workshops/slides/makefiles/makefiles.md

---
title:
- Making Makefiles
author:
- Malin

theme:
- Warsaw
colortheme:
- orchid
---

# Intro

The fundamental problem:

```bash
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

```bash
#!/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

```bash
#!/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

```bash
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:

```make fort_1
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 |
|:---------:|:---------:|:----------:|
|  `$@`     |  `$<`     |   `$^`     |


```make fort_2
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


```make fort_2
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

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

### Gotcha: Quote, or Risk Escape

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

***

# Gotcha: Variables from Shell

This works:

```make
file:
    $(info Hello $(USER))
```

...but not this:

```make
file:
    user=bob
    echo $user
```

Nor this:

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

Nor this:

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

***

### Ugly Fixes are Ugly

This works, but don't.

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

***


# Phonies, and the Problems with Lies

## Clean


```make
.PHONY: clean
clean:
    git clean -fdX
```

## Gotcha: Recompiling without Changes

```make
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 `%`.


```make rules
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

```graph

┌────────────────┐     ┌────────────────────┐
│ 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


```make pats
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