That's interesting - I wondered if that could be used to modify the hash key without creating a copy of the whole hash so tried: 
use Data::Dump qw(dump); 

my %hash = (
  key1 => 'Value1',
  key2 => 'Value2',
  key3 => 'Value3',  );

print "old hash is " . dump(\%hash) ."\n";
map { s/2/_two/; } %hash;
print "new hash is " . dump(\%hash) ."\n";

# output is:
# old hash is { key1 => "Value1", key2 => "Value2", key3 => "Value3" }
# new hash is { key1 => "Value1", key2 => "Value_two", key3 => "Value3
+" }

[download]
How come 'Value2' is changed to 'Value_two', but 'key2' is unchanged?

(Note: I wasn't suggesting that this method should be used for modifying a hash key, but was trying to rise to the challenge of suggesting another method other than copy and delete!)

In reply to Re^3: Modifying the keys in a hash by sluap
in thread Modifying the keys in a hash by Mandrake

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.