my %hash = ( qw/ foo 1 bar 2 baz 3 / );

$array[$user_section] =~ s{
    ^ username => (.*) $
}{
    Dance( \%hash, $1 );
}xemg;

sub Dance {
   my( $vars, $one ) = @_;
   my $name = $vars->{$one};
   return "username => $name" if defined $name;
   die "no name for $one ";
}