When you write while ($scalar = <FILEHANDLE>) { ... }, perl takes care of the test for definedness for you:

$ perl -MO=Deparse -e 'open $fh,"foo.txt"; while (my $line = <$fh>) { 
+print $line }'
open $fh, 'foo.txt';
while (defined(my $line = <$fh>)) {
    print $line;
}
-e syntax OK
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