#!/usr/bin/perl
 
 # Simple ifdef/else/endif processor.
 
 die "usage: ifdef [-C<command-prefix>] [-Dname ...] [control-file ...] " if (@ARGV[0] =~ /^(-h|--help)$/);
 
 %Parms = ();
 
 $pre = "!";
 while ($arg=shift(@ARGV)) {
     if ($arg =~ /^-/) {
 	if ($arg =~ /^-D(\w+)$/) {
 	    $Parms{$1} = 1;
 	} elsif ($arg =~ /-C(.*)$/) {
 	  $pre = $1;
 	} else {
 	    die "unrecognized option: $arg";
 	}
     } else {
 	open(CONTROL, "< $arg") or die "cannot open $arg";
 	while (<CONTROL>) {
 	    if (/^!define\s+(\w+)/) {
                 $Parms{$1} = 1;
             }
         }
     }
 }
 
 sub ifdef {
   my ($var, $enabled) = @_;
   my $def = 0;
   $def = 1 if (defined $Parms{$var}) || ($var eq "true");
   $def = 0 if $var eq "false";
   while (<STDIN>) {
     if (/^\s*\Q$pre\Eifdef\s+(\w+)\s*$/) {
       return 1 if ifdef ($1, $def & $enabled);
     } elsif (/^\s*\Q$pre\Eelseif\s+(\w+)\s*$/) {
       $def = $def ^ 1;
       return ifdef ($1, $def & $enabled);
     } elsif (/^\s*\Q$pre\Eelse\s*$/) {
       $def = $def ^ 1;
     } elsif (/^\s*\Q$pre\Eendif\s*$/) {
       return 0;
     } elsif (/^\s*\Q$pre\E/) {
       die "unrecognized command: $_";
     } else {
       print if $def && $enabled;
     }
   }
   return 1;
 }
 
 ifdef("true", 1);