Returns the length in characters of the value of EXPR.  If EXPR is
omitted, returns the length of $_
.  If EXPR is undefined, returns
undef.
This function cannot be used on an entire array or hash to find out how
many elements these have.  For that, use scalar @array
 and scalar keys
%hash
, respectively.
Like all Perl character operations, length() normally deals in logical
characters, not physical bytes.  For how many bytes a string encoded as
UTF-8 would take up, use length(Encode::encode_utf8(EXPR)) (you'll have
to use Encode
 first).  See Encode and perlunicode.