$size = keys %somehash;
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Will work just fine.

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

"size of a hash" isn't really well defined. You can get the number of keys, or the number of values pretty easily. (does a key w/o a defined value count? It might not for some purposes). You can cut down the keystrokes on your method with something like the following:

print "This hash holds ". scalar keys %somehash . " keys\n";
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HTH

perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n";*other_name = *rose;print "$other
+_name\n"'
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%somehash = ( key1 => "value1",
              key2 => "value2",
              key3 => "value3,
              key4 => "value4",
             );
$size = keys %somehash;
print "This hash holds $size key-value pairs\n";
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If you evaluate a hash in a scalar context, it returns a value which is true if and only if the hash contains any key/value pairs. (If there are any key/value pairs, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash. This is pretty much useful only to find out whether Perl's (compiled in) hashing algorithm is performing poorly on your data set. For example, you stick 10,000 things in a hash, but evaluating %HASH in scalar context reveals "1/16", which means only one out of sixteen buckets has been touched, and presumably contains all 10,000 of your items. This isn't supposed to happen.)