Makefile % match-anything 规则选择“Makefile”目标

Question

I'm trying to write a universal Makefile to sync the source tree with some remote host, ssh into it and execute make there, forwarding any targets or variable overrides

So far I came up with this:

HOST ?= host
DIR ?= ~/dev

SRC = src

all:

.PHONY: sync
sync:
    rsync -azP --exclude ".*/" --exclude ".*" $(SRC)/ $(HOST):$(DIR)

%: sync
    ssh $(HOST) 'cd $(DIR) && make $@ MAKEFLAGS=$(MAKEFLAGS)'

It works great as long as I omit sync in the dependency list of % target. Once I add it back in, Makefile target is picked up for some reason, causing it to ssh into the remote machine and run make Makefile , which is not a valid target or expected behaviour

To clarify, I don't specify Makefile as a target myself. I do

make
make clean

All of which result in Makefile target being run regardless

Answer 1

GNU make automatically attempts to rebuild the makefile(s) before building the designated targets or default target . Other make implementations do not necessarily do this. The GNU make manual contains this advice about your particular problem:

If you know that one or more of your makefiles cannot be remade and you want to keep make from performing an implicit rule search on them, perhaps for efficiency reasons, you can use any normal method of preventing implicit rule look-up to do so. For example, you can write an explicit rule with the makefile as the target, and an empty recipe [...]

The empty recipe approach would be to add a rule such as this:

Makefile: ;

With that present in your makefile (and the file's name being Makefile ), when make looks for a rule with which to rebuild Makefile it will choose that explicit, empty rule instead of the match-anything wildcard rule. It would be a little more robust to write that like this, however:

$(MAKEFILE_LIST): ;

The MAKEFILE_LIST variable contains the names of all the makefiles that make read, so it will cover you even if you add include directives to your makefile or if you access it from a different directory or via a different name by use of the -f command-line option.