make: Features
14 Features of GNU 'make'
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Here is a summary of the features of GNU 'make', for comparison with and
credit to other versions of 'make'. We consider the features of 'make'
in 4.2 BSD systems as a baseline. If you are concerned with writing
portable makefiles, you should not use the features of 'make' listed
here, nor the ones in 
Missing.
Many features come from the version of 'make' in System V.
* The 'VPATH' variable and its special meaning. Searching
Directories for Prerequisites Directory Search. This feature
exists in System V 'make', but is undocumented. It is documented
in 4.3 BSD 'make' (which says it mimics System V's 'VPATH'
feature).
* Included makefiles. Including Other Makefiles Include.
Allowing multiple files to be included with a single directive is a
GNU extension.
* Variables are read from and communicated via the environment.
Variables from the Environment Environment.
* Options passed through the variable 'MAKEFLAGS' to recursive
invocations of 'make'. Communicating Options to a
Sub-'make' Options/Recursion.
* The automatic variable '$%' is set to the member name in an archive
reference. Automatic Variables.
* The automatic variables '$@', '$*', '$<', '$%', and '$?' have
corresponding forms like '$(@F)' and '$(@D)'. We have generalized
this to '$^' as an obvious extension. Automatic Variables.
* Substitution variable references. Basics of Variable
References Reference.
* The command line options '-b' and '-m', accepted and ignored. In
System V 'make', these options actually do something.
* Execution of recursive commands to run 'make' via the variable
'MAKE' even if '-n', '-q' or '-t' is specified. Recursive
Use of 'make' Recursion.
* Support for suffix '.a' in suffix rules. Archive Suffix
Rules. This feature is obsolete in GNU 'make', because the
general feature of rule chaining (Chains of Implicit Rules
Chained Rules.) allows one pattern rule for installing members in
an archive (Archive Update) to be sufficient.
* The arrangement of lines and backslash/newline combinations in
recipes is retained when the recipes are printed, so they appear as
they do in the makefile, except for the stripping of initial
whitespace.
The following features were inspired by various other versions of
'make'. In some cases it is unclear exactly which versions inspired
which others.
* Pattern rules using '%'. This has been implemented in several
versions of 'make'. We're not sure who invented it first, but it's
been spread around a bit. Defining and Redefining Pattern
Rules Pattern Rules.
* Rule chaining and implicit intermediate files. This was
implemented by Stu Feldman in his version of 'make' for AT&T Eighth
Edition Research Unix, and later by Andrew Hume of AT&T Bell Labs
in his 'mk' program (where he terms it "transitive closure"). We
do not really know if we got this from either of them or thought it
up ourselves at the same time. Chains of Implicit Rules
Chained Rules.
* The automatic variable '$^' containing a list of all prerequisites
of the current target. We did not invent this, but we have no idea
who did. Automatic Variables. The automatic variable '$+'
is a simple extension of '$^'.
* The "what if" flag ('-W' in GNU 'make') was (as far as we know)
invented by Andrew Hume in 'mk'. Instead of Executing
Recipes Instead of Execution.
* The concept of doing several things at once (parallelism) exists in
many incarnations of 'make' and similar programs, though not in the
System V or BSD implementations. Recipe Execution
Execution.
* A number of different build tools that support parallelism also
support collecting output and displaying as a single block.
Output During Parallel Execution Parallel Output.
* Modified variable references using pattern substitution come from
SunOS 4. Basics of Variable References Reference. This
functionality was provided in GNU 'make' by the 'patsubst' function
before the alternate syntax was implemented for compatibility with
SunOS 4. It is not altogether clear who inspired whom, since GNU
'make' had 'patsubst' before SunOS 4 was released.
* The special significance of '+' characters preceding recipe lines
(Instead of Executing Recipes Instead of Execution.) is
mandated by 'IEEE Standard 1003.2-1992' (POSIX.2).
* The '+=' syntax to append to the value of a variable comes from
SunOS 4 'make'. Appending More Text to Variables Appending.
* The syntax 'ARCHIVE(MEM1 MEM2...)' to list multiple members in a
single archive file comes from SunOS 4 'make'. Archive
Members.
* The '-include' directive to include makefiles with no error for a
nonexistent file comes from SunOS 4 'make'. (But note that SunOS 4
'make' does not allow multiple makefiles to be specified in one
'-include' directive.) The same feature appears with the name
'sinclude' in SGI 'make' and perhaps others.
* The '!=' shell assignment operator exists in many BSD of 'make' and
is purposefully implemented here to behave identically to those
implementations.
* Various build management tools are implemented using scripting
languages such as Perl or Python and thus provide a natural
embedded scripting language, similar to GNU 'make''s integration of
GNU Guile.
The remaining features are inventions new in GNU 'make':
* Use the '-v' or '--version' option to print version and copyright
information.
* Use the '-h' or '--help' option to summarize the options to 'make'.
* Simply-expanded variables. The Two Flavors of Variables
Flavors.
* Pass command line variable assignments automatically through the
variable 'MAKE' to recursive 'make' invocations. Recursive
Use of 'make' Recursion.
* Use the '-C' or '--directory' command option to change directory.
Summary of Options Options Summary.
* Make verbatim variable definitions with 'define'. Defining
Multi-Line Variables Multi-Line.
* Declare phony targets with the special target '.PHONY'.
Andrew Hume of AT&T Bell Labs implemented a similar feature with a
different syntax in his 'mk' program. This seems to be a case of
parallel discovery. Phony Targets Phony Targets.
* Manipulate text by calling functions. Functions for
Transforming Text Functions.
* Use the '-o' or '--old-file' option to pretend a file's
modification-time is old. Avoiding Recompilation of Some
Files Avoiding Compilation.
* Conditional execution.
This feature has been implemented numerous times in various
versions of 'make'; it seems a natural extension derived from the
features of the C preprocessor and similar macro languages and is
not a revolutionary concept. Conditional Parts of Makefiles
Conditionals.
* Specify a search path for included makefiles. Including
Other Makefiles Include.
* Specify extra makefiles to read with an environment variable.
The Variable 'MAKEFILES' MAKEFILES Variable.
* Strip leading sequences of './' from file names, so that './FILE'
and 'FILE' are considered to be the same file.
* Use a special search method for library prerequisites written in
the form '-lNAME'. Directory Search for Link Libraries
Libraries/Search.
* Allow suffixes for suffix rules (Old-Fashioned Suffix Rules
Suffix Rules.) to contain any characters. In other versions of
'make', they must begin with '.' and not contain any '/'
characters.
* Keep track of the current level of 'make' recursion using the
variable 'MAKELEVEL'. Recursive Use of 'make' Recursion.
* Provide any goals given on the command line in the variable
'MAKECMDGOALS'. Arguments to Specify the Goals Goals.
* Specify static pattern rules. Static Pattern Rules Static
Pattern.
* Provide selective 'vpath' search. Searching Directories for
Prerequisites Directory Search.
* Provide computed variable references. Basics of Variable
References Reference.
* Update makefiles. How Makefiles Are Remade Remaking
Makefiles. System V 'make' has a very, very limited form of this
functionality in that it will check out SCCS files for makefiles.
* Various new built-in implicit rules. Catalogue of Built-In
Rules Catalogue of Rules.
* Load dynamic objects which can modify the behavior of 'make'.
Loading Dynamic Objects Loading Objects.
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