in reply to Re: regex & variable substitution
in thread regex & variable substitution

Excellent - that's spot on! OK, so I now have a question: doesn't the plain 
$lookup{$1}

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create the key (and assign a value of null) if the key does not exist? Is it not better to do either "defined" or "exists" for the key? Anyway, my failing was the braces - getting that right made it work. many thanks...


-- Ian Stuart
A man depriving some poor village, somewhere, of a first-class idiot.

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Re^3: regex & variable substitution
by holli (Abbot) on Jul 11, 2005 at 09:49 UTC
    No, the key will only autivify when you assign a value to it.

    Prove: 
    #!/usr/bin/perl
use strict;
use warnings;

use Data::Dumper;

my %h;

print $h{key} ? $h{key} : "nokey";

print "\n", Dumper (\%h);

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    See? The hash stays emtpy.

    Update: exists, defined and the check for truth do different things. Consider: 
    #!/usr/bin/perl
use strict;
use warnings;

my %h = ( a => "", b => undef, c => "true");

for ( qw(a b c d) )
{
    print "key: $_ is " . ($h{$_}         ? "" : "not ") . "true\n";
    print "key: $_ is " . (defined $h{$_} ? "" : "not ") . "defined\n"
+;
    print "key: $_ is " . (exists  $h{$_} ? "" : "not ") . "existing\n
+";
}

#key: a is not true
#key: a is defined
#key: a is existing
#key: b is not true
#key: b is not defined
#key: b is existing
#key: c is true
#key: c is defined
#key: c is existing
#key: d is not true
#key: d is not defined
#key: d is not existing

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    holli, /regexed monk/
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      That update is really very interesting, and very helpful! Thanks for posting it...


      -- Ian Stuart
      A man depriving some poor village, somewhere, of a first-class idiot.
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