Each rule has a target, a file to be created, or built.
Each rule has zero or more dependencies, files that are needed to
build the target.
: separates the target and the dependencies.
Dependencies are separated by spaces.
Each rule has zero or more actions, commands to run to build the
target using the dependencies.
Actions are indented using the TAB character, not 8 spaces.
Dependencies:
If any dependency does not exist then Make will look for a rule to
build it.
The order of rebuilding dependencies is arbitrary. You should not
assume that they will be built in the order in which they are listed.
Dependencies must form a directed acyclic graph. A target cannot
depend on a dependency which, in turn depends upon, or has a
dependency which depends upon, that target.
If a list of dependencies or an action is too long, a Makefile can
become more difficult to read.
Backslash,\, the line continuation character, allows you to split
up a list of dependencies or an action over multiple lines, to make
them easier to read.
Make will combine the multiple lines into a single list of dependencies
or action.
Phony targets:
.PHONY : clean
clean :
rm -f *.dat
Phony targets are a short-hand for sequences of actions.
No file with the target name is built when a rule with a phony
target is run.
Automatic variables:
$< denotes ‘the first dependency of the current rule’.
$@ denotes ‘the target of the current rule’.
$^ denotes ‘the dependencies of the current rule’.
$* denotes ‘the stem with which the pattern of the current rule matched’.
The steps a build manager must take to create or
update a file or other object.
assignment
A request that Make stores something in a
variable.
automatic variable
A variable whose value is automatically redefined for each
rule. Make’s automatic variables include $@,
which holds the rule’s target, $^, which holds its
dependencies, and, $<, which holds the first of
its dependencies, and $*, which holds the stem with which
the pattern was matched. Automatic variables are typically used in
pattern rules.
A file that a target depends on. If any of a target’s
dependencies are newer than the target itself, the
target needs to be updated. A target’s dependencies are also
called its prerequisites. If a target’s dependencies do not exist,
then they need to be built first.
false dependency
This can refer to a dependency that is artificial.
e.g. a false dependency is introduced if a data analysis script
is added as a dependency to the data files that the script
analyses.
function
A built-in Make utility that performs some operation, for
example gets a list of files matching a pattern.
incremental build
The feature of a build manager by
which it only rebuilds files that, either directory
or indirectly, depend on a file that was changed.
macro
Used as a synonym for variable in certain versions of
Make.
A build file used by Make, which, by
default, are named Makefile.
pattern rule
A rule that specifies a general way to build or update an
entire class of files that can be managed the same way. For
example, a pattern rule can specify how to compile any C file
rather than a single, specific C file, or, to analyze any data
file rather than a single, specific data file. Pattern rules
typically make use of automatic variables
and wildcards.
phony target
A target that does not correspond to a file or other
object. Phony targets are usually symbolic names for sequences of
actions.
A request that Make substitutes the name of a
variable for its value.
rule
A specification of a target’s
dependencies and what actions need to be
executed to build or update the target.
stem
The part of the target that was matched by the pattern rule. If
the target is file.dat and the target pattern was %.dat, then
the stem $* is file.
target
A thing to be created or updated, for example a file. Targets can
have dependencies that must exist, and be
up-to-date, before the target itself can be built or updated.
A pattern that can be specified in dependencies and
targets. If Make finds a dependency matching
the pattern, then the pattern is substituted into the
target. wildcards are often used in pattern
rules. The Make wildcard is %.