Makefile Variables & Pattern Rules

Intermediatev1.0.0

Master Makefile variables, pattern rules, and functions — environment overrides, conditional logic, automatic variables, and DRY patterns for maintainable build files.

Content

Overview

Makefile variables and pattern rules eliminate duplication and make build files maintainable. Variables define reusable values, pattern rules handle repetitive targets, and functions transform strings — all essential for Makefiles beyond trivial use.

Why This Matters

-DRY builds — define once, use everywhere
-Environment overrides — make deploy ENV=staging
-Pattern rules — one rule handles many files
-Maintainability — change a version/path in one place

Variable Types

Simple vs Recursive

makefile

# Immediate (simple) — evaluated once at definition
VERSION := $(shell git describe --tags --always)
BUILD_TIME := $(shell date -u +%Y-%m-%dT%H:%M:%SZ)

# Recursive — evaluated each time used
GOFLAGS = -ldflags "-X main.version=$(VERSION)"

# Overridable default — user can override from CLI
ENV ?= development
PORT ?= 8080

# Conditional
ifdef CI
  GOFLAGS += -v
endif

Using Variables

makefile

APP_NAME := myapp
VERSION := $(shell git describe --tags --always)
DOCKER_IMAGE := $(APP_NAME):$(VERSION)
GO_FILES := $(shell find . -name '*.go' -not -path './vendor/*')

.PHONY: build
build: ## Build the application
	go build $(GOFLAGS) -o bin/$(APP_NAME) ./cmd/$(APP_NAME)

.PHONY: docker-build
docker-build: ## Build Docker image
	docker build -t $(DOCKER_IMAGE) .

# Override from command line:
# make build GOFLAGS="-race"
# make deploy ENV=production

Pattern Rules

makefile

# Compile all .proto files to .go
%.pb.go: %.proto
	protoc --go_out=. $<

# Build all cmd/ binaries
bin/%: cmd/%/main.go
	go build -o $@ ./$(<D)

# Generate all .css from .scss
dist/%.css: src/%.scss
	sass $< $@

Automatic Variables

Variable	Meaning	Example
`$@`	Target name	bin/myapp
`$<`	First prerequisite	cmd/myapp/main.go
`$^`	All prerequisites	file1.go file2.go
`$*`	Pattern stem	myapp (from bin/%)
`$(@D)`	Directory of target	bin/
`$(<D)`	Directory of first prereq	cmd/myapp/

Functions

makefile

# Find files
SOURCES := $(wildcard src/*.go)
TESTS := $(wildcard *_test.go)

# String manipulation
OBJECTS := $(SOURCES:.go=.o)
BINARIES := $(addprefix bin/,app1 app2 app3)

# Shell execution
GIT_HASH := $(shell git rev-parse --short HEAD)

Best Practices

-Use := for most variables — predictable evaluation
-Use ?= for overridable defaults — CLI-friendly
-Use pattern rules for repetitive file transformations
-Group variables at the top of the Makefile
-Use $(shell ...) sparingly — each call spawns a subshell

Common Mistakes

-Using = when := is intended (unexpected lazy evaluation)
-Not quoting shell commands inside $(shell ...)
-Forgetting that each recipe line runs in a separate shell
-Using pattern rules for targets that aren't file-based

FAQ

Discussion

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Variable Types

Simple vs Recursive

makefile

# Immediate (simple) — evaluated once at definition
VERSION := $(shell git describe --tags --always)
BUILD_TIME := $(shell date -u +%Y-%m-%dT%H:%M:%SZ)

# Recursive — evaluated each time used
GOFLAGS = -ldflags "-X main.version=$(VERSION)"

# Overridable default — user can override from CLI
ENV ?= development
PORT ?= 8080

# Conditional
ifdef CI
  GOFLAGS += -v
endif

Using Variables

makefile

APP_NAME := myapp
VERSION := $(shell git describe --tags --always)
DOCKER_IMAGE := $(APP_NAME):$(VERSION)
GO_FILES := $(shell find . -name '*.go' -not -path './vendor/*')

.PHONY: build
build: ## Build the application
	go build $(GOFLAGS) -o bin/$(APP_NAME) ./cmd/$(APP_NAME)

.PHONY: docker-build
docker-build: ## Build Docker image
	docker build -t $(DOCKER_IMAGE) .

# Override from command line:
# make build GOFLAGS="-race"
# make deploy ENV=production

# Compile all .proto files to .go %.pb.go: %.proto protoc --go_out=. $< # Build all cmd/ binaries bin/%: cmd/%/main.go go build -o $@ ./$(<D) # Generate all .css from .scss dist/%.css: src/%.scss sass $< $@

Variable

Meaning

Example

`$@`

Target name

bin/myapp

`$<`

First prerequisite

cmd/myapp/main.go

`$^`

All prerequisites

file1.go file2.go

`$*`

Pattern stem

myapp (from bin/%)

`$(@D)`

Directory of target

bin/

`$(<D)`

Directory of first prereq

cmd/myapp/

# Find files SOURCES := $(wildcard src/*.go) TESTS := $(wildcard *_test.go) # String manipulation OBJECTS := $(SOURCES:.go=.o) BINARIES := $(addprefix bin/,app1 app2 app3) # Shell execution GIT_HASH := $(shell git rev-parse --short HEAD)