:0> "\a"[0]
=> 7

Brian.