makefile.md

   1 ---
   2 title: Makefile
   3 prism_languages: [makefile]
   4 layout: 2017/sheet
   5 category: CLI
   6 ---
   7
   8 ## Var assignment
   9
  10 ```makefile
  11 foo  = "bar"
  12 bar  = $(foo) foo  # dynamic (renewing) assignment
  13 foo := "boo"       # one time assignment, $(bar) now is "boo foo"
  14 foo ?= /usr/local  # safe assignment, $(foo) and $(bar) still the same
  15 bar += world       # append, "boo foo world"
  16 foo != echo fooo   # exec shell command and assign to foo
  17 # $(bar) now is "fooo foo world"
  18 ```
  19
  20 `=` expressions are only evaluated when they're being used.
  21
  22 ## Magic variables
  23
  24 ```makefile
  25 out.o: src.c src.h
  26   $@   # "out.o" (target)
  27   $<   # "src.c" (first prerequisite)
  28   $^   # "src.c src.h" (all prerequisites)
  29
  30 %.o: %.c
  31   $*   # the 'stem' with which an implicit rule matches ("foo" in "foo.c")
  32
  33 also:
  34   $+   # prerequisites (all, with duplication)
  35   $?   # prerequisites (new ones)
  36   $|   # prerequisites (order-only?)
  37
  38   $(@D) # target directory
  39 ```
  40
  41 ## Command prefixes
  42
  43 | Prefix | Description                                 |
  44 | ------ | ------------------------------------------- |
  45 | `-`    | Ignore errors                               |
  46 | `@`    | Don't print command                         |
  47 | `+`    | Run even if Make is in 'don't execute' mode |
  48
  49 ```makefile
  50 build:
  51     @echo "compiling"
  52     -gcc $< $@
  53
  54 -include .depend
  55 ```
  56
  57 ## Find files
  58
  59 ```makefile
  60 js_files  := $(wildcard test/*.js)
  61 all_files := $(shell find images -name "*")
  62 ```
  63
  64 ## Substitutions
  65
  66 ```makefile
  67 file     = $(SOURCE:.cpp=.o)   # foo.cpp => foo.o
  68 outputs  = $(files:src/%.coffee=lib/%.js)
  69
  70 outputs  = $(patsubst %.c, %.o, $(wildcard *.c))
  71 assets   = $(patsubst images/%, assets/%, $(wildcard images/*))
  72 ```
  73
  74 ## More functions
  75
  76 ```makefile
  77 $(strip $(string_var))
  78
  79 $(filter %.less, $(files))
  80 $(filter-out %.less, $(files))
  81 ```
  82
  83 ## Building files
  84
  85 ```makefile
  86 %.o: %.c
  87   ffmpeg -i $< > $@   # Input and output
  88   foo $^
  89 ```
  90
  91 ## Includes
  92
  93 ```makefile
  94 -include foo.make
  95 ```
  96
  97 ## Options
  98
  99 ```sh
 100 make
 101   -e, --environment-overrides
 102   -B, --always-make
 103   -s, --silent
 104   -j, --jobs=N   # parallel processing
 105 ```
 106
 107 ## Conditionals
 108
 109 ```makefile
 110 foo: $(objects)
 111 ifeq ($(CC),gcc)
 112   $(CC) -o foo $(objects) $(libs_for_gcc)
 113 else
 114   $(CC) -o foo $(objects) $(normal_libs)
 115 endif
 116 ```
 117
 118 ## Recursive
 119
 120 ```makefile
 121 deploy:
 122   $(MAKE) deploy2
 123 ```
 124
 125 ## Further reading
 126
 127 - [isaacs's Makefile](https://gist.github.com/isaacs/62a2d1825d04437c6f08)
 128 - [Your Makefiles are wrong](https://tech.davis-hansson.com/p/make/)
 129 - [Manual](https://www.gnu.org/software/make/manual/html_node/index.html)