diff --git a/gencat/Makefile b/gencat/Makefile
index d4efcc0..1f31e21 100644
--- a/gencat/Makefile
+++ b/gencat/Makefile
@@ -11,7 +11,7 @@
 
 PREFIX ?= /usr/local
 
-OBJS = gencat.o tree.o libs.o comp.o pdf.o
+OBJS = gencat.o tree.o libs.o run.o comp.o pdf.o
 
 SHELL = /bin/bash
 CFLAGS = -Wall -g
diff --git a/gencat/pdf.c b/gencat/pdf.c
index e4da63a..ea79308 100644
--- a/gencat/pdf.c
+++ b/gencat/pdf.c
@@ -9,16 +9,15 @@
  * (at your option) any later version.
  */
 
-#define	_GNU_SOURCE
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
-#include <sys/types.h>
 
 #include "util.h"
 #include "gencat.h"
 #include "tree.h"
 #include "libs.h"
+#include "run.h"
 #include "pdf.h"
 
 
@@ -279,39 +278,9 @@ static void print_comment(FILE *file, const struct line *comment)
 /* ----- Component conversion ---------------------------------------------- */
 
 
-static void cat(FILE *out, const char *name)
-{
-	FILE *in;
-	char buf[10000]; /* pick any good size */
-	size_t got, wrote;
-
-	in = fopen(name, "r");
-	if (!in) {
-		perror(name);
-		exit(1);
-	}
-	while (1) {
-		got = fread(buf, 1, sizeof(buf), in);
-		if (!got)
-			break;
-		wrote = fwrite(buf, 1, got, out);
-		if (wrote != got) {
-			perror("fwrite");
-			exit(1);
-		}
-	}
-	if (ferror(in)) {
-		perror(name);
-		exit(1);
-	}
-	fclose(in);
-}
-
-
 static void convert_comp(const struct node *node, FILE *out)
 {
-	char *tmp;
-	int i, res;
+	int i;
 
 	for (i = 0; i != node->e->units; i++) {
 		if (!quiet) {
@@ -321,21 +290,9 @@ static void convert_comp(const struct node *node, FILE *out)
 		make_title(out, node, i);
 		if (!i && node->comment)
 			print_comment(out, node->comment);
-		if (asprintf(&tmp, "sym2xps '%s' '%s' %d '%s' '%s'", 
+		run_cmd("sym2xps '%s' '%s' %d '%s' '%s'", 
 		    node->e->file->path, node->e->names->s, i+1,
-		    "tmp", "tmp.ps") < 0) {
-			perror("asprintf");
-			exit(1);
-		}
-		res = system(tmp);
-		if (res < 0) {
-			perror("system");
-			exit(1);
-		}
-		if (res) {
-			fprintf(stderr, "sym2xps returned %d\n", res);
-			exit(1);
-		}
+		    "tmp", "tmp.ps");
 		fprintf(out, "gsave %s\n", format.comp_setup);
 		cat(out, "tmp.ps");
 		fprintf(out, "\ngrestore\n");
diff --git a/gencat/run.c b/gencat/run.c
new file mode 100644
index 0000000..ba9acc4
--- /dev/null
+++ b/gencat/run.c
@@ -0,0 +1,70 @@
+/*
+ * run.c - Run helper scripts
+ *
+ * Copyright 2012 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#define _GNU_SOURCE /* for vasprintf */
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/types.h>
+
+#include "run.h"
+
+
+void run_cmd(const char *fmt, ...)
+{
+	va_list ap;
+	char *tmp;
+	int res;
+
+	va_start(ap, fmt);
+	if (vasprintf(&tmp, fmt, ap) < 0) {
+		perror("vasprintf");
+		exit(1);
+	}
+	res = system(tmp);
+	if (res < 0) {
+		perror("system");
+		exit(1);
+	}
+	if (res) {
+		fprintf(stderr, "sym2xps returned %d\n", res);
+		exit(1);
+	}
+}
+
+
+void cat(FILE *out, const char *name)
+{
+	FILE *in;
+	char buf[10000]; /* pick any good size */
+	size_t got, wrote;
+
+	in = fopen(name, "r");
+	if (!in) {
+		perror(name);
+		exit(1);
+	}
+	while (1) {
+		got = fread(buf, 1, sizeof(buf), in);
+		if (!got)
+			break;
+		wrote = fwrite(buf, 1, got, out);
+		if (wrote != got) {
+			perror("fwrite");
+			exit(1);
+		}
+	}
+	if (ferror(in)) {
+		perror(name);
+		exit(1);
+	}
+	fclose(in);
+}
diff --git a/gencat/run.h b/gencat/run.h
new file mode 100644
index 0000000..09e348b
--- /dev/null
+++ b/gencat/run.h
@@ -0,0 +1,18 @@
+/*
+ * run.h - Run helper scripts
+ *
+ * Copyright 2012 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef RUN_H
+#define RUN_H
+
+void run_cmd(const char *fmt, ...);
+void cat(FILE *out, const char *name);
+
+#endif /* !RUN_H */