Make Concepts: Difference between revisions
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A target can be either the name of a file that is generated by the recipe, or the name of an action to carry out. These are phony named phony targets, because they are not files. | A target can be either the name of a file that is generated by the recipe, or the name of an action to carry out. These are phony named [[#.PHONY|phony targets]], because they are not files. | ||
A prerequisite is a file that is used as input to create the target. A target often depends on several files. | A prerequisite is a file that is used as input to create the target. A target often depends on several files. | ||
A recipe is an action that make carries out. A recipe may have more than one command, either on the same line or each on its own line. | A recipe is an action that "make" carries out. A recipe may have more than one command, either on the same line or each on its own line. You need to put a tab character at the beginning of every recipe line. <font color=darkkhaki>Is this still true?</font> Usually the recipe (re-)creates the target file if any of the prerequisites change. However, the rule that specifies a recipe for the target need not have prerequisites. | ||
=<tt>.PHONY</tt>= | =<tt>.PHONY</tt>= | ||
Revision as of 22:15, 10 January 2024
Internal
Rule
A makefile consists of rules with the following syntax:
target ...: prerequisites
recipe
A target can be either the name of a file that is generated by the recipe, or the name of an action to carry out. These are phony named phony targets, because they are not files.
A prerequisite is a file that is used as input to create the target. A target often depends on several files.
A recipe is an action that "make" carries out. A recipe may have more than one command, either on the same line or each on its own line. You need to put a tab character at the beginning of every recipe line. Is this still true? Usually the recipe (re-)creates the target file if any of the prerequisites change. However, the rule that specifies a recipe for the target need not have prerequisites.
.PHONY
By default, make targets are assumed to be files on disk. They will be built from other files as result of executing make with that name as argument. However, sometimes you want make to run commands that do not represent physical files in the filesystem, and if there's a file with the same name in the filesystem, make will be confused and will pick up the file. To avoid this, you can disambiguate with .PHONY:
.PHONY: clean
clean:
rm -rf *.o
Variables
CURDIR
CURDIR refers to the directory make is run from:
something:
"$(CURDIR)/scripts/something.sh"
Automatic Variables
$@
The file name of the target of the rule. In a pattern rule that has multiple targets $@ is the name of whichever target caused the rule’s recipe to be run.