Create "If Different" dependency

[Yair Lenga]

Hi,

I have to setup a makefile rules that will update the target if the source is different from the target. Ideally, I will write

target: source
cp $< $@

Unfortunanly, this does not work for me. First, the target might be modified by other processes. The other problem is that the "make" is being executed on different machines, which may have "time drift" - making timestamps fail sometimes. My best solution is:

.PHONY: FORCE

target: FORCE
cmp -s source target || cp source $@

This approach takes a lot of CPU, and network bandwidth (I'm using NFS). Does anyone has better solution ? Some packages offer MD5 instead/in addition to timestamping. Can this appraoch be applied with gnu-make ?

Thanks
Yair Lenga




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