What is Make?
GNU Make is a tool which controls the generation of executables and other non-source files of a program from the program’s source files.
Make gets its knowledge of how to build your program from a file called the makefile, which lists each of the non-source files and how to compute it from other files. When you write a program, you should write a makefile for it, so that it is possible to use Make to build and install the program. (Source)
With awareness of both how to generate a file (the target) and what that file needs (its dependencies), make can help save valuable time and prevent you from having to rebuild a target whose dependencies did not change since the last build.
Although make is great at saving time, it takes some expertise to manage efficient work during code cleanup phases.
The make clean target
Most projects come with a make clean target providing a developer with the ability to remove any non-source file the make program generated. Even the reference itself instructs how to clean build output:
1 2 3 | .PHONY : clean clean : -rm edit $(objects) |
The whole Makefile might be close to:
1 2 3 4 5 6 7 8 9 10 | TARGETS=bin/prog1 all: ${TARGETS} bin/%: mkdir -p bin echo $@ > $@ clean: - rm ${TARGETS} |
It is then possible to run:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | $> make mkdir -p bin echo bin/prog1 > bin/prog1 $> ls bin prog1 $> make make: Nothing to be done for `all'. $> make clean rm bin/prog1 $> ls bin $> make mkdir -p bin echo bin/prog1 > bin/prog1 $> ls bin prog1 |
It also works when adding targets:
1 2 3 4 5 6 7 | $> make TARGETS='bin/prog1 bin/prog2 bin/prog3' # this simulates the addition of 2 new targets in Makefile mkdir -p bin echo bin/prog2 > bin/prog2 mkdir -p bin echo bin/prog3 > bin/prog3 $> ls bin prog1 prog2 prog3 |
However, when targets are removed (e.g. when you are moving outside of a feature branch adding a program), make won’t be able to clean your working directory properly:
1 2 3 4 | $> make clean rm bin/prog1 $> ls bin prog2 prog3 |
Improving the make clean target
As we noticed, our current implementation of the build is not reproducible, hence some files in the bin are still available but not rebuildable after a git clone.
To solve this issue, the first approach would be to clean the whole repository after each checkout with git clean -dxf . However this can be very inefficient if your build time is high.
Another option is to add a simple script in charge of cleaning previously buildable targets (./cleanup.sh):
1 2 3 4 5 6 7 8 9 10 11 12 13 | #!/bin/bash if [ -f .targets ] ; then for target in $(cat .targets); do if [[ "${TARGETS}" != *"${target}"* ]]; then if [ -e ${target} ]; then echo "Removing dangling target ${target}" >&2 rm ${target} fi fi done fi echo "${TARGETS}" > .targets |
integrate it in the makefile:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | TARGETS=bin/prog1 $(shell env TARGETS="${TARGETS}" ./cleanup.sh >&2) all: ${TARGETS} .PHONY: clean bin/%: mkdir -p bin echo "#/bin/bash" > $@ echo "echo $@" > $@ chmod +x $@ clean: - rm ${TARGETS} |
and test the changes:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | $> make TARGETS='bin/prog1 bin/prog2 bin/prog3' mkdir -p bin echo "#/bin/bash" > bin/prog2 echo "echo bin/prog2" > bin/prog2 chmod +x bin/prog2 mkdir -p bin echo "#/bin/bash" > bin/prog3 echo "echo bin/prog3" > bin/prog3 chmod +x bin/prog3 $> make clean Removing dangling target bin/prog2 Removing dangling target bin/prog3 rm bin/prog1 $> ls bin | wc -l 0 |
Conclusion
Whenever you’re considering performing an update either with make as described here, or with puppet, ansible or other configuration management tools, don’t forget to remove anything redundant to prevent the famous it works for me pattern.
You can find the illustrations of this article hosted on GitHub: https://github.com/leboncoin/bytes-clean-examples