$! = 0;
$line = <$file>;
if (!defined($line) && $!)
        { die "error readline: $!"; }
elsif (!defined($line))
        { print "reached eof\n"; }
else
        { $line=~/(.*)/; print qq(read a line: "$1"); }

##</code><code>##

echo $'three\nshort\nlines' > a;
 perl -we 'open $f, "<", "a"; for(0..3) { $!=10000; $l = <$f>; $s = $!; warn +(defined($l)?$l=~/(.*)/&&qq/"$1"/:"undef"), " $s\n"; }'

##</code><code>##

"three" Bad file descriptor
"short" Unknown error 10000
"lines" Unknown error 10000
undef 
undef