I am building a hash of arrays with information from 2 files. I would like to do something like 
 if ($hash{^$file}) { do something }

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First file gives me keys and the first 3 values of the list: 
  $hash{$thing} = (1,2,3)

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$thing is generally a serial number and is unique. In a few cases the serial number may be appended with (O) or (R). So there are 3 potential values: 
  serial
  serial(O)
  serial(R)

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second file gives me another 2 values for the list: 
  push(@$hash{$thing},4,5)

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In this file, I am getting data based on serial number, but here there is never anything appended to serial number, so I have: 
   serial

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In order to push, I am looking for the key that starts with serial 
 ^serial

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Due to the number of iterations, I am avoiding a foreach for the keys of $hash and I want to keep the (O) or (R) portion as it has significance. Can you do something like: 
 if ($hash{^$file}) { do something }

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In reply to regex of hash key on the fly by martzpet

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