Cutting a string after occurrence of sub-string in a Makefile

I am writing a Makefile which needs to figure out the directory of an installed program, which can be found in PATH; or that is to say, is assumed to be in PATH.

For example: if the binary is /opt/Xilinx/12.1/ISE_DS/ISE/bin/lin64/xst, then the path I am looking for is /opt/Xilinx/12.1/ISE_DS/ISE. The program could also be found as /home/markus/Xilinx/10.1/ISE/bin/lin64/xst开发者_高级运维 for example. Xilinx included the ISE_DS part of the path only in later versions.

As a matter of fact the /bin/lin64/xst substring cannot simply be deleted, because it could also be /bin/lin/xst depending on your installation.

The Makefile could do something like XILINX_PATH = $(shell which xst) and then process this string according to the above example, but I cannot figure out how to do this in a clean way.

The best I could come up with is this:

XILINX_PATH_1 = $(shell which xst)
XILINX_PATH_2 = $(subst /bin/lin64/xst,,${XILINX_PATH_1})
XILINX_PATH = $(subst /bin/lin/xst,,${XILINX_PATH_2})

Is there a better solution?

---

This seems to work:

XILINX_PATH = $(shell which xst | sed 's%bin\/lin\(64\)*/xst%%')

Note that the * really ought to be ? for the sake of tidiness, but I'm having trouble getting that to work. I'll do a few more experiments and post an update if I solve it.

EDIT:
Using \? instead of * works on non-obsolete versions of GNUMAKE (or at least on 3.81) and is more correct.