260 lines
5.2 KiB
Markdown
Executable File
260 lines
5.2 KiB
Markdown
Executable File
#!/bin/env slides
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# Makefiles Are Cool
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_By Bruce Hill_
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--------------------------
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# First Experiences with Makefiles Suck
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- Some college course gave you this thing that magically
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makes your code compile.
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- Some open source project has an autogenerate script that
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makes a 20,000 line makefile.
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- Configuration options are often poorly documented.
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- Just run `make` and pray it works.
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--------------------------
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# Actually Make Is Good
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- Really useful for small projects
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- Not just compiling C code
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- Anything where files are used to make other files
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--------------------------
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# What Even Is Make?
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`make` is a command you run to compile stuff.
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--------------------------
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# What Even Is Make?
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`make` is a bunch of similar programs (most commonly GNU)
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that look at files and determines which files need to be
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rebuilt and how.
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--------------------------
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# What Even Is Make?
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`make` is a domain specific programming language
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and interpreter for expressing dependency trees
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and production rule systems.
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--------------------------
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# What Even Is Make?
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`make` is a lightweight way to have files turn
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into other files lazily using simple rules.
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--------------------------
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# Makefiles
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When you run `make`, it looks for a file called
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`Makefile` or `makefile` with a set of rules.
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Each rule has the format:
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```make
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output: input1 input2 input3...
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how to build...
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```
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The body of the rule is a _shell script_
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**The rule will only run if any of the input files has
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been modified more recently than the output file!**
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----------------------------
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# Simple Example
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```make
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sorted_names.txt: names.txt
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sort names.txt > sorted_names.txt
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```
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If you ever modify `names.txt`, you can run
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`make sorted_names.txt` to create the sorted names file.
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If you don't want to retype the filename, you can use
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the variables `$<` (input files), `$@` (output file),
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and `$^` (first input file):
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```make
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sorted_names.txt: names.txt
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sort $< > $@
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```
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-----------------------------
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# Another Example
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Run a python script to draw an image:
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```make
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graph.png: plot_graph.py graph_module.py
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python3 $^
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```
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This will re-run if either `plot_graph.py` or
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`graph_module.py` is edited.
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----------------------------
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# Dependency Trees
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Rules can form dependency trees:
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```make
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graph.png: plot_graph.py data.csv
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python3 plot_graph.py data.csv
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data.csv: raw_data.bin
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convert_bin_to_csv raw_data.bin
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```
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Running `make graph.png` will first make sure that
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`plot_graph.py` and `data.csv` are up-to-date,
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then make sure that `graph.png` is up-to-date.
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Rules are **lazy**, so if you edit `plot_graph.py`, but
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don't touch `raw_data.bin`, then running `make graph.png`
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won't run `convert_bin_to_csv` because it's not necessary.
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----------------------------
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# Phony Rules
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Sometimes you have a rule that doesn't actually have
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a file ouput.
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You can use `.PHONY` to tell `make` to not bother looking
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for a file with that name.
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Most commonly used for `all`, `clean`, and `install`:
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```make
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.PHONY all clean install
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all: sorted_names.txt graph.png
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clean:
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rm sorted_names.txt graph.png
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install: sorted_names.txt graph.png
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cp $< /etc/cool-files/
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```
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**Note 1:** a rule with no body just means "I need these
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files to be built using their rules, but I don't do anything
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in particular"
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**Note 2:** when you run just `make` with no arguments, it
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runs the _first_ rule in the file, which is usually `all`
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----------------------------
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# Pattern Rules
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If you put a `%` in the name, you can do reusable pattern
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rules that work for different filenames.
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## Turn Markdown Files into PDFs
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```make
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%.pdf: %.md
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pandoc $< -o $@
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```
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## Compile C Code
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```make
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%.o: %.c %.h
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cc -c $^ -o $@
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```
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-----------------------------
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# Defining Variables
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You can define variables that are reused in different
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rules like this:
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```make
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O=-O2
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CFLAGS=-Wall -Werror $O
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all: program
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program: main.c foo.o baz.o
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cc $CFLAGS $< -o $@
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%.o: %.c %.h
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cc $CFLAGS -c $^ -o $@
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```
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When running `make` you can override these variables if you
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want to:
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```bash
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make O=-O1 CFLAGS='-Weverything -Werror' all
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```
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**Warning:** changing the variables does not change file
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modification times, so `make` won't know stuff needs to
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be rebuilt with different flags.
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--------------------------------
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# My Website
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I use a makefile to build my website and blog:
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- `pandoc` to make HTML files from markdown files.
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- A janky bash script to make an RSS feed from my blogposts.
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- `gzip` to compress my CSS files.
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- `rsync` PHONY rule to send files to my server.
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--------------------------------
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# Not Covered
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There's a bunch of stuff not covered in the talk:
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- Platform-dependent variables
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- Pattern matching variables (get all the files of a type)
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- Built-in rules (you can run `make` even without a makefile)
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- Silent commands with `@`
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- [Read the docs](https://www.gnu.org/software/make/manual/html_node/index.html)
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- You can use pandoc to make a website
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- You can use pandoc to make manpages for programs
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- You can use pandoc for anything
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- Please don't make scripts to autogenerate 10K+ line makefiles
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-------------------------------
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# The End
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Thanks! Hope you try using simple
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Makefiles for your own projects!
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