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gmake directives

define

Defines a variable.

endif

, anchor=>'endif')

export

Exports a variable so that it can be used in a recursivly invoked make. 
export var=val
export var:=val
export var+=val
In order to export all variables, export must be alone on a line: 
export

Example

A directory containing a Makefile and a sub directory (appropriatly called subdir): 
C:\temp\mk>dir
 Volume in drive C has no label.
 Volume Serial Number is EC22-DD8D

 Directory of C:\temp\mk

12/06/2004  11:55 AM    <DIR>          .
12/06/2004  11:55 AM    <DIR>          ..
12/06/2004  11:55 AM               191 Makefile
12/06/2004  11:55 AM    <DIR>          subdir
               1 File(s)            191 bytes
The makefile in the upper directory:
Makefile
export VAR_EXPORTED=I am exported
VAR_LOCAL=I am not exported

all: subdir

subdir:
	@echo VAR_EXPORTED: $(VAR_EXPORTED) VAR_LOCAL: $(VAR_LOCAL)
	@$(MAKE) -C subdir
	@echo VAR_EXPORTED: $(VAR_EXPORTED) VAR_LOCAL: $(VAR_LOCAL)

.PHONY: subdir
The makefile in the subdir directory:
subdir\Makefile
VAR_EXPORTED+=locally appended
all:
	@echo VAR_EXPORTED: $(VAR_EXPORTED) VAR_LOCAL: $(VAR_LOCAL)
Invoking make prints: 
VAR_EXPORTED: I am exported VAR_LOCAL: I am not exported
mingw32-make[1]: Entering directory `C:/temp/mk/subdir'
VAR_EXPORTED: I am exported locally appended VAR_LOCAL:
mingw32-make[1]: Leaving directory `C:/temp/mk/subdir'
VAR_EXPORTED: I am exported VAR_LOCAL: I am not exported

ifdef

ifdef var
  foo
  bar
endif
ifdef tests if a variable has a non empty has been defined. It is true even if the value of the variable is the empty string.

ifeq

ifeq is one of the four conditional directives. 
ifeq (arg1, arg2)
ifeq 'arg1' 'arg2'
ifeq "arg1" "arg2"
ifeq "arg1" 'arg2'
ifeq 'arg1' "arg2"
See also Test if a variable has non empty content.

ifdef

Quite the opposite of ifdef.

ifneq

, anchor=>'ifneq')
ifeq is one of the four conditional directives. 
ifneq (arg1, arg2)
ifneq 'arg1' 'arg2'
ifneq "arg1" "arg2"
ifneq "arg1" 'arg2'
ifneq 'arg1' "arg2"

include

include filename
include filename1 filename2 .. filenameN
include filename1 filename2 .. *glob
Includes the indictated files. Does globbing, if * is used.
If a specified does not start with slash and is not found in the current directory, the directories specified with the -I option are searched. Then the directories
  • prefix/include
    prefix normally being /usr/local
  • /usr/gnu/include
  • /usr/local/include
  • /usr/include
If a file cannot be found in any of these directories, a warning is issued. The warning can be supressed if the include directive is prepended with a hyphen: 
-include file_needs_not_exist
sinclude is a synonym for -include.

override

vpath

vpath pattern directories
Searches in directories for files that match pattern. directories can contain multiple directories, seperated by : or space. (; on windows systems)
The wildcard is %, not *.
The following example searches in ./src for *.c files and ./header for *.h files: 
vpath %.h ./header
vpath %.c ./src
See also VPATH.

Conditions

There are four conditional directives: 
conditional-directive
  foo
  bar
endif

conditional-directive
  foo
  bar
else
  quak
  muh
endif