Automake stops with “non-POSIX variable name”

I created a Makefile.in where I read the content out of a file and pass it to CFLAGS. Calling ./configure ... the Makefile will be generated an all works well.

Makefile.in: 
... 
MY_REVISION_FILE=my-revision.txt 
MY_REVISION=$(shell cat $(top_srcdir)/$(MY_REVISION_FILE)) 
AM_CFLAGS = -I$(EXTRAS_INCLUDE_DIR) -I$(top_srcdir) -DMY_REVISION=$(MY_REVISION) 
... 

The problem arises once I moved the Makefile.in code into Makefile.am to allow the auto generation of Makefile.in. There calling autoreconf -i --force stops with the following error:

server/Makefile.am:9: cat $(top_srcdir: non-POSIX variable name 
server/Makefile.am:9: (probably a GNU make extension) 
autoreconf: automake failed with exit status: 1 

This problem hunts me now since quite some time. I searched everywhere but did not find anything that could help me finding a solution for that. In short, the only thing I need is a way to get an uninterpreted text such as "$(shell cat $(top_srcdir)/$(MY_REVISION_FILE))" copied from Makefile.am to Makefile.in

Any idea?

Thanks, Oliver

After long testing back and forth I decided to use AC_SUBST. My solution might not be the cleanest but it works for me.

In configure.ac I added the following line AC_SUBST([DOLLAR_SIGN],[$])

In the Makefile.am I changed my previous line into MY_REVISION=@DOLLAR_SIGN@(shell cat $(SRC_DIR)/$(MY_REVISION_FILE))

And it works. Again, thanks for your help.