while ($data = <$fh>) {
   # do something with $data
}
if ($fh->READLINE_ERROR) {   # but this method doesn't exist
   # handle readline error
} else {
   # handle EOF
}
[download]

perldoc readline offers something like:

while (1) {
   undef $!;   # doesn't really undefine $!
   $data = readline $fh;   # or $fh->readline
   if (!defined $data) {
      last unless $!;   # EOF
      # handle readline error
   }
   # do something with $data
}
[download]

This sort of works. In fact, if use warnings is in effect, then the readline will report an error on stderr, at least for some kind of errors, in addition to setting $!. But, more importantly, this code is kind of ugly. And if I have to trap warnings in some way, it will get even uglier. Is this really the best or only way to write robust line-at-a-time input handling?
I've found something like the following in Stein's "Network Programming with Perl":

undef $!;
while ($data = <$fh>) {
   # do something with $data
}
if (defined $!) {
   # handle readline error
}
[download]

This is almost identical to my preferred way, but seems buggy because:

1. undef $! doesn't really undefine $! because defined($!) returns true after undef($!) !!
2. if the "do something" part sets $! then this will fail
3. warnings from <readline> sent to stderr will have to be handled in some way

The Camel 3rd edition doesn't seem to mention readline errors. Surprisingly, Perl Best Practices doesn't mention readline error handling either.

What about using $fh->eof or $fh->error? They don't seem to work quite like I want to handle this case. But they don't seem to be documented well enough for me to tell for sure.