Make

• GNU Make
  • Stuff for GNU Make
  • Managing Projects with GNU Make, 3.xth Edition
  • GNU Make Manual

variable assignment

• spaces before the variable value are ignored in variable assignments
• command line variable > makefile assigned variable > environment variable (> means override)

type	syntax	description
simply expanded variable	variable := value	righthand side is expanded immediately upon reading the line from the makefile
recursively expanded variable	vairable = value	the expansion is performed when the variable is used
conditional assignment variable	variable ?= value	this operator will perform the requested variable assignment only if the variable does not yet have a value
append assignment variable	variable += value	values on the righthand side of the assignment are appended to the variable without changing the original values in the variable

variable passing

source	description
MAKEFLAGS	Make automatically passes down variable values that were defined on the command line, by putting them in the MAKEFLAGS variable. When make starts, it automatically appends most command-line options to MAKEFLAGS except for —directory (-C), —file (-f), —old-file (-o), and —newfile (-W). The MAKEFLAGS variable is then exported to the environment and read by the sub-make as it starts.
MAKEOVERRIDES	The command line variable definitions really appear in the variable MAKEOVERRIDES, and MAKEFLAGS contains a reference to this variable.
export variable	to pass down, or export, a variable by explicit request, make adds the variable and its value to the environment for running each command
unexport variable	prevent a variable from being exported
environment	make exports a variable defined in the environment initially.
MAKEFILES	exported if you set it to anything. make considers its value as a list of names (separated by whitespace) of additional makefiles to be read before the others
MAKEFILE_LIST	$(word $(words $(MAKEFILE_LIST)), $(MAKEFILE_LIST)) returns the name of the most recently read makefile
SHELL	When make needs to pass a command line to a subshell, it uses /bin/sh. You can change the shell by setting the make variable SHELL.

variable expanding

• expanded immediately
  • lefthand side of the variable assignment
  • the righthand side of :=
  • the macro variable name for macro definitions
  • the targets and prerequisites for rules

• evaluation is deferred
  • the righthand side of = and ?=
  • the body of the macro for macro definitions
  • the commands for rules

syntax	description
$(var) or ${var}	expand the variable whose name is var
$(var:a=b) or ${var:a=b}	take the value of the variable var, replace every a at the end of a word with b in that value, and substitute the resulting string
$letter	a single character variable name does not require the parentheses
$@	representing the target
$*	target without its suffix
$%	the element of an archive member specification. For example, if the target is foo.a(bar.o) then ‘$%’ is bar.o and ‘$@’ is foo.a.
$<	the first prerequisite
$^	all the prerequisites, separated by spaces. This list has duplicate filenames removed. For prerequisites which are archive members, only the member named is used .
$+	all the prerequisites separated by spaces, including duplicates
$?	all prerequisites that are newer than the target, separated by spaces
$|	all the order-only prerequisites, with spaces between them

command prefix

prefix	description
'+' or contain the strings ‘$(MAKE)’ or ‘${MAKE}’	‘-n’, ‘-t’, and ‘-q’ options do not affect
'@' or make your target a prerequisite of the special target .SILENT if you want all of its commands to be hidden	do not echo the command
'-' or make the target a prerequisite of the .IGNORE special target	errors in the command should be ignored by make

function

syntax	description
$(eval text)	the argument to eval is expanded twice: once when when make prepares the argument list for eval, and once again by eval
$(value variable)	use the value of a variable without having it expanded
$(call macro-name[, param1…])	expands its first argument and replaces occurrences of $1, $2, etc., with the remaining arguments it is given

recursive

option	description
make —directory (-C)	cause make to change to the target directory before reading a makefile
make —print-directory (-w)	When make detects that it is invoking another make recursively, it enables the —print-directory (-w) option, which causes make to print the Entering directory and Leaving directory messages.
make —touch	The dependency graph is traversed and the selected targets and those prerequisites that are not marked .PHONY are brought up to date by executing touch on the target. Make automatically labels any line containing MAKE with the + modifier, meaning make runs the sub-make regardless of the —touch option.

convention variables

variable	default value	description
prefix	/usr/local	The root for the installation and two, and nothing should be directly installed into the directory.
exec_prefix	$(prefix)	The root for the installation that contains machine-specific files (such as executables and subroutine, and nothing should be directly installed into the directory.
bindir	$(exec_prefix)/bin or /usr/local/bin	executable programs that users can run
sbindir	$(exec_prefix)/sbin or /usr/local/sbin	executable programs that can be run from the shell, but are only generally useful to system administrators
libexecdir	$(exec_prefix)/libexecdir or /usr/local/libexecdir	executable programs to be run by other programs rather than by users. possibile subdirectories: $(libexecdir)/package-name/machine/version
datarootdir	$(prefix)/share or /usr/local/share	the root of the directory tree for read-only architecture-independent data
datadir	$(datarootdir) or /usr/local/share	idiosyncratic read-only architecture-independent data files for this program
sysconfdir	$(prefix)/etc or /usr/local/etc	read-only data files that pertain to a single machine
sharedstatedir	$(prefix)/com or /usr/local/com	architecture-independent data files which the programs modify while they run
localstatedir	$(prefix)/var or /usr/local/var	data files which the programs modify while they run, and that pertain to one specific machine
includedir	$(prefix)/include or /usr/local/include	header files to be included by user programs with the C ‘#include’ preprocessor directive
oldincludedir	/usr/include	include’ header files for use with compilers other than GCC
docdir	$(datarootdir)/doc/yourpkg or /usr/local/share/doc/yourpkg	documentation files (other than Info) for this package
infodir	$(datarootdir)/info or /usr/local/share/info	the Info files for this package
htmldir, dvidir, pdfdir, psdir	$(docdir)	documentation files in the particular format
libdir	$(exec_prefix)/lib or /usr/local/lib	object files and libraries of object code
mandir	$(datarootdir)/man	the top-level directory for installing the man pages (if any) for this package
srcdir		the directory for the sources being compiled