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