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---
title: GNU Make
---
Best practices for my Makefiles (sorry for the botched highlighting).
```make
# Put this in the top of the Makefile:
MAKEFLAGS += --no-builtin-rules --no-builtin-variables --warn-undefined-variables
unexport MAKEFLAGS
.DEFAULT_GOAL := all
.DELETE_ON_ERROR:
.SUFFIXES:
SHELL := bash
.SHELLFLAGS := -eu -o pipefail -c
escape = $(subst ','\'',$(1))
define noexpand
ifeq ($$(origin $(1)),environment)
$(1) := $$(value $(1))
endif
ifeq ($$(origin $(1)),environment override)
$(1) := $$(value $(1))
endif
ifeq ($$(origin $(1)),command line)
override $(1) := $$(value $(1))
endif
endef
# OK, now some examples of how to use it:
.PHONY: all
all: test-escape test-noexpand
# Always put command arguments in single quotes.
# Escape variables and shell output using the escape function.
var_with_quote := Includes ' quote
.PHONY: test-escape
test-escape:
printf '%s\n' '$(call escape,$(var_with_quote))'
printf '%s\n' '$(call escape,$(shell echo "Includes ' quote"))'
# The above recipe will print "Includes ' quote" twice.
# If you define variables using ?= or use environment variables in your
# Makefile, use noexpand on them (to safeguard against ${accidental}
# references).
var_with_default ?= Accidental reference?
$(eval $(call noexpand,var_with_default))
$(eval $(call noexpand,env_var))
.PHONY: test-noexpand
test-noexpand:
printf '%s\n' '$(call escape,$(var_with_default))'
printf '%s\n' '$(call escape,$(env_var))'
# The above recipe will print "Accidental ${reference}" twice if you run using
# env_var='Accidental ${reference}' make var_with_default='Accidental ${reference}'
```
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