Ok, this one has me entirely confused. Although I have a workaround (see below), the reason I even need a workaround escapes me.

The requirement is to be able to allow users to interrupt a certain operation (Ctrl-C) which may be called from an application that has $SIG{INT} set to 'IGNORE'. The initial code for this (Perl 5.8.8, Linux) was:

   my $intr = 0;
   my $save_handler = $SIG{INT};
   $SIG{INT} = sub { $intr++ };

   # do something here ...

   $SIG{INT} = $save_handler;

   # check value of $intr to see if I was interrupted...

[download]

What I found was that the code worked properly when $SIG{INT} had been blocked, but if called from code that did not alter $SIG{INT}, I got slammed with a "Use of uninitialized value in scalar assignment" warning.

Since I want my code to run clean, I did some investigation. First, the key INT exists, and has an undefined value. But I get the warning when I try to assign an undefined value back into the hash.

I can avoid the assignment by using a local $SIG{INT}, e.g.:

   my $intr = 0;
   {
      local $SIG{INT};
      $SIG{INT} = sub { $intr++ };

      # do something here ...

   } # end of scope for local handler

   # check value of $intr to see if I was interrupted...

[download]

... but this seems entirely bogus. Can someone suggest a good reason why %SIG would be initialized with values that I can't assign to it? I don't get this warning when I do a simple "$foo{INT} = undef;"

In reply to can't assign signal handler an undef value by papidave

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