Using Make to parallelise a task

| make

I needed to run a CPU intensive script over a directory of files. Each file would be run independently, and I was using bash to achieve this:

for $i in *.txt; do ./script $i; done

This works fine, however, I have a quad core machine, and this task was CPU bound on one core. So I thought about parallelising this task so the script would run on four files at once. I didn’t want to get into the nitty gritty of changing the script to cope in this way, so instead, I “abused” Make to do this.

I created a file named “Makefile” with the following:

FILES=$(shell ls *.txt)

#default target of everything
all: $(FILES)

$(FILES):
	./script $@

.PHONY: all $(FILES)

then you just run make -j4, and four instances of the script will start running, with the concurrency being handled by Make. You can also now type make a.txt b.txt c.txt and it’ll just run the script on those three files.

You can also extend this Makefile to handle dependencies, such as running a script before all the others. Make is pretty powerful, and should be considered for more than just compiling programs.

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