Hi Guys,

I have a little test program here, which works fine, but I am not sure if there really is a predefined variable in perl called %_
I know there is a $_ and @_ but perldoc perlvar mentions nothing..

In the regex, I use the construct $_{$1}++ which is incrementing an element in a hash.
Which I was surprised worked. (even with strict!).
I wondered whether there was something more mysterious happening here.

Any ideas?

B

Code:

#!/software/perl/5.8.0/bin/perl use warnings; use strict; my $word='casablanca'; # Remove duplicate characters from $word # ie. casablanca = casbln $word=~s/(\w)/($_{$1}++)?'':$1/ge; print "word= ".$word."\n";

You code works just as well if you replace %_ with %", or with %demo (but in that latter case you must declare it through "my").

I don't think there's a special has %_ .... and there's certainly not a special %" - I think it's simply that strict allows the special variables en block, just like it allows $a and $b.  

Odd though, isn't it, that the docs don't seem to mention it.
@_ and $_ get a mention. Perhaps the criteria for 'un'strictness is <sigil>_

What I was doing was trying to avoid using a temporary hash to squeeze the operation into 1 line.
On second thoughts though, it's a poo idea as %_ needs to be cleared between subsequent uses, and a temp hash would be cleaner.

Code:

#!/usr/local/bin/perl use warnings; use strict; my $word='casablanca'; # Remove duplicate characters from $word # ie. casablanca = casbln sub cleanup {        my $word=shift;        local %_;        $word=~s/(\w)/($_{$1}++)?'':$1/ge;        return $word; } print cleanup( 'casablanca' )."\n"; print cleanup( 'greatescape' )."\n";

Produces...
casbln
greatscp

And without the local, produces...
casbln
gretp

Which I guess is what you'd expect from a 'global'.

In case you were wondering, it was part of a bit of code used to decrypt some of the gchq challenge (http://www.gchq.gov.uk/codebreaking/index.html)

B

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