workshops/slides/makefiles/makefiles.md

title	author	theme	colortheme
Making Makefiles	Malin	Warsaw	orchid

Intro

The fundamental problem:

git submodule update --init soundscape
cargo build --release
install -pm755 target/release/tap /usr/local/bin/

But you can't type this for run.

---

First Solution

#!/bin/sh
git submodule update --init soundscape
cargo build --release
install -pm755 target/release/tap /usr/local/bin/

At this point, every test takes 10 minutes.

Second Solution

#!/bin/sh
[ -f soundscape/.git ] || git submodule update --init soundscape
[ -f target/release/tap ] || cargo build --release
[ -f target/release/tap ] || \
    install -pm755 target/release/tap /usr/local/bin/

---

Makefile Solutions

• input, process, output.
• automatic idempotence

INSTALL_DIR = /usr/local/bin

soundscape/.git:
    git submodule update --init soundscape

/usr/local/bin/tap: target/release/tap
	install -pm755 target/release/tap $(INSTALL_DIR)

target/release/tap: src soundscape/.git
	cargo build --release

---

The Three Sigils

Readable, but slow:

forts/big_fort.txt: forts/short.txt forts/long.txt
	cat forts/short.txt forts/long.txt > forts/big_fort.txt

forts/:
	mkdir forts

forts/short.txt: forts/
	fortune -s > forts/short.txt

forts/long.txt: forts/
	fortune -l > forts/long.txt

---

Make this	From That	From These
$@	$<	$^

forts/big_fort.txt: forts/short.txt forts/long.txt
		cat $^ > $@

forts/: README.md
	mkdir $@
forts/short.txt: forts/
	fortune -s > $@
forts/long.txt: forts/
	fortune -l > $@

---

Gotcha: Directories

forts/big_fort.txt: forts/short.txt forts/long.txt
		cat $^ > $@

forts/: README.md
	mkdir $@
forts/short.txt: forts/
	fortune -s > $@
forts/long.txt: forts/
	fortune -l > $@

README.md:
    echo "Find the fortunes in the fort dir" > $@

---

Variables

include /etc/os-release
DAY != date +%d
MESSAGE != fortune -s

motd_$(DAY):
	$(info Placing message:)
	echo "Welcome to $(NAME)" > $@
	echo $(MESSAGE) >> $@

Gotcha: Hanging Quotes

echo "Welcome to "Arch Linux""

---

Add New Variables

make -f vars -e MESSAGE="Red alert, all hands on deck!"

Gotcha: Quote, or Risk Escape

make -f vars -e MESSAGE="<h1> HTML Headers </h1>"

---

Gotcha: Variables from Shell

This works:

file:
    $(info Hello $(USER))

...but not this:

file:
    user=bob
    echo $user

Nor this:

numbers:
    for x in 1 2 3 4 5; do
        echo $x
    done > $@

Nor this:

numbers:
    for x in 1 2 3 4 5; do echo $x ; done > $@

---

Ugly Fixes are Ugly

This works, but don't.

file:
	for x in 1 2 ;\
			do echo $$x ;\
	done > $@

---

Phonies, and the Problems with Lies

Clean

.PHONY: clean
clean:
    git clean -fdX

Gotcha: Recompiling without Changes

CHECKER = command -v
.PHONY: check
check:
	$(CHECKER) fortune >/dev/null
	$(CHECKER) cowsay >/dev/null

file: check # Needs a '|'
	fortune | cowsay > $@

---

Non-Compiling Checks

• make -n
• Gotcha: shell output variables.

---

The Fourth Sigil: %

Create standardized rules with %.

CP = ln -f

output: pngs/ldap.png

jpgs/ldap.jpg: ../../ldap/ldap.jpg
	mkdir -p $(dir $@)
	$(CP) $< $@

pngs/%.png: jpgs/%.jpg
	mkdir -p $(dir $@)
	$(info making $(@F) in $(@D))
	magick $< $@

---

Bling: makefile2graph

┌────────────────┐     ┌────────────────────┐
│ forts/long.txt │ ◀── │       forts/       │
└────────────────┘     └────────────────────┘
  │                      │
  │                      │
  │                      ▼
  │                    ┌────────────────────┐
  │                    │  forts/short.txt   │
  │                    └────────────────────┘
  │                      │
  │                      │
  │                      ▼
  │                    ┌────────────────────┐
  └──────────────────▶ │ forts/big_fort.txt │
                       └────────────────────┘

Gotcha: The Binary is Called make2graph

• Works with GUI tools maybe, IDK, I don't use Windows.
• Some systems can use graph-easy, but it's outdated.

---

Patsubst and Wildcards

IMAGES = $(wildcard jpgs/*)
COL = $(patsubst jpgs/%,collection/%,$(IMAGES))

.PHONY: show
show:
	$(info IMAGES is $(IMAGES))
	$(info Col is $(COL))

.PHONY: output
output: $(COL)

collection/%.jpg: jpgs/%.jpg
	mkdir -p $(@D)
	cp $< $@

---

Use Cases

• Backups
• Making Websites