Automation and Make

Dependencies on data and code

Learning Objectives

• Output files are a product not only of input files but of the scripts or code that created the output files.
• Recognise and avoid false dependencies.

Our Makefile now looks like this:

# Count words.
.PHONY : dats
dats : isles.dat abyss.dat last.dat

isles.dat : books/isles.txt
    python wordcount.py $< $@

abyss.dat : books/abyss.txt
    python wordcount.py $< $@

last.dat : books/last.txt
    python wordcount.py $< $@

# Generate archive file.
analysis.tar.gz : *.dat
    tar -czf $@ $^

.PHONY : clean
clean :
        rm -f *.dat
        rm -f analysis.tar.gz

Our data files are a product not only of our text files but the script, wordcount.py, that processes the text files and creates the data files. We should add wordcount.py as a dependency of each of our data files also:

isles.dat : books/isles.txt wordcount.py
    python wordcount.py $< $@

abyss.dat : books/abyss.txt wordcount.py
    python wordcount.py $< $@

last.dat : books/last.txt wordcount.py
    python wordcount.py $< $@

If we pretend to edit wordcount.py and re-run Make,

$ touch wordcount.py
$ make dats

then we get:

python wordcount.py books/isles.txt isles.dat
python wordcount.py books/abyss.txt abyss.dat
python wordcount.py books/last.txt last.dat

The following figure shows the dependencies embodied within our Makefile, involved in building the analysis.tar.gz target, after adding wordcount.py as a dependency to the .dat files:

Let’s add our analysis script to the archive too:

analysis.tar.gz : *.dat wordcount.py
        tar -czf $@ $^

If we re-run Make,

$ make analysis.tar.gz

then we get:

tar -czf analysis.tar.gz abyss.dat isles.dat last.dat wordcount.py