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A Complete makefile example

Archive - Originally posted on "The Horse's Mouth" - 2012-03-14 06:56:15 - Graham Ellis

Part of a series, written to brush up some make notes I'm using for some make training next week

Let's write a complete makefile - from first principles:

  # This is our first makefile
  
  # Target "always" never exists, so rules will always run
  
  always:
      echo "Hello Make World"
  
  # Rule will only run if "once" already exists
  # By touching the file, we create it thus preventing re-runs
  
  once:
      echo "single shot"
      touch once
  
  # Target "clean" never exists, so this will always run
  # extra "@" supresses the echoing of the command being run
  # but you still see their output
  
  clean:
      @echo "Cleaning up"
      @rm once
      @echo "Completed"

Let's see that running:

  wizard:mc graham$ make -f firstmake
  echo "Hello Make World"
  Hello Make World
  wizard:mc graham$ make -f firstmake
  echo "Hello Make World"
  Hello Make World
  wizard:mc graham$ make -f firstmake once
  echo "single shot"
  single shot
  touch once
  wizard:mc graham$ make -f firstmake once
  make: `once' is up to date.
  wizard:mc graham$

Some things to note:

* If no dependencies are given, the rule is always applied (and if multiple dependencies are given, then the rules are applied if ANY of the files is newer than the target)

* touch is commonly used to create an empty file if you're wanting to perform actions and don't really need an output file at all.

* If you preceed a command with an @symbol, the command is not echoed out as it is run. The first two examples above rather nastily double up the echoed text, but in "clean" that's not the case.

* If an error occurs during the application of a rule, it will cease at that point:

  wizard:mc graham$ make clean
  Cleaning up
  rm: once: No such file or directory
  make: *** [clean] Error 1
  wizard:mc graham$

but an extra - sign will cause the error to be ignored in that the rule will continue:
    @-rm once

* The default makefile is called "makefile" or "Makefile" (both will work). You can use the -f command line option to specify a different file, or the MAKEFILES environment variable though this latter has some implications with regard to nesting of makefiles later on:

  wizard:mc graham$ export MAKEFILES=secondmake
  wizard:mc graham$ make clean
  Cleaning up
  wizard:mc graham$