-open PLIN, "patchlevel.h" or die "Couldn't open patchlevel.h : $!";
-open PLOUT, ">patchlevel.new" or die "Couldn't write on patchlevel.new : $!";
+open PLIN, "<", "patchlevel.h" or die "Couldn't open patchlevel.h : $!";
+open PLOUT, ">", "patchlevel.new" or die "Couldn't write on patchlevel.new : $!";