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       eof FILEHANDLE
       eof ()
...
               "eof(FILEHANDLE)" on it) after end-of-file is
               reached.  File types such as terminals may lose
               the end-of-file condition if you do.

               Practical hint: you almost never need to use "eof"
               in Perl, because the input operators typically
               return "undef" when they run out of data, or if
               there was an error.

while (<STDIN>) {
    print;
    print "***\n";
}

while (<STDIN>) {
    print $_, "***\n";
}