sub has_header {
        my $headername = shift;
        my $dir;
	my $basepath = '/sw';
 
        if ($headername =~ /^\//) {
                return (-f $headername);
        } else {
                for $dir ('/usr/X11R6/include', $basepath . '/include', '/usr/include') {
                        return 1 if (-f $dir . '/' . $headername);
                }
        }
        return;
}
 
if ( has_header('X11/Xlib.h') ) {
    print "Found X11/Xlib.h\n";
} else {
    print "Not found X11/Xlib.h\n";
}