From: nobu.nokada@...
Date: 2002-08-10T22:23:29+09:00
Subject: Re: The problem with using $1 in regexps

Hi,

At Sat, 10 Aug 2002 10:07:07 +0900,
Philip Mak wrote:
> sub _num_quotes {
>     $_[0] =~ /^(>+)/;
>     return length($1);
> }

# If you were really made a subroutine, you must not meet the
# problem.

> See the problem in the above subroutine? (It's Perl, but the $1
> problem applies to Ruby too.) The subroutine is meant to return the
> number of '>' marks at the beginning of a line. However, I
> (mistakenly) wrote a regular expression that will fail to match if
> there are no '>' marks. If it fails to match, I end up returning the
> length of an uninitialized variable. This slipped past my unit tests
> since in the tests, $1 would always start out undefined. The simple
> bug of using /^(>+)/ instead of /^(>*)/ took me a while to track down.

Recent versions clear $1 and so on when match failed.

$ cat a.rb
NUM_QUOTES = /^(>+)/
NUM_QUOTES =~ ">>>a"
p $1
NUM_QUOTES =~ "a>>>"
p $1
$ ruby-1.6 -v a.rb
ruby 1.6.7 (2002-08-01) [i686-linux]
">>>"
nil

-- 
Nobu Nakada