Question

I’m trying to use the linux utility make in order to

1. Run a script to generate the data
2. Take all of the output files (data1.txt to data79.txt) and run a script to plot them each
3. Take all those images and make a movie from them

Yes, I realize that doing this in a shell/python script would be downright simple but I’m trying to learn how to use make in this context to do the work more intelligently.

My current make file looks something like this but is significantly flawed:

movie: data *.png 
    ffmpeg data_%d.png output.mp4

%.png: %.txt
    python plot.py $< $@

data:
    python make_data.py

Answer 1

You have several problems, so let’s take them in order. (Caveats: I use GNUMake, so I can’t promise my solution will work with other flavors, and I am not familiar with ffmpeg.)

1. The data rule looks correct, but you might want to warn Make that this rule does not actually produce a file called “data”:

   .PHONY: data
   

   You can test this rule by itself: “make data”.

2. The %.png rule looks correct. You can test it: “make data26.png” (after making sure that data26.txt exists).
3. The movie rule. This is a problem, because you’re using “*.png” to indicate all png files, but at the time you run the rule there are no such files, so this evaluates to nothing. So we must look at all the data files that exist, and translate that list into a list of images to be made:

   dfiles = $(wildcard *.txt)
   images = $(dfiles:txt=png)
   

   This will work if the data files already exist (and you can test it after “make data”), but when we first run make, the data files don’t exist. There are several ways to address this; the simplest is to run Make a second time from within a rule, after the data files have been made:

       $(MAKE) output.mp4
   

Putting it all together, we get something like this:

.PHONY: movie
movie: data
    @$(MAKE) -s output.mp4 # I added the "@" and "-s" to make it quieter.

dfiles = $(wildcard *.txt)
images = $(dfiles:txt=png)

output.mp4: $(images)
    ffmpeg data_%d.png $@ 

%.png: %.txt 
    python plot.py $&lt $@ 

.PHONY: data
data: 
    python make_data.py

(Note that some people like to put all the PHONY declarations together: “.PHONY: movie data”. I prefer to do it as above.)