Macro Processing Changes

A macro value can now be of virtually any length. Whereas in earlier versions only trailing white space was stripped from a macro value, this version strips off both leading and trailing white space characters.

Macros: Definition, Substitution, and Suffix Replacement

New Append Operator

+=

This is the new append operator that appends a SPACE followed by a word or words, onto the existing value of the macro.

Conditional Macro Definitions

:=

This is the conditional macro definitions operator that indicates a conditional (targetwise) macro definition. A makefile entry of the form:

target := macro = value

indicates that macro takes the indicated value while processing target and its dependencies.

Patterns in Conditional Macros

make recognizes the % wild card pattern in the target portion of a conditional macro definition. For instance:

profile_% := CFLAGS += -pg

would modify the CFLAGS macro for all targets having the `profile_' prefix. Pattern replacements can be used within the value of a conditional definition. For instance:

profile_% := OBJECTS = $(SOURCES:%.c=profile_%.o)

applies the profile_ prefix and .o suffix to the basename of every .c file in the SOURCES list (value).

Suffix Replacement Precedence

Substring replacement now takes place following expansion of the macro being referenced. Previous versions of make applied the substitution first, with results that were counterintuitive.

Nested Macro References

make now expands inner references before parsing the outer reference. A nested reference as in this example:

CFLAGS-g = -I../include
  OPTION = -g
  $(CFLAGS$(OPTION))

now yields the value -I../include , rather than a null value, as it would have in previous versions.

Cross-Compilation Macros

The predefined macros HOST_ARCH and TARGET_ARCH are available for use in cross-compilations. By default, the arch macros are set to the value returned by the arch command.

Shell Command Output in Macros

A definition of the form:

MACRO :sh = command

sets the value of MACRO to the standard output of the indicated command, NEWLINE characters being replaced with SPACE characters. The command is performed just once, when the definition is read. Standard error output is ignored, and make halts with an error if the command returns a non-zero exit status.

A macro reference of the form:

$(MACRO :sh)

expands to the output of the command line stored in the value of MACRO, whenever the reference is evaluated. NEWLINE characters are replaced with SPACE characters, standard error output is ignored, and make halts with an error if the command returns a non-zero exit status.