GNU `make'

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## Using Implicit Rules

Certain standard ways of remaking target files are used very often. For example, one customary way to make an object file is from a C source file using the C compiler, `cc`.

Implicit rules tell `make` how to use customary techniques so that you do not have to specify them in detail when you want to use them. For example, there is an implicit rule for C compilation. File names determine which implicit rules are run. For example, C compilation typically takes a `.c` file and makes a `.o` file. So `make` applies the implicit rule for C compilation when it sees this combination of file name endings.

A chain of implicit rules can apply in sequence; for example, `make` will remake a `.o` file from a `.y` file by way of a `.c` file.

The built-in implicit rules use several variables in their commands so that, by changing the values of the variables, you can change the way the implicit rule works. For example, the variable `CFLAGS` controls the flags given to the C compiler by the implicit rule for C compilation.

You can define your own implicit rules by writing pattern rules.

Suffix rules are a more limited way to define implicit rules. Pattern rules are more general and clearer, but suffix rules are retained for compatibility.