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

##</code><code>##

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
}

##</code><code>##

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