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,
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.
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,
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 recipes 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.