Listing 1. Extract from a chip design project Makefile showing how
regression happens. The %.txt reference data is generated automatically
using C and AWK.

TESTS = test1 test2 test3 test4
.PHONY:default
default: $(TESTS:%=%.log)
        -hostname -f
        -cat $(TESTS:%=%.log)

%: %.vl
        iverilog -o$* $<
%.vl: %.v
        ./Makefile.sh $^ > $@
test1.vl: source5.v source7.v

%.log: Makefile %.txt %.out
        ls --full-time $*.out > $@
        diff -b -C2 $*.txt $*.out >> $@
        echo "... PASS ..." >> $@

.PRECIOUS: %.out %.txt
%.out: %
        time ./$* > $@
.PHONY: %.batch batch
%.batch: %
        echo "make $*.log" | batch -m
batch%: $(TESTS)
        echo "make -l $*.5" | batch -m