--- /dev/null
+#!/usr/bin/perl
+
+use strict;
+my $fn = shift @ARGV;
+my $old = `cat $fn`;
+my $header = `cat doc/modeline.txt`;
+
+# strip existing modeline
+my $new = $old;
+$new =~ s/^\/\/ \-\*\- ([^\n]+) \-\*\-([^\n]*)\n//s; # emacs
+$new =~ s/^\/\/ vim: ([^\n]*)\n//s; # vim;
+$new =~ s/^\/\/ \-\*\- ([^\n]+) \-\*\-([^\n]*)\n//s; # emacs
+$new =~ s/^\/\/ vim: ([^\n]*)\n//s; # vim;
+$new =~ s/^\/\/ \-\*\- ([^\n]+) \-\*\-([^\n]*)\n//s; # emacs
+$new =~ s/^\/\/ vim: ([^\n]*)\n//s; # vim;
+
+# add correct header
+$new = $header . $new;
+
+if ($new ne $old) {
+ print "$fn\n";
+ open(O, ">$fn.new");
+ print O $new;
+ close O;
+ system "diff $fn $fn.new";
+ rename "$fn.new", $fn;
+ #unlink "$fn.new";
+}
+