It sounds as if you've got the basics already (though it's hard to tell).

my $pid = fork();
die "Can't fork: $!" if ! defined $pid;
if ( $pid ) {
    # parent
    $SIG{INT} = sub {
        warn "Sending sig INT to child PID $pid";
        kill 'INT' => $pid;
    };
    wait;
}
else {
    # child
    $SIG{INT} = sub { die "Caught sig INT" };
    sleep 1 while 1;
    exit;
}
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Note that without the signal handler in the child, it will still die when it gets the INT signal. I put it in the example just to make the signal visible.