16  Make - Cheatsheet

Make runs a command when its output is missing or older than one of its inputs. It is useful when a data pipeline has several steps that must run in the right order. The Pipelines, Automation, and CI/CD chapter explains why this matters; use this page when you need to write or run a small makefile.

16.1 Anatomy of a Rule

target: prerequisite1 prerequisite2
    command-that-builds-target

The target is the file you want to create, the prerequisites are the files it depends on, and the indented recipe is the command that creates it. The recipe line begins with a tab, not spaces (unless you deliberately configure Make otherwise). Make compares file modification times; it does not inspect whether an R script’s contents are semantically different.

For example, put the following in a file named Makefile in a small standalone project. Assume report.qmd and data/clean.csv already exist:

all: report.html

report.html: report.qmd data/clean.csv
    quarto render report.qmd

.PHONY: all clean
clean:
    rm -f report.html

The first target, all, is the default. If the report does not exist, or report.qmd or data/clean.csv is newer, Make runs Quarto to regenerate report.html. Including both inputs matters: if you omit data/clean.csv, Make has no reason to rebuild the report when that data file changes. .PHONY tells Make that all and clean are command names rather than output files.

This example assumes rendering report.qmd produces report.html in the working directory. Check the actual output path if your Quarto project uses an output directory. In a full pipeline, you would add a rule to build data/clean.csv from a raw dataset and an R script, keeping the raw file untouched.

16.2 Commands at a Glance

Goal	Command
Build the default target	make
Build only a named target	make report.html
Preview commands without running them	make -n
Rebuild regardless of timestamps	make -B
Run the clean recipe above	make clean

make -n is useful before an expensive rebuild. The clean recipe above deletes only the generated HTML report, not the input data or source file; inspect a project’s own clean or wipe rule before running it. To test reproducibility, clean generated outputs and rebuild them from the raw inputs and code—after confirming the pipeline contains every dependency.

TipWhen Make Seems to Do Nothing

If Make says the target is up to date when it should change, check that the rule names the actual output file and lists every input, including scripts and templates. If a recipe runs but no target appears, Make will run it again next time; make sure the command produces the file named on the left of the colon.