dumb "build system" in 10 lines of posix sh

build.dumb

#!/usr/bin/env dumb

input fentry.cpp count.hpp
output fentry.o
cmd clang++ -std=c++17 -ggdb3 -fPIC -mgeneral-regs-only -c fentry.cpp

input count.cpp count.hpp
output count.o
cmd clang++ -std=c++17 -ggdb3 -fPIC -c count.cpp

input count.o fentry.o
output count.so
cmd clang++ -std=c++17 -ggdb3 -fPIC -shared -fvisibility=hidden count.o fentry.o -o count.so

input user.cpp
output user
cmd clang++ -std=c++17 -ggdb3 -pg -mfentry user.cpp -o user -fsanitize=address

dumb

#!/bin/sh -f
input() { in=$*; }
output() { out=; for i do out="$out -o -newer $i"; done; }
cmd() {
    if ! find -L $in -prune \( ${out# -o } \) -exec false {} + 2>/dev/null; then
        echo cmd: $@ >&2
        $@ || { e=$?; rm -f $out; exit $e; }
    fi
}
for i in ${@-./build.dumb}; do . $i; done