This module allows an application to use cexpsh() instead
of iocsh from 'main'. It also adds entry points to iocsh
so that cexpsh may be called from iocsh.

Currently relevant and supported on Linux only.

To use this module:

   - add and entry in your application's RELEASE file pointing
     to this module.

   - your application's 'main' may look like this:

       #include <iocsh.h>
       #include <epicsThread.h>
       #include <epicsExit.h>

       #ifdef HAVE_CEXP
       #include <cexp.h>
       #endif

       int
       main(int argc, char **argv)
       {
       #ifdef HAVE_CEXP
         cexp_main(argc, argv);
       #else
         if ( argc >= 2 ) {
           iocsh(argv[1]);
           epicsThreadSleep(0.2);
         }
         iocsh(NULL);
       #endif
         epicsExit();
         return 0;
       }

     Some makefile magic provided by this module automatically
     defines HAVE_CEXP on platforms where cexpsh is available.

     Note that it is not mandatory to start cexpsh from 'main'.
     cexpsh can also be called from iocsh at run-time.

   - Your application's Makefile must link the cexp (and dependent)
     libraries. Again, the makefile magic defines CEXP_LIBS only
     when applicable:

         <myApp>_LIBS += $(CEXP_LIBS)

     Your application's Makefile must also include this module's
     'dbd' file:

         <myApp>_DBD  += $(CEXP_DBDS)

NOTES:
   1 No special symbol table is built - hence only symbols defined
     by the main application and/or shared libraries linked by the
     main application are 'known' to the shell.
     Your application's Makefile may enforce linking symbols from
     non-shared libraries which are not referenced by your app by
     adding

         -Wl,-u,<symbol>

     to the linker flags.

   2 cexp now supports reading symbols from shared libraries. All
     global symbols exported by any shared libs used by the
     application are available.

   3 This module registers cexpsh with iocsh so that it may be
     called from the latter:

         cexpsh()

     Invokes cexpsh in interactive mode which may be terminated
     by typing '<CTRL>-D'. You may also supply arguments in which
     case cexpsh() returns to iocsh immediately after executing:

         iocsh> cexpsh("-c",'printf("hello\n")')
     

BUILDING THIS MODULE
====================

In order to build this module you must install the CEXP
sources in a subdirectory of $(TOP)/cexp/<subdir> and define

CEXP_VERS=<subdir>

in $(TOP)/configure/CONFIG_SITE accordingly. CONFIG_SITE
also defines

CEXP_SRCDIR=$(TOP)/cexp/$(CEXP_VERS)

which you may modify if you choose to install the CEXP
sources elsewhere.

If you are working with a CVS checkout of CEXP then the
package must be prepared:

  chdir $(TOP)/cexp/<subdir>
  make prep

This requires 'bison' and recent autotools.

A released tarball of CEXP does not need this preparation 
step.

If you want disassembler support then you have to install
binutils sources (vers. 2.21 works) and create a symlink
from the cexp top source directory to the binutils sources.

ln -s <binutils-2.21-top>  cexp/$(CEXP_VERS)/binutils

After installing the sources, chdir to $(TOP) and issue
'make' as usual (make clean is required if you had
already built before installing binutils).