@my_filtered_keys = grep {exists $x{$_} && $x{$_} =~ /Yeah hoo!/} 1..10;

##</code><code>##

@my_filtered_vals = map {exists $x{$_} && $x{$_} =~ /Yeah hoo!/ ? $x{$_} : ()} 1..10;

##</code><code>##

#!/usr/bin/perl -wT
use strict;

my %x = ( 5 => 'a',
          6 => 'b',
          7 => 'Yeah hoo!',
          8 => 'd',
          9 => 'I said, Yeah hoo!',
         10 => 'f'
        );

print "K:$_\n" for grep {exists $x{$_} && $x{$_} =~ /Yeah hoo!/} 1..10;

print "V:$_\n" for map {exists $x{$_} && $x{$_} =~ /Yeah hoo!/ ? $x{$_} : ()}
                       1..10;

print "X:$_\n" for keys %x;

__END__

=head1 OUTPUT
K:7
K:9

V:Yeah hoo!
V:I said, Yeah hoo!

X:7
X:8
X:9
X:10
X:5
X:6