From: Mike Stok <mike@...>
Date: 2010-09-27T11:03:25+09:00
Subject: Re: bug in gsub(?)


On Sep 26, 2010, at 9:40 PM, Chad Perrin wrote:

> On Sun, Sep 26, 2010 at 03:54:35PM +0900, Brian Candler wrote:
>> Chad Perrin wrote:
>>> I've wondered for quite a while what was the rationale for having \1 in
>>> the first place.
>> 
>> Ruby inherits a lot from Perl, and Perl from sed.
> 
> Okay . . . I guess that sorta makes sense.  Of course, I've never used \1
> in Perl, nor seen anyone else do so either, so until you mentioned it I
> had entirely forgotten that was an option there either.
> 
> Both languages would be better off without that syntax, and just stick
> with $1 instead, I think.
> 
> 
>> 
>> Some of the Perlisms are IMO superfluous - in particular the Kernel 
>> methods which operate on $_, and the flip-flop conditional operators.
> 
> I wouldn't really call \1 a "Perlism", given that the way I've always
> seen it done is with $1 instead.  If it's a Perlism despite its lack of
> general usage, I'd say it's every bit as much a Rubyism.

There are times in Perl when you need to use \1 in the matching part of a regular expression because you don't want $1 to interpolate into the match.

Consider trying to match a simple quoted string (i.e. no \ escaping):

my $s1 = "Hello there";
my $s2 = q{The cat said "Hello there, how's it going?"};

if ($s1 =~ m/(ell)/) {
    print "print s1 matched - \$1 is '$1'\n";
}

if ($s2 =~ m/(["'])(.*?)\1/) {
    print "print s2 matched - \$2 is '$2'\n";
}

This outputs:

print s1 matched - $1 is 'ell'
print s2 matched - $2 is 'Hello there, how's it going?'


If you try using $1 in place of \1 in the second regex then it will output

print s1 matched - $1 is 'ell'
print s2 matched - $2 is 'H'


Mike

-- 

Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.