length returns the length in characters of given argument

keys in scalar context (your case) returns numner of keys ina hash

So if your hash has 153 keys than length '153' returns 3 i.e. three characters

change you code as: 

print "there are @{[scalar keys %common]}:\n";

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In reply to Re: what's wrong with this? by ccn
in thread what's wrong with this? by Alien

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