if (not defined $time{$recordNumber}){
  ...
}

[download]

You can also check with exists in hashes, the semantic is a little bit different.

Update: A bit explanation: == compares numbers, so in the expression $foo == undef the undef is promoted to 0 and compared with $foo - not what you want.

In reply to Re: hash undef? by moritz
in thread hash undef? by Anonymous Monk

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