Make utility

In POSIX systems make is a utility to manage pojects—programs, libraries, articles, reports, web-sites, and others—where files must be manipulated according to certain rules.

When make is run, it reads the description of the project from a makefile and then automatically updates the project, if necessary, according to the rules in the makefile.

Makefile

Makefile contains a description of the project in the declarative makefile language. By default a makefile must have the name Makefile or makefile. If the makefile is called SomethingElse then the make utility must be called as make -f SomethingElse.

A makefile consists of macro definitions and rules. It resembles a cookbook.

Macro definitions

A macro definition looks like a normal assignment in a programming language, for example

CSFLAGS = -optimize+ -platform:arm

The macro can then be called as $(CSFLAGS) and will return the string -optimize+ -platform:arm.

Rules

A rule looks very much like an instruction for preparing a dish. It has the following syntax,

dish : ingredients
⊣recipe

where the sign ⊣ denotes the (mostly invisible, unfortunately) tabulator-sign. Yes, by default a recipie starts with the tabulator-sign. This aspect has been a subject of critisism, so in the GNU-make version 3.82+ one can change the default tabulator-sign to any other sign—for example a semicolon ;—by defining a macro .RECIPEPREFIX := ;.

The rule is interpreted like the following:

Our goal is to make 'dish'.
Before making the dish, all 'ingredients' must be made (usually according to their own 'recipies').
Once all 'ingrediens' are made, the 'dish' is made according to the 'recipie'.

The GNU-make manual uses a somewhat different notation,

target : prerequisites
⊣recipe

If the recipie consists of one command only, it can be writte in the same line as the target,

target : prerequisites ; recipe

By default 'make' only builds the first target it finds in the makefile. Therefore if more than one targets must be built one makes a "phoney" target that depends on the targets that must be built by default,

.PHONEY: default
default : target1 target2 target3

'Hello world' example

Suppose we have a project to create a file out.txt with the text "hello world" using a 'hello world' C#-program wholly contained in the file "hello.cs".

The makefile for the project could look like this,

out.txt : hello.exe         # out.txt depends on bytecode executable hello.exe
⊣mono hello.exe > out.txt  # run hello.exe in mono, redirect output into out.txt

hello.exe : hello.cs           # bytecode hello.exe depends on source-code hello.cs
⊣mcs -out:hello.exe hello.cs   # compile hello.cs, output goes to hello.exe

.PHONEY:clean           # clean is a phoney target
clean:                  # does not depend on anything
⊣rm --force out.txt hello.exe # remove the files produced by making

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