Make Concepts
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. Please note: you need to put a tab character at the beginning of every recipe line! This is an obscurity that catches the unwary. If you prefer to prefix your recipes with a character other than tab, you can set the .RECIPEPREFIX variable to an alternate character (see Other Special Variables).
Usually a recipe is in a rule with prerequisites and serves to create a target file if any of the prerequisites change. However, the rule that specifies a recipe for the target need not have prerequisites. For example, the rule containing the delete command associated with the target ‘clean’ does not have prerequisites.
A rule, then, explains how and when to remake certain files which are the targets of the particular rule. make carries out the recipe on the prerequisites to create or update the target. A rule can also explain how and when to carry out an action. See Writing Rules.
A makefile may contain other text besides rules, but a simple makefile need only contain rules. Rules may look somewhat more complicated than shown in this template, but all fit the pattern more or less.
.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.