diff --git a/util/strnum.c b/util/strnum.c
new file mode 100644
index 0000000..14f2f88
--- /dev/null
+++ b/util/strnum.c
@@ -0,0 +1,20 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include <stdlib.h>
+#include "../util.h"
+
+long
+strnum(const char *s, int base)
+{
+	char *end;
+	long n;
+	
+	n = strtol(s, &end, base);
+	if(*end != '\0') {
+		if(base == 0)
+			eprintf("%s: not a number\n", s);
+		else
+			eprintf("%s: not a base %d number\n", s, base);
+	}
+	return n;
+}