Question

I am confused at the following:

<>; print;

vs.

while(<>){print;}

The first one does not print anything, but second one does. Doesn’t <> always store the input read into $_?

Thank you.

Answer 1

The diamond file input iterator is only magical when it is in the conditional of a while loop:

$ perl -MO=Deparse -e '<>; print;'
<ARGV>;
print $_;
-e syntax OK

$ perl -MO=Deparse -e 'while (<>) {print;}'
while (defined($_ = <ARGV>)) {
    print $_;
}
-e syntax OK

This is all documented in perlop