diff --git a/drl2gp/drl2gp.c b/drl2gp/drl2gp.c
index bd03269..dbc2d8e 100644
--- a/drl2gp/drl2gp.c
+++ b/drl2gp/drl2gp.c
@@ -36,6 +36,7 @@
 #define	MAX_STEP	0.01	/* max arc step, in mm */
 
 
+static const char *filter = NULL;
 static double tool_d[MAX_TOOL+1];
 static FILE *out = NULL;
 static int lineno = 1;
@@ -48,6 +49,9 @@ static double depth, d0, d1;
 #define	MIL2MM(mil)	IN2MM((mil)/1000)
 
 
+/* ----- gnuplot output ---------------------------------------------------- */
+
+
 static void eprintf(const char *fmt, ...)
 {
 	va_list ap;
@@ -61,6 +65,78 @@ static void eprintf(const char *fmt, ...)
 }
 
 
+static double arc2angle(double arc, double r)
+{
+	return acos(1-arc*arc/(r*r)/2);
+}
+
+
+static void half_circle(double cx, double cy, double rx, double ry, double s)
+{
+	double m[4];
+	double x = rx, y = ry, tmp;
+	double a;
+
+	m[0] = cos(s);
+	m[1] = -sin(s);
+	m[2] = -m[1];
+	m[3] = m[0];
+
+	for (a = 0; a < M_PI; a += s) {
+		eprintf("%f %f %f\n", cx+x, cy+y, -depth);
+		tmp = x*m[0]+y*m[1];
+		y = x*m[2]+y*m[3];
+		x = tmp;
+	}
+	eprintf("%f %f %f\n", cx-rx, cy-ry, -depth);
+}
+
+
+static void slot(double xa, double ya, double xb, double yb, double d)
+{
+	double dx = xb-xa;
+	double dy = yb-ya;
+	double cr = d/2;
+	double tr = d0/2;
+	double s = arc2angle(MAX_STEP, cr);
+	double nx, ny;
+	double f;
+
+	assert(mill);
+	f = (cr-tr)/hypot(dx, dy);
+	nx = -dy*f;
+	ny = dx*f;
+
+	half_circle(xa, ya, nx, ny, s);
+	half_circle(xb, yb, -nx, -ny, s);
+	eprintf("%f %f %f\n\n", xa+nx, ya+ny, -depth);
+}
+
+
+static void circle(double cx, double cy, double d)
+{
+	double cr = d/2;
+	double tr = d0/2;
+	double s = arc2angle(MAX_STEP, cr);
+	double a;
+
+	assert(mill);
+	for (a = 0; a < 2*M_PI; a += s)
+		eprintf("%f %f %f\n",
+		    cx+(cr-tr)*cos(a), cy+(cr-tr)*sin(a), -depth);
+	eprintf("%f %f %f\n\n", cx+(cr-tr), cy, -depth);
+}
+
+
+static void drill(double x, double y)
+{
+	eprintf("%f %f %f\n\n", x, y, -depth);
+}
+
+
+/* ----- header parsing ---------------------------------------------------- */
+
+
 static void header(void)
 {
 	enum {
@@ -80,7 +156,7 @@ static void header(void)
 	while ((c = getchar()) != EOF) {
 		if (out) {
 			if (fputc(c, out) == EOF) {
-				perror("write");
+				perror(filter);
 				exit(1);
 			}
 		}
@@ -178,78 +254,14 @@ static void header(void)
 }
 
 
-static double arc2angle(double arc, double r)
-{
-	return acos(1-arc*arc/(r*r)/2);
-}
+/* ----- body parsing ------------------------------------------------------ */
 
 
-static void half_circle(double cx, double cy, double rx, double ry, double s)
-{
-	double m[4];
-	double x = rx, y = ry, tmp;
-	double a;
-
-	m[0] = cos(s);
-	m[1] = -sin(s);
-	m[2] = -m[1];
-	m[3] = m[0];
-
-	for (a = 0; a < M_PI; a += s) {
-		eprintf("%f %f %f\n", cx+x, cy+y, -depth);
-		tmp = x*m[0]+y*m[1];
-		y = x*m[2]+y*m[3];
-		x = tmp;
-	}
-	eprintf("%f %f %f\n", cx-rx, cy-ry, -depth);
-}
-
-
-static void slot(double xa, double ya, double xb, double yb, double d)
-{
-	double dx = xb-xa;
-	double dy = yb-ya;
-	double cr = d/2;
-	double tr = d0/2;
-	double s = arc2angle(MAX_STEP, cr);
-	double nx, ny;
-	double f;
-
-	assert(mill);
-	f = (cr-tr)/hypot(dx, dy);
-	nx = -dy*f;
-	ny = dx*f;
-
-	half_circle(xa, ya, nx, ny, s);
-	half_circle(xb, yb, -nx, -ny, s);
-	eprintf("%f %f %f\n\n", xa+nx, ya+ny, -depth);
-}
-
-
-static void circle(double cx, double cy, double d)
-{
-	double cr = d/2;
-	double tr = d0/2;
-	double s = arc2angle(MAX_STEP, cr);
-	double a;
-
-	assert(mill);
-	for (a = 0; a < 2*M_PI; a += s)
-		eprintf("%f %f %f\n",
-		    cx+(cr-tr)*cos(a), cy+(cr-tr)*sin(a), -depth);
-	eprintf("%f %f %f\n\n", cx+(cr-tr), cy, -depth);
-}
-
-
-static void drill(double x, double y)
-{
-	eprintf("%f %f %f\n\n", x, y, -depth);
-}
+static int active = 0;
 
 
 static void do_cmd(char cmd, double v, int nl)
 {
-	static int active = 0;
 	static int metric = 1;
 	static int slotting = 0;
 	static double x = 0, y = 0, x0 = 0, d = 0;
@@ -346,6 +358,11 @@ static void body(void)
 	int c, s = 0;
 
 	while ((c = getchar()) != EOF) {
+		if (out && (c == 'T' || cmd == 'T' || !active))
+			if (fputc(c, out) == EOF) {
+				perror(filter);
+				exit(1);
+			}
 		if (c == '\n') {
 			lineno++;
 			if (cmd)
@@ -374,6 +391,9 @@ static void body(void)
 }
 
 
+/* ----- command line ------------------------------------------------------ */
+
+
 static void usage(const char *name)
 {
 	fprintf(stderr,
@@ -390,7 +410,6 @@ static void usage(const char *name)
 
 int main(int argc, char **argv)
 {
-	const char *filtered = NULL;
 	int metric = 1;
 	double arg[MAX_ARGS];
 	int n_arg = 0;
@@ -422,15 +441,15 @@ int main(int argc, char **argv)
 			metric = 1;
 			break;
 		case 'f':
-			if (filtered)
+			if (filter)
 				usage(*argv);
 			if (argv[i][2])
-				filtered = argv[i]+2;
+				filter = argv[i]+2;
 			else {
 				i++;
 				if (i == argc)
 					usage(*argv);
-				filtered = argv[i];
+				filter = argv[i];
 			}
 			break;
 		default:
@@ -454,6 +473,14 @@ int main(int argc, char **argv)
 		usage(*argv);
 	}
 
+	if (filter) {
+		out = fopen(filter, "w");
+		if (!out) {
+			perror(filter);
+			exit(1);
+		}
+	}
+
 	header();
 	body();
 
@@ -462,5 +489,10 @@ int main(int argc, char **argv)
 		exit(1);
 	}
 
+	if (filter && fclose(out) == EOF) {
+		perror(filter);
+		exit(1);
+	}
+
 	return 0;
 }