You need to escape '.' in the regular expression like this:

  split /\./

'.' in a regular expression matches any single character, rather than the period character.

Please have a look through perlre.

Personally, I like to do:

  
  my ($whole,$fract) = ($hjd =~ /(\d+)(\.\d+)?/);
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If $fract isn't defined, it'll be evaluated as zero when used numerically.

-David