make: Special Variables
6.14 Other Special Variables
============================
GNU 'make' supports some variables that have special properties.
'MAKEFILE_LIST'
Contains the name of each makefile that is parsed by 'make', in the
order in which it was parsed. The name is appended just before
'make' begins to parse the makefile. Thus, if the first thing a
makefile does is examine the last word in this variable, it will be
the name of the current makefile. Once the current makefile has
used 'include', however, the last word will be the just-included
makefile.
If a makefile named 'Makefile' has this content:
name1 := $(lastword $(MAKEFILE_LIST))
include inc.mk
name2 := $(lastword $(MAKEFILE_LIST))
all:
@echo name1 = $(name1)
@echo name2 = $(name2)
then you would expect to see this output:
name1 = Makefile
name2 = inc.mk
'.DEFAULT_GOAL'
Sets the default goal to be used if no targets were specified on
the command line (
Arguments to Specify the Goals Goals.).
The '.DEFAULT_GOAL' variable allows you to discover the current
default goal, restart the default goal selection algorithm by
clearing its value, or to explicitly set the default goal. The
following example illustrates these cases:
# Query the default goal.
ifeq ($(.DEFAULT_GOAL),)
$(warning no default goal is set)
endif
.PHONY: foo
foo: ; @echo $@
$(warning default goal is $(.DEFAULT_GOAL))
# Reset the default goal.
.DEFAULT_GOAL :=
.PHONY: bar
bar: ; @echo $@
$(warning default goal is $(.DEFAULT_GOAL))
# Set our own.
.DEFAULT_GOAL := foo
This makefile prints:
no default goal is set
default goal is foo
default goal is bar
foo
Note that assigning more than one target name to '.DEFAULT_GOAL' is
invalid and will result in an error.
'MAKE_RESTARTS'
This variable is set only if this instance of 'make' has restarted
(How Makefiles Are Remade Remaking Makefiles.): it will
contain the number of times this instance has restarted. Note this
is not the same as recursion (counted by the 'MAKELEVEL' variable).
You should not set, modify, or export this variable.
'MAKE_TERMOUT'
'MAKE_TERMERR'
When 'make' starts it will check whether stdout and stderr will
show their output on a terminal. If so, it will set 'MAKE_TERMOUT'
and 'MAKE_TERMERR', respectively, to the name of the terminal
device (or 'true' if this cannot be determined). If set these
variables will be marked for export. These variables will not be
changed by 'make' and they will not be modified if already set.
These values can be used (particularly in combination with output
synchronization (Output During Parallel Execution Parallel
Output.) to determine whether 'make' itself is writing to a
terminal; they can be tested to decide whether to force recipe
commands to generate colorized output for example.
If you invoke a sub-'make' and redirect its stdout or stderr it is
your responsibility to reset or unexport these variables as well,
if your makefiles rely on them.
'.RECIPEPREFIX'
The first character of the value of this variable is used as the
character make assumes is introducing a recipe line. If the
variable is empty (as it is by default) that character is the
standard tab character. For example, this is a valid makefile:
.RECIPEPREFIX = >
all:
> @echo Hello, world
The value of '.RECIPEPREFIX' can be changed multiple times; once
set it stays in effect for all rules parsed until it is modified.
'.VARIABLES'
Expands to a list of the _names_ of all global variables defined so
far. This includes variables which have empty values, as well as
built-in variables (Variables Used by Implicit Rules
Implicit Variables.), but does not include any variables which are
only defined in a target-specific context. Note that any value you
assign to this variable will be ignored; it will always return its
special value.
'.FEATURES'
Expands to a list of special features supported by this version of
'make'. Possible values include, but are not limited to:
'archives'
Supports 'ar' (archive) files using special file name syntax.
Using 'make' to Update Archive Files Archives.
'check-symlink'
Supports the '-L' ('--check-symlink-times') flag.
Summary of Options Options Summary.
'else-if'
Supports "else if" non-nested conditionals. Syntax of
Conditionals Conditional Syntax.
'jobserver'
Supports "job server" enhanced parallel builds.
Parallel Execution Parallel.
'oneshell'
Supports the '.ONESHELL' special target. Using One
Shell One Shell.
'order-only'
Supports order-only prerequisites. Types of
Prerequisites Prerequisite Types.
'second-expansion'
Supports secondary expansion of prerequisite lists.
'shortest-stem'
Uses the "shortest stem" method of choosing which pattern, of
multiple applicable options, will be used. How Patterns
Match Pattern Match.
'target-specific'
Supports target-specific and pattern-specific variable
assignments. Target-specific Variable Values
Target-specific.
'undefine'
Supports the 'undefine' directive. Undefine
Directive.
'guile'
Has GNU Guile available as an embedded extension language.
GNU Guile Integration Guile Integration.
'load'
Supports dynamically loadable objects for creating custom
extensions. Loading Dynamic Objects Loading Objects.
'.INCLUDE_DIRS'
Expands to a list of directories that 'make' searches for included
makefiles (Including Other Makefiles Include.).
Info Catalog
make: Suppressing Inheritance
make: Using Variables