enable_watch is not documented to return anything or to set $!. Peeking inside the source, it appears that it intentionally returns undef on error, and only on error. However, the error message is a not stored in $! It is accessible via $c->error(). 

$c->enable_watch($host)
    or die("Can't enable watch of $host: ", $c->error(), "\n");

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In reply to Re: Problem with enable_watch by ikegami
in thread Problem with enable_watch by tayun

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