if ($hash{^$file}) { do something }

##</code><code>##

  $hash{$thing} = (1,2,3)

##</code><code>##

  serial
  serial(O)
  serial(R)

##</code><code>##

  push(@$hash{$thing},4,5)

##</code><code>##

   serial

##</code><code>##

 ^serial

##</code><code>##

 if ($hash{^$file}) { do something }