Make Manual

Cited from 2.2 A Simple Makefile

When a target is a file, it needs to be recompiled or relinked if any of its prerequisites change.

Targets that do not refer to files but are just actions are called phony targets.
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Cited from 2.3 How make Processes a Makefile

By default, make starts with the first target. This is called the default goal.

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Cited from 2.6 Another Style of Makefile

When the objects of a makefile are created only by implicit rules, an alternative style of makefile is possible. In this style of makefile, you group entries by their prerequisites instead of by their targets.
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Cited from 3.1 What Makefiles Contain

Makefiles contain five kinds of things: explicit rules, implicit rules, variable definitions, directives, and comments.

An implicit rule says when and how to remake a class of files based on their names. It describes how a target may depend on a file with a name similar to the target and gives a recipe to create or update such a target.

A directive is an instruction for make to do something special while reading the makefile. These include:

• Reading another makefile
• Deciding (based on the values of variables) whether to use or ignore a part of the makefile (see Conditional Parts of Makefiles).
• Defining a variable from a verbatim string containing multiple lines (see Defining Multi-Line Variables).

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Cited from 3.1.1 Splitting Long Lines

The way in which backslash/newline combinations are handled depends on whether the statement is a recipe line or a non-recipe line. Handling of backslash/newline in a recipe line is discussed later (see Splitting Recipe Lines).

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Cited from 3.2 What Name to Give Your Makefile

By default, when make looks for the makefile, it tries the following names, in order: GNUmakefile, makefile and Makefile.

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Cited from 3.3 Including Other Makefiles

The include directive tells make to suspend reading the current makefile and read one or more other makefiles before continuing. The directive is a line in the makefile that looks like this:

include filenames…

filenames can contain shell file name patterns. If filenames is empty, nothing is included and no error is printed. If the file names contain any variable or function references, they are expanded.

If the specified name does not start with a slash, and the file is not found in the current directory, several other directories are searched. First, any directories you have specified with the ‘-I’ or ‘--include-dir’ option are searched (see Summary of Options). Then the following directories (if they exist) are searched, in this order: prefix/include (normally /usr/local/include)/usr/gnu/include, /usr/local/include, /usr/include.

If you want make to simply ignore a makefile which does not exist or cannot be remade, with no error
message, use the -include directive instead of include, like this:

-include filenames…

For compatibility with some other make implementations, sinclude is another name for -include.

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Cited from 3.7 How make Reads a Makefile

Conditional directives are parsed immediately. This means, for example, that automatic variables cannot be used in conditional directives, as automatic variables are not set until the recipe for that rule is invoked. If you need to use automatic variables in a conditional directive you must move the condition into the recipe and use shell conditional syntax instead.

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Cited from 3.8 Secondary Expansion

If that special target is defined then in between the two phases mentioned above, right at the end of the read-in phase, all the prerequisites of the targets defined after the special target .SECONDEXPANSION are expanded a second time.