Add str_cut_until()

common.c

@@ -65,6 +65,12 @@ transform_str (char *s, int (*tolower) (int c))
 		*s = tolower (*s);
 }
 
+static char *
+str_cut_until (const char *s, const char *alphabet)
+{
+	return xstrndup (s, strcspn (s, alphabet));
+}
+
 static void
 split_str (const char *s, char delimiter, struct str_vector *out)
 {