You have a few errors in the code you're trying.

1. You need to wrap the code that might time out in an eval.
2. The die $@ if $@ && $@ !~ /alarm timeout/; has to come after the eval.
3. It's recommended, when throwing your own exceptions, to end the string in a newline, e.g. die "timeout\n".

# example
{
    # this scope is here just to localize the signal handler

    local $SIG{ALRM} = sub { die "timeout\n" };
    alarm $TIMEOUT;

    eval {
        # iffy code

        1;
    } or do {
        die $@ unless $@ eq "timeout\n"; # propagate other exceptions

        # handle timeout
    };
    alarm 0; # free alarm
}
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