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Make utility

In POSIX systems "make" is a utility to manage pojects on a computer (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 (normally called "Makefile" or "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 resembles a cookbook and consists of macro definitions and rules.

Macro definitions

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

MCS = mcs -optimize+ -platform:arm

The macro can then be called as $(MCS) and will return the string "mcs -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', "make" will automatically look through the makefile to find and execute the recipes for all ingredients).
Once all 'ingrediens' are made, the 'dish' is made according to its 'recipie'.

The GNU-make manual uses a somewhat different notation,

target : prerequisites
	recipe

If the recipie consists of one command only, it can be written 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 target 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

If one wishes, one can build not the first but any target in the makefile, say 'test', with the command

make test

Hint: bash-completion feature actually works on the targets in the current Makefile.

'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 (comments in the makefile start with the hash-sign #),

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, put the executable bytecode into hello.exe

.PHONEY:clean                         # clean is a phoney target, not a file
clean:                                # does not depend on anything
	rm --force Out.txt hello.exe  # remove the files produced in the process of making