Why do you need to traverse the entire hash? Just go directly to that key.

my %hash = (foo => 'bar', baz => 'biff');
my $scalar = $hash{foo};
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You should probably read perldoc perldata.

Traverse( \%yourhash, \$output, 'matchKey' );

sub Traverse{
    my $href = shift;
    my $oref = shift;
    my $match = shift;
    for my $key ( keys %$href ) {
        if ( ref( $href -> { $key }) eq 'HASH') {
            Traverse( $href -> { $key }, $oref );
        }
        else {
            ( $key eq $match ) and $$oref = $href -> { $key };
        }
    }
}
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What you have tried so far? You should go through perldata. Here is a small example.

%hash =("name" =>"john", "age"=>"25", "job"=>"programer", "location"=>
+"US");
while (($key, $val) = each %hash)
{
    if ($matchkey =~ /^$key$/)   #if matches the particular key
    {
    $var = $hash{$key};
     }
        
}
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or even simply,

$matchkey eq $_ ? $var = $hash{$_} : $var='' for keys %hash;
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still simply as davorg suggested

updated

That seems rather a long way to go about it. What does your method give you that simply using $var = $hash{$matchkey} doesn't?

Also why use $matchkey =~ /^$key$/ when $matchkey eq $key achieves the same thing without the overhead of invoking the regex engine? Regular expressions are a powerful tool, but they are often unnecessarily complex for the task in hand.

--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg