$matching_key=grep { $_ =~ /$regex/  } keys %tax2loc;

##</code><code>##

@all_matching_keys = grep { $_ =~ /$regex/  } keys %tax2loc;
$matching_key = $all_matching_keys[0];

##</code><code>##

($matching_key) = grep { $_ =~ /$regex/  } keys %tax2loc;

##</code><code>##

$matching_key = first { $_ =~ /$regex/  } keys %tax2loc;

##</code><code>##

$matching_key = first { /$regex/ } keys %tax2loc;