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Using Gperf with the GNU Build System

Currently neither Autoconf nor Automake provide direct Gperf support, but interfacing Gperf with them is straightforward.

All needs to do is to look for gperf and to provide its definition for Makefiles via AC_SUBST Autoconf (FIXME: ref Autoconf.). In fact, using Automake's macro to put gperf under the control of missing is enough:

     AM_MISSING_PROG([GPERF], [gperf])

Then your should include:

     # Handling the Gperf code
     GPERFFLAGS = --compare-strncmp --switch=1 --language=ANSI-C
     BUILT_SOURCES = atoms.c
     atoms.c: atoms.gperf
             if $(GPERF) $(GPERFFLAGS) --key-positions=1,3,4 --struct-type \
                atoms.gperf >$@t; then \
               mv $@t $@; \
             elif $(GPERF) --version >/dev/null 2>&1; then \
               rm $@t; \
               exit 1; \
             else \
               rm $@t; \
               touch $@; \

I personally avoid using short options in scripts and Makefiles, because short options are likely to change and because long options are easier to understand when you don't know the program. Do not forget to help Automake understand that atoms.c is to be built early (before its uses) using BUILT_SOURCES.

The program gperf is a maintainer requirement: someone changing the package needs it, but its result is shipped so that a regular user does not need it. Hence, we go through some hoops in order to ensure that a failed run of gperf doesn't erase the maintainer's pre-built copy of atoms.c. Had gperf provided an --output option, missing would have handled these details gracefully.

There are three cases to handle:

gperf succeeded
Then just rename the temporary output file, @t, as the actual output, @;
gperf failed
If the $(GPERF) invocation failed, but $(GPERF) --version succeeded, then this is certainly an actual error in the input file. In this case, do not hide the failure and exit with failure.
gperf is missing
If $(GPERF) does not answer to --version, it is certainly missing, and missing already suggested to install Gperf. Then remove the temporary output file, and let the compilation proceed by updating the timestamp of the output file. That's a best effort, essentially helping users who get the project with broken timestamps.