Exercises - Make

Our Makefile currently reads as follows:

.PHONY: all clean help settings

COUNT=bin/countwords.py
COLLATE=bin/collate.py
PLOT=bin/plotcounts.py
DATA=$(wildcard data/*.txt)
RESULTS=$(patsubst data/%.txt,results/%.csv,$(DATA))

## all : regenerate all results.
all : results/collated.png

## results/collated.png: plot the collated results.
results/collated.png : results/collated.csv
	python $(PLOT) $< --outfile $@

## results/collated.csv : collate all results.
results/collated.csv : $(RESULTS) $(COLLATE)
	@mkdir -p results
	python $(COLLATE) $(RESULTS) > $@

## results/%.csv : regenerate result for any book.
results/%.csv : data/%.txt $(COUNT)
	python $(COUNT) $< > $@

## clean : remove all generated files.
clean :
	rm $(RESULTS) results/collated.csv results/collated.png

## settings : show variables' values.
settings :
	@echo COUNT: $(COUNT)
	@echo DATA: $(DATA)
	@echo RESULTS: $(RESULTS)
	@echo COLLATE: $(COLLATE)
	@echo PLOT: $(PLOT)

## help : show this message.
help :
	@grep '^##' ./Makefile

A number of the exercises below ask you to make further edits to Makefile.

1) Report results that would change

How can you get make to show the commands it would run without actually running them? (Hint: look at the manual page.)

2) Useful options

1. What does Make’s -B option do and when is it useful?

2. What about the -C option?

3. What about the -f option?

3) Make sure the output directory exists

One of our build recipes includes mkdir -p. What does this do and why is it useful?

4) Print the title and author

The build rule for regenerating the result for any book is currently:

## results/%.csv : regenerate result for any book.
results/%.csv : data/%.txt $(COUNT)
	python $(COUNT) $< > $@

Add an extra line to the recipe that uses the book_summary.sh script to print the title and author of the book to the screen. Use @bash so that the command itself isn’t printed to the screen and don’t forget to update the settings build rule to include the book_summary.sh script.

If you’ve successfully made those changes, you should get the following output for Dracula:

$ make -B results/dracula.csv

Title: Dracula
Author: Bram Stoker
python bin/countwords.py data/dracula.txt > results/dracula.csv

5) Create all results

The default target of our final Makefile re-creates results/collated.csv. Add a target to Makefile so that make results creates or updates any result files that are missing or out of date, but does not regenerate results/collated.csv.

6) The perils of shell wildcards

What is wrong with writing the rule for results/collated.csv like this:

results/collated.csv : results/*.csv
	python $(COLLATE) $^ > $@

(The fact that the result no longer depends on the program used to create it isn’t the biggest problem.)

7) Making documentation more readable

We can format the documentation in our Makefile more readably using this command:

## help : show all commands.
help :
	@grep -h -E '^##' ${MAKEFILE_LIST} | sed -e 's/## //g' \
	| column -t -s ':'

Using man and online search, explain what every part of this recipe does.

8) Configuration

A next step in automating this analysis might include moving the definitions of the COUNT, COLLATE, and PLOT variables into a separate file called config.mk:

COUNT=bin/countwords.py
COLLATE=bin/collate.py
PLOT=bin/plotcounts.py

and using the include command to access those definitions in the existing Makefile:

.PHONY: results all clean help settings

include config.mk

# ... the rest of the Makefile ...

Under what circumstances would this strategy be useful?