Are you asking me about just the syntax? or about signal handling with %SIG ?

As far as the syntax goes, my code is equivalent to something like this:

   my $coderef = sub{ .... };
   ## now $coderef is a reference to a subroutine,
   ## which can be executed like this:
   ##
   ##    $coderef->(); # $coderef->( @args )
   ##

   $SIG{ CHLD }= $coderef;
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So that means you can actually create an anonymous subroutine, and assign it to a scalar. Which in turn can be assigned to a hash value :)

As for the signal handling portion, perldoc perlipc will give you more information. Not sure what is the best resource for that... ( I could try to explain, but I'm not confident that my knowledge is 100% correct )