sub f {
   my $pos = tell(DATA);
   while (<DATA>) {  # Assigns to $_, but $_ is aliased to 1.
      print;
   }
   seek(DATA, $pos, 0);
}

# sub f {
#    my $pos = tell(DATA);
#    while (defined(my $line = <DATA>)) {
#       print $line;
#    }
#    seek(DATA, $pos, 0);
# }

f() for 1,2,3;

__DATA__
a
b
c