Given that delete can delete a slice, this can be simplified:

my %map = (...);
@$h{values %map} = delete @$h{keys %map};
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Update: note that this doesn't break on %map = (foo => 'bar', bar => 'foo') that the solutions above may do.

lodin

Given that initializing the hash just requires you list a bunch of keys and values, this can be simplified:

@{$h}{qw/ month year day first_name /}= delete  # New keys
@{$h}{qw/ mm    yyyy dd  name /};               # Old keys
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Yeah, I added some extra braces.

- tye        

@{$h}{qw{month year day first_name}} = delete @{$h}{qw{mm yyyy dd name
+}};

C:\@Work\Perl>perl -wMstrict -e
"my $h = { mm => 'July', yyyy => '1975', dd => '31', name => 'Milo', l
+ast_name => 'Manara',};
print qq(o/p: \n);  print qq($_ => $h->{$_} \n) for keys %$h;
@{$h}{qw{month year day first_name}} = delete @{$h}{qw{mm yyyy dd name
+}};
print qq(-----\n);  print qq($_ => $h->{$_} \n) for keys %$h"
o/p:
mm => July
name => Milo
dd => 31
last_name => Manara
yyyy => 1975
-----
month => July
day => 31
first_name => Milo
year => 1975
last_name => Manara
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