I second the recommendation to use exception instead of goto and to reset the alarm afterwards.

Personally, I prefer to have the signal handler and alarm calls enclosed inside the eval as well - to me, it's more obvious what's going on that way. alarm and perlipc show the same approach:

eval {
    local $SIG{ALRM} = sub { die "timeout" };
    alarm 10;
    $input = <STDIN>;
    alarm 0;
};
if ($@ and $@ =~ /timeout/) { 
    print "Reading timed out";
} elsif ($@) {
    die "Other error: $@";
}
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