Next: Makefile Names Up: Makefiles
What Makefiles Contain
Makefiles contain five kinds of things: "explicit rules", "implicit
rules", "variable definitions", "directives", and "comments". Rules,
variables, and directives are described at length in later chapters.
* An "explicit rule" says when and how to remake one or more files,
called the rule's targets. It lists the other files that the
targets "depend on", and may also give commands to use to create
or update the targets. Note: Writing Rules.
* 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 commands to
create or update such a target. *Note Using Implicit Rules:
* A "variable definition" is a line that specifies a text string
value for a variable that can be substituted into the text later.
The simple makefile example shows a variable definition for
`objects' as a list of all object files (Note: Variables Make
* A "directive" is a command for `make' to do something special while
reading the makefile. These include:
* Reading another makefile (*note Including Other Makefiles:
* Deciding (based on the values of variables) whether to use or
ignore a part of the makefile (Note: Conditional Parts of
* Defining a variable from a verbatim string containing
multiple lines (Note: Defining Variables Verbatim.).
* `#' in a line of a makefile starts a "comment". It and the rest of
the line are ignored, except that a trailing backslash not escaped
by another backslash will continue the comment across multiple
lines. Comments may appear on any of the lines in the makefile,
except within a `define' directive, and perhaps within commands
(where the shell decides what is a comment). A line containing
just a comment (with perhaps spaces before it) is effectively
blank, and is ignored.
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