Index: trunk/src/hid_cam.c
===================================================================
--- trunk/src/hid_cam.c	(revision 23630)
+++ trunk/src/hid_cam.c	(revision 23631)
@@ -37,6 +37,8 @@
 #include "layer_vis.h"
 #include "plug_io.h"
 
+char *pcb_cam_base = NULL;
+
 char *pcb_layer_to_file_name(char *dest, pcb_layer_id_t lid, unsigned int flags, const char *purpose, int purpi, pcb_file_name_style_t style)
 {
 	const pcb_virt_layer_t *v;
@@ -482,6 +484,10 @@
 		else if (ctx->vl != NULL)
 			gds_append_str(s, ctx->vl->name);
 	}
+	if (strncmp(*input, "base%", 5) == 0) {
+		(*input) += 5;
+		gds_append_str(s, pcb_cam_base == NULL ? "unspecifiedbase" : pcb_cam_base);
+	}
 	else if (strncmp(*input, "top_offs", 8) == 0) {
 		int tune, from_top = -1;
 		pcb_layergrp_t *tcop = pcb_get_grp(&PCB->LayerGroups, PCB_LYT_TOP, PCB_LYT_COPPER);
Index: trunk/src/hid_cam.h
===================================================================
--- trunk/src/hid_cam.h	(revision 23630)
+++ trunk/src/hid_cam.h	(revision 23631)
@@ -27,6 +27,8 @@
 	int exported_grps;
 } pcb_cam_t;
 
+extern char *pcb_cam_base; /* substitute %base% with this */
+
 int pcb_cam_begin(pcb_board_t *pcb, pcb_cam_t *dst, const char *src, const pcb_hid_attribute_t *attr_tbl, int numa, pcb_hid_attr_val_t *options);
 
 /* Finish cam export, free all memory, mark cam export inactive and report