$ perl -e'
   use v5.14;
   use experimental qw( for_list );

   my %h = ( a => 4, b => 6 );
   my $i = 0;
   for my ( $k, $v ) ( %h ) {
      if ( !$i++ ) { ++$h{a}; ++$h{b}; }
      say "$k:$v";
   }
'
a:5
b:7