AFAIK, IO::Socket::INET->new() does not set $!,

Quite the opposite. It's the only module I know that does set $! even for errors not originating from system calls. That could account for the error message mismatch.

Well, if it does, I can't find any mention of that behaviour in the documentation. The only thing that I can find that even mentions $! is IO::Handle's blocking() method.

update: however, reading the source code shows that you're right. But I can't really say if it will always produce a useful error in $! though. Sometimes it sets $! to $EINVAL, other times it just passes on $! from functions that may or may not set $! on failure. (And some build in functions that do set $! are not documented as such in the perldocs, but that's another story)

"What should it profit a man, if he should win a flame war, yet lose his cool?"

AFAIK, IO::Socket::INET->new() does not set $!

It's poorly documented, but IO::Socket and its INET subclass put their informative errors into $@. So, the OP wants something like:

  my $s = IO::Socket::INET->new(...) or die "new sock: $@\n";
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-pilcrow