From: Brian Candler <B.Candler@...>
Date: 2003-04-27T21:04:33+09:00
Subject: Re: Regexp and $

On Sun, Apr 27, 2003 at 08:41:04PM +0900, I wrote:
> This means the description "$ matches end of string or before \n" is wrong
> for Ruby. In fact, I'm not sure *what* exactly $ matches. Can anybody give
> me a description of what $ matches in Ruby?

The closest description I can come up with is:

  In Ruby, '$' matches:
  - before a newline
  - at the end of the string, UNLESS the last character of the string is a
    newline, in which case it doesn't match there.

irb(main):001:0> a = "abc\n\n"
=> "abc\n\n"
irb(main):002:0> a.gsub(/$/,'z')
=> "abcz\nz\n"
irb(main):003:0> a = "abc"
=> "abc"
irb(main):004:0> a.gsub(/$/,'z')
=> "abcz"

I wonder why this was chosen rather that just "'$' matches before a newline
*and* at the end of the string"?

I guess if you do gsub(/$/,'foo') to add text to the end of a \n-terminated
line then it kind of makes sense. But it does stop you matching /\n$/ if you
want to explicitly eat up newlines - and breaks compatibility with other
languages.

'^' doesn't have this issue:

irb(main):005:0> b = "\nabc"
=> "\nabc"
irb(main):006:0> b.gsub(/^/,'z')
=> "z\nzabc"

So '^' always matches at the start of the string *and* after a newline.

Regards,

Brian.