my %hash = (tom => 23, larry=> 't0', tina=> 23);

my @filteredhash = grep{/^t/} keys %hash;
my %newhash = map{$_, $hash{$_}} @filteredhash;

##</code><code>##

my %newhash = map{$_, $hash{$_}} grep{/^t/} keys %hash;