/usr/share/doc/make-doc/make.html/Features.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This file documents the GNU make utility, which determines
automatically which pieces of a large program need to be recompiled,
and issues the commands to recompile them.

This is Edition 0.74, last updated 21 May 2016,
of The GNU Make Manual, for GNU make version 4.2.1.

Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
1996, 1997, 1998, 1999, 2000, 2002, 2003, 2004, 2005, 2006, 2007,
2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016 Free Software
Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being "A GNU Manual,"
and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled "GNU Free Documentation
License."

(a) The FSF's Back-Cover Text is: "You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom." -->
<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Features (GNU make)</title>

<meta name="description" content="Features (GNU make)">
<meta name="keywords" content="Features (GNU make)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="index.html#Top" rel="up" title="Top">
<link href="Missing.html#Missing" rel="next" title="Missing">
<link href="Integrating-make.html#Terminal-Output" rel="prev" title="Terminal Output">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Features"></a>
<div class="header">
<p>
Next: <a href="Missing.html#Missing" accesskey="n" rel="next">Missing</a>, Previous: <a href="Integrating-make.html#Integrating-make" accesskey="p" rel="prev">Integrating make</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<a name="Features-of-GNU-make"></a>
<h2 class="chapter">14 Features of GNU <code>make</code></h2>
<a name="index-features-of-GNU-make"></a>
<a name="index-portability"></a>
<a name="index-compatibility"></a>

<p>Here is a summary of the features of GNU <code>make</code>, for comparison
with and credit to other versions of <code>make</code>.  We consider the
features of <code>make</code> in 4.2 BSD systems as a baseline.  If you are
concerned with writing portable makefiles, you should not use the
features of <code>make</code> listed here, nor the ones in <a href="Missing.html#Missing">Missing</a>.
</p>
<p>Many features come from the version of <code>make</code> in System V.
</p>
<ul>
<li> The <code>VPATH</code> variable and its special meaning.
See <a href="Rules.html#Directory-Search">Searching Directories for Prerequisites</a>.
This feature exists in System V <code>make</code>, but is undocumented.
It is documented in 4.3 BSD <code>make</code> (which says it mimics System V&rsquo;s
<code>VPATH</code> feature).

</li><li> Included makefiles.  See <a href="Makefiles.html#Include">Including Other Makefiles</a>.
Allowing multiple files to be included with a single directive is a GNU
extension.

</li><li> Variables are read from and communicated via the environment.
See <a href="Using-Variables.html#Environment">Variables from the Environment</a>.

</li><li> Options passed through the variable <code>MAKEFLAGS</code> to recursive
invocations of <code>make</code>.
See <a href="Recipes.html#Options_002fRecursion">Communicating Options to a Sub-<code>make</code></a>.

</li><li> The automatic variable <code>$%</code> is set to the member name
in an archive reference.  See <a href="Implicit-Rules.html#Automatic-Variables">Automatic Variables</a>.

</li><li> The automatic variables <code>$@</code>, <code>$*</code>, <code>$&lt;</code>, <code>$%</code>,
and <code>$?</code> have corresponding forms like <code>$(@F)</code> and
<code>$(@D)</code>.  We have generalized this to <code>$^</code> as an obvious
extension.  See <a href="Implicit-Rules.html#Automatic-Variables">Automatic Variables</a>.

</li><li> Substitution variable references.
See <a href="Using-Variables.html#Reference">Basics of Variable References</a>.

</li><li> The command line options &lsquo;<samp>-b</samp>&rsquo; and &lsquo;<samp>-m</samp>&rsquo;, accepted and
ignored.  In System V <code>make</code>, these options actually do something.

</li><li> Execution of recursive commands to run <code>make</code> via the variable
<code>MAKE</code> even if &lsquo;<samp>-n</samp>&rsquo;, &lsquo;<samp>-q</samp>&rsquo; or &lsquo;<samp>-t</samp>&rsquo; is specified.
See <a href="Recipes.html#Recursion">Recursive Use of <code>make</code></a>.

</li><li> Support for suffix &lsquo;<samp>.a</samp>&rsquo; in suffix rules.  See <a href="Archives.html#Archive-Suffix-Rules">Archive Suffix Rules</a>.  This feature is obsolete in GNU <code>make</code>, because the
general feature of rule chaining (see <a href="Implicit-Rules.html#Chained-Rules">Chains of
Implicit Rules</a>) allows one pattern rule for installing members in an
archive (see <a href="Archives.html#Archive-Update">Archive Update</a>) to be sufficient.

</li><li> 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.
</li></ul>

<p>The following features were inspired by various other versions of
<code>make</code>.  In some cases it is unclear exactly which versions inspired
which others.
</p>
<ul>
<li> Pattern rules using &lsquo;<samp>%</samp>&rsquo;.
This has been implemented in several versions of <code>make</code>.
We&rsquo;re not sure who invented it first, but it&rsquo;s been spread around a bit.
See <a href="Implicit-Rules.html#Pattern-Rules">Defining and Redefining Pattern Rules</a>.

</li><li> Rule chaining and implicit intermediate files.
This was implemented by Stu Feldman in his version of <code>make</code>
for AT&amp;T Eighth Edition Research Unix, and later by Andrew Hume of
AT&amp;T Bell Labs in his <code>mk</code> program (where he terms it
&ldquo;transitive closure&rdquo;).  We do not really know if
we got this from either of them or thought it up ourselves at the
same time.  See <a href="Implicit-Rules.html#Chained-Rules">Chains of Implicit Rules</a>.

</li><li> The automatic variable <code>$^</code> containing a list of all prerequisites
of the current target.  We did not invent this, but we have no idea who
did.  See <a href="Implicit-Rules.html#Automatic-Variables">Automatic Variables</a>.  The automatic variable
<code>$+</code> is a simple extension of <code>$^</code>.

</li><li> The &ldquo;what if&rdquo; flag (&lsquo;<samp>-W</samp>&rsquo; in GNU <code>make</code>) was (as far as we know)
invented by Andrew Hume in <code>mk</code>.
See <a href="Running.html#Instead-of-Execution">Instead of Executing Recipes</a>.

</li><li> The concept of doing several things at once (parallelism) exists in
many incarnations of <code>make</code> and similar programs, though not in the
System V or BSD implementations.  See <a href="Recipes.html#Execution">Recipe Execution</a>.

</li><li> A number of different build tools that support parallelism also
support collecting output and displaying as a single block.
See <a href="Recipes.html#Parallel-Output">Output During Parallel Execution</a>.

</li><li> Modified variable references using pattern substitution come from
SunOS 4.  See <a href="Using-Variables.html#Reference">Basics of Variable References</a>.
This functionality was provided in GNU <code>make</code> by the
<code>patsubst</code> function before the alternate syntax was implemented
for compatibility with SunOS 4.  It is not altogether clear who
inspired whom, since GNU <code>make</code> had <code>patsubst</code> before SunOS
4 was released.

</li><li> The special significance of &lsquo;<samp>+</samp>&rsquo; characters preceding recipe lines
(see <a href="Running.html#Instead-of-Execution">Instead of Executing Recipes</a>) is
mandated by <cite>IEEE Standard 1003.2-1992</cite> (POSIX.2).

</li><li> The &lsquo;<samp>+=</samp>&rsquo; syntax to append to the value of a variable comes from SunOS
4 <code>make</code>.  See <a href="Using-Variables.html#Appending">Appending More Text to Variables</a>.

</li><li> The syntax &lsquo;<samp><var>archive</var>(<var>mem1</var>&nbsp;<var>mem2</var>&hellip;)</samp>&rsquo;<!-- /@w --> to list
multiple members in a single archive file comes from SunOS 4 <code>make</code>.
See <a href="Archives.html#Archive-Members">Archive Members</a>.

</li><li> The <code>-include</code> directive to include makefiles with no error for a
nonexistent file comes from SunOS 4 <code>make</code>.  (But note that SunOS 4
<code>make</code> does not allow multiple makefiles to be specified in one
<code>-include</code> directive.)  The same feature appears with the name
<code>sinclude</code> in SGI <code>make</code> and perhaps others.

</li><li> The <code>!=</code> shell assignment operator exists in many BSD of
<code>make</code> and is purposefully implemented here to behave identically
to those implementations.

</li><li> 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 <code>make</code>&rsquo;s integration of GNU
Guile.
</li></ul>

<p>The remaining features are inventions new in GNU <code>make</code>:
</p>
<ul>
<li> Use the &lsquo;<samp>-v</samp>&rsquo; or &lsquo;<samp>--version</samp>&rsquo; option to print version and
copyright information.

</li><li> Use the &lsquo;<samp>-h</samp>&rsquo; or &lsquo;<samp>--help</samp>&rsquo; option to summarize the options to
<code>make</code>.

</li><li> Simply-expanded variables.  See <a href="Using-Variables.html#Flavors">The Two Flavors of Variables</a>.

</li><li> Pass command line variable assignments automatically through the
variable <code>MAKE</code> to recursive <code>make</code> invocations.
See <a href="Recipes.html#Recursion">Recursive Use of <code>make</code></a>.

</li><li> Use the &lsquo;<samp>-C</samp>&rsquo; or &lsquo;<samp>--directory</samp>&rsquo; command option to change
directory.  See <a href="Running.html#Options-Summary">Summary of Options</a>.

</li><li> Make verbatim variable definitions with <code>define</code>.
See <a href="Using-Variables.html#Multi_002dLine">Defining Multi-Line Variables</a>.

</li><li> Declare phony targets with the special target <code>.PHONY</code>.

<p>Andrew Hume of AT&amp;T Bell Labs implemented a similar feature with a
different syntax in his <code>mk</code> program.  This seems to be a case of
parallel discovery.  See <a href="Rules.html#Phony-Targets">Phony Targets</a>.
</p>
</li><li> Manipulate text by calling functions.
See <a href="Functions.html#Functions">Functions for Transforming Text</a>.

</li><li> Use the &lsquo;<samp>-o</samp>&rsquo; or &lsquo;<samp>--old-file</samp>&rsquo;
option to pretend a file&rsquo;s modification-time is old.
See <a href="Running.html#Avoiding-Compilation">Avoiding Recompilation of Some Files</a>.

</li><li> Conditional execution.

<p>This feature has been implemented numerous times in various versions
of <code>make</code>; it seems a natural extension derived from the features
of the C preprocessor and similar macro languages and is not a
revolutionary concept.  See <a href="Conditionals.html#Conditionals">Conditional Parts of Makefiles</a>.
</p>
</li><li> Specify a search path for included makefiles.
See <a href="Makefiles.html#Include">Including Other Makefiles</a>.

</li><li> Specify extra makefiles to read with an environment variable.
See <a href="Makefiles.html#MAKEFILES-Variable">The Variable <code>MAKEFILES</code></a>.

</li><li> Strip leading sequences of &lsquo;<samp>./</samp>&rsquo; from file names, so that
<samp>./<var>file</var></samp> and <samp><var>file</var></samp> are considered to be the
same file.

</li><li> Use a special search method for library prerequisites written in the
form &lsquo;<samp>-l<var>name</var></samp>&rsquo;.
See <a href="Rules.html#Libraries_002fSearch">Directory Search for Link Libraries</a>.

</li><li> Allow suffixes for suffix rules
(see <a href="Implicit-Rules.html#Suffix-Rules">Old-Fashioned Suffix Rules</a>) to contain any
characters.  In other versions of <code>make</code>, they must begin with
&lsquo;<samp>.</samp>&rsquo; and not contain any &lsquo;<samp>/</samp>&rsquo; characters.

</li><li> Keep track of the current level of <code>make</code> recursion using the
variable <code>MAKELEVEL</code>.  See <a href="Recipes.html#Recursion">Recursive Use of <code>make</code></a>.

</li><li> Provide any goals given on the command line in the variable
<code>MAKECMDGOALS</code>.  See <a href="Running.html#Goals">Arguments to Specify the Goals</a>.

</li><li> Specify static pattern rules.  See <a href="Rules.html#Static-Pattern">Static Pattern Rules</a>.

</li><li> Provide selective <code>vpath</code> search.
See <a href="Rules.html#Directory-Search">Searching Directories for Prerequisites</a>.

</li><li> Provide computed variable references.
See <a href="Using-Variables.html#Reference">Basics of Variable References</a>.

</li><li> Update makefiles.  See <a href="Makefiles.html#Remaking-Makefiles">How Makefiles Are Remade</a>.
System V <code>make</code> has a very, very limited form of this
functionality in that it will check out SCCS files for makefiles.

</li><li> Various new built-in implicit rules.
See <a href="Implicit-Rules.html#Catalogue-of-Rules">Catalogue of Built-In Rules</a>.

</li><li> Load dynamic objects which can modify the behavior of <code>make</code>.
See <a href="Extending-make.html#Loading-Objects">Loading Dynamic Objects</a>.
</li></ul>

<hr>
<div class="header">
<p>
Next: <a href="Missing.html#Missing" accesskey="n" rel="next">Missing</a>, Previous: <a href="Integrating-make.html#Integrating-make" accesskey="p" rel="prev">Integrating make</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>



</body>
</html>
make-doc 4.2.1-1 / usr / share / doc / make-doc / make.html / Features.html
