perl is complaining about your while-test. You have to test with defined, like this: while( defined($_ = <>) && $_ ne "quit\n" ) {} The reason, as stated in the error message, is because the <> may generate a "0", and that would evaluate to false. With defined however, it will evaluate to true.

Newer perls usually puts the defined() around any such simple constructs as $_ = <SOME_HANDLE>. (within a while). Take this as an example:

perl -MO=Deparse -le 'while($_ = <>) {}'
-e syntax OK

while (defined($_ = <ARGV>)) {
    ();
}
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However, this is not done with more complicated constructs such as yours.

Autark.