You can just replace die with the name of the sub you want to run. You can put practically any command you want after the ||. There is nothing intrinsically special about the open||die pairing, it's just a common convention used to handle errors.

sub dontdie()
{
  print "I didn't die\n";
} 

open(LOK, ">>C:\\Perl\\RTEOlock\\check\\RTEOlock.log") || dontdie();
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open(LOK, ">>C:\\Perl\\RTEOlock\\check\\RTEOlock.log") || this_is_sub(
+) ;
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unless ( open(LOK, ">>C:\\Perl\\RTEOlock\\check\\RTEOlock.log") ) {
  # do what ever we can not open the file
  ...
}
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This can be done several ways (as usual). For example:

open(LOK, ">>/non-existing/file") || my_subroutine($!);

sub my_subroutine {
   print "Oh no! Error: ".shift;
}
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Thank you for your helpful response. R_D

Can one or(||) to a subroutine instead die?

Abigail

if (!open($HANDLE, ">>filename.log")) {
    # call a sub-routine
}
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First, it's usually a good idea to use the lower-precedent version of || in instances like this. It is spelled or. This allows you (or perhaps some poor maintenance programmer) to remove the ()'s around open's arguments without making bad things happen.

Second, what did you try? What's the obvious and simple answer? It's quite easy:

Update: I guess I should refresh my browser tabs more often. I'm not quite sure how I managed to reply an hour later without noticing other replies saying the same thing. :)

There's nothing special about die being the right operand of ||. You can use any expression there; it will be evaluated in scalar context. Personally, I prefer the spelled out, low-precedence or for things like this.