Linux 的make及makefile文件格式

代码变成可执行文件，叫做编译（compile）；先编译这个，还是先编译那个（即编译的安排），叫做构建（build）。

Make是最常用的构建工具，诞生于1977年，主要用于C语言的项目。但是实际上 ，任何只要某个文件有变化，就要重新构建的项目，都可以用Make构建。

本文介绍Make命令的用法，从简单的讲起，不需要任何基础，只要会使用命令行，就能看懂。我的参考资料主要是Isaac Schlueter的《Makefile文件教程》和《GNU Make手册》。

（题图：摄于博兹贾阿达岛，土耳其，2013年7月）

一、Make的概念

Make这个词，英语的意思是"制作"。Make命令直接用了这个意思，就是要做出某个文件。比如，要做出文件a.txt，就可以执行下面的命令。

<code class=" language-bash">$ make a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

但是，如果你真的输入这条命令，它并不会起作用。因为Make命令本身并不知道，如何做出a.txt，需要有人告诉它，如何调用其他命令完成这个目标。

比如，假设文件 a.txt 依赖于 b.txt 和 c.txt ，是后面两个文件连接（cat命令）的产物。那么，make 需要知道下面的规则。

<code class=" language-bash">a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt    cat b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span> a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

也就是说，make a.txt 这条命令的背后，实际上分成两步：第一步，确认 b.txt 和 c.txt 必须已经存在，第二步使用 cat 命令 将这个两个文件合并，输出为新文件。

像这样的规则，都写在一个叫做Makefile的文件中，Make命令依赖这个文件进行构建。Makefile文件也可以写为makefile， 或者用命令行参数指定为其他文件名。

<code class=" language-bash">$ make <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>f rules<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 或者</span>$ make <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">--</span>file<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>rules<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

上面代码指定make命令依据rules.txt文件中的规则，进行构建。

总之，make只是一个根据指定的Shell命令进行构建的工具。它的规则很简单，你规定要构建哪个文件、它依赖哪些源文件，当那些文件有变动时，如何重新构建它。

二、Makefile文件的格式

构建规则都写在Makefile文件里面，要学会如何Make命令，就必须学会如何编写Makefile文件。

2.1 概述

Makefile文件由一系列规则（rules）构成。每条规则的形式如下。

<code class=" language-bash"><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);"><</span>target<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span> <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);"><</span>prerequisites<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span> <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">[</span>tab<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">]</span>  <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);"><</span>commands<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span></code>

上面第一行冒号前面的部分，叫做"目标"（target），冒号后面的部分叫做"前置条件"（prerequisites）；第二行必须由一个tab键起首，后面跟着"命令"（commands）。

"目标"是必需的，不可省略；"前置条件"和"命令"都是可选的，但是两者之中必须至少存在一个。

每条规则就明确两件事：构建目标的前置条件是什么，以及如何构建。下面就详细讲解，每条规则的这三个组成部分。

2.2 目标（target）

一个目标（target）就构成一条规则。目标通常是文件名，指明Make命令所要构建的对象，比如上文的 a.txt 。目标可以是一个文件名，也可以是多个文件名，之间用空格分隔。

除了文件名，目标还可以是某个操作的名字，这称为"伪目标"（phony target）。

<code class=" language-bash">clean<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>      rm <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">*</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o</code>

上面代码的目标是clean，它不是文件名，而是一个操作的名字，属于"伪目标 "，作用是删除对象文件。

<code class=" language-bash">$ make  clean</code>

但是，如果当前目录中，正好有一个文件叫做clean，那么这个命令不会执行。因为Make发现clean文件已经存在，就认为没有必要重新构建了，就不会执行指定的rm命令。

为了避免这种情况，可以明确声明clean是"伪目标"，写法如下。

<code class=" language-bash"><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>PHONY<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> cleanclean<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>        rm <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">*</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o temp</code>

声明clean是"伪目标"之后，make就不会去检查是否存在一个叫做clean的文件，而是每次运行都执行对应的命令。像.PHONY这样的内置目标名还有不少，可以查看手册。

如果Make命令运行时没有指定目标，默认会执行Makefile文件的第一个目标。

<code class=" language-bash">$ make</code>

上面代码执行Makefile文件的第一个目标。

2.3 前置条件（prerequisites）

前置条件通常是一组文件名，之间用空格分隔。它指定了"目标"是否重新构建的判断标准：只要有一个前置文件不存在，或者有过更新（前置文件的last-modification时间戳比目标的时间戳新），"目标"就需要重新构建。

<code class=" language-bash">result<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt    cp source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt result<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

上面代码中，构建 result.txt 的前置条件是 source.txt 。如果当前目录中，source.txt 已经存在，那么make result.txt可以正常运行，否则必须再写一条规则，来生成 source.txt 。

<code class=" language-bash">source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> <span class="token string" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(102, 153, 0);">"this is the source"</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span> source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

上面代码中，source.txt后面没有前置条件，就意味着它跟其他文件都无关，只要这个文件还不存在，每次调用make source.txt，它都会生成。

<code class=" language-bash">$ make result<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt$ make result<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

上面命令连续执行两次make result.txt。第一次执行会先新建 source.txt，然后再新建 result.txt。第二次执行，Make发现 source.txt 没有变动（时间戳晚于 result.txt），就不会执行任何操作，result.txt 也不会重新生成。

如果需要生成多个文件，往往采用下面的写法。

<code class=" language-bash">source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> file1 file2 file3</code>

上面代码中，source 是一个伪目标，只有三个前置文件，没有任何对应的命令。

<code class=" language-bash">$ make source</code>

执行make source命令后，就会一次性生成 file1，file2，file3 三个文件。这比下面的写法要方便很多。

<code class=" language-bash">$ make file1$ make file2$ make file3</code>

2.4 命令（commands）

命令（commands）表示如何更新目标文件，由一行或多行的Shell命令组成。它是构建"目标"的具体指令，它的运行结果通常就是生成目标文件。

每行命令之前必须有一个tab键。如果想用其他键，可以用内置变量.RECIPEPREFIX声明。

<code class=" language-bash"><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>RECIPEPREFIX <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span>all<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">></span> <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> Hello<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span> world</code>

上面代码用.RECIPEPREFIX指定，大于号（>）替代tab键。所以，每一行命令的起首变成了大于号，而不是tab键。

需要注意的是，每行命令在一个单独的shell中执行。这些Shell之间没有继承关系。

<code class=" language-bash">var<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>lost<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    export foo<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>bar    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> <span class="token string" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(102, 153, 0);">"foo=[$<span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$foo</span>]"</span></code>

上面代码执行后（make var-lost），取不到foo的值。因为两行命令在两个不同的进程执行。一个解决办法是将两行命令写在一行，中间用分号分隔。

<code class=" language-bash">var<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>kept<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    export foo<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>bar<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span> <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> <span class="token string" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(102, 153, 0);">"foo=[$<span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$foo</span>]"</span></code>

另一个解决办法是在换行符前加反斜杠转义。

<code class=" language-bash">var<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>kept<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    export foo<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>bar<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span> \    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> <span class="token string" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(102, 153, 0);">"foo=[$<span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$foo</span>]"</span></code>

最后一个方法是加上.ONESHELL:命令。

<code class=" language-bash"><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>ONESHELL<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>var<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>kept<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    export foo<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>bar<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span>     <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> <span class="token string" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(102, 153, 0);">"foo=[$<span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$foo</span>]"</span></code>

三、Makefile文件的语法

3.1 注释

井号（#）在Makefile中表示注释。

<code class=" language-bash"><span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这是注释</span>result<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt    <span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这是注释</span>    cp source<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt result<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt <span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这也是注释</span></code>

3.2 回声（echoing）

正常情况下，make会打印每条命令，然后再执行，这就叫做回声（echoing）。

<code class=" language-bash">test<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    <span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这是测试</span></code>

执行上面的规则，会得到下面的结果。

<code class=" language-bash">$ make test<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这是测试</span></code>

在命令的前面加上@，就可以关闭回声。

<code class=" language-bash">test<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    @<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这是测试</span></code>

现在再执行make test，就不会有任何输出。

由于在构建过程中，需要了解当前在执行哪条命令，所以通常只在注释和纯显示的echo命令前面加上@。

<code class=" language-bash">test<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    @<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 这是测试</span>    @<span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> TODO</code>

3.3 通配符

通配符（wildcard）用来指定一组符合条件的文件名。Makefile 的通配符与 Bash 一致，主要有星号（*）、问号（？）和 [...] 。比如， *.o 表示所有后缀名为o的文件。

<code class=" language-bash">clean<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>        rm <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>f <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">*</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o</code>

3.4 模式匹配

Make命令允许对文件名，进行类似正则运算的匹配，主要用到的匹配符是%。比如，假定当前目录下有 f1.c 和 f2.c 两个源码文件，需要将它们编译为对应的对象文件。

<code class=" language-bash"><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">%</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">%</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c</code>

等同于下面的写法。

<code class=" language-bash">f1<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> f1<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>cf2<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> f2<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c</code>

使用匹配符%，可以将大量同类型的文件，只用一条规则就完成构建。

3.5 变量和赋值符

Makefile 允许使用等号自定义变量。

<code class=" language-bash">txt <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> Hello Worldtest<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    @<span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

上面代码中，变量 txt 等于 Hello World。调用时，变量需要放在 $( ) 之中。

调用Shell变量，需要在美元符号前，再加一个美元符号，这是因为Make命令会对美元符号转义。

<code class=" language-bash">test<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    @<span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> $<span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$HOME</span></code>

有时，变量的值可能指向另一个变量。

<code class=" language-bash">v1 <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>v2<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

上面代码中，变量 v1 的值是另一个变量 v2。这时会产生一个问题，v1 的值到底在定义时扩展（静态扩展），还是在运行时扩展（动态扩展）？如果 v2 的值是动态的，这两种扩展方式的结果可能会差异很大。

为了解决类似问题，Makefile一共提供了四个赋值运算符 （=、:=、？=、+=），它们的区别请看StackOverflow。

<code class=" language-bash">VARIABLE <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> value<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 在执行时扩展，允许递归扩展。</span>VARIABLE <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> value<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 在定义时扩展。</span>VARIABLE <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">?</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> value<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 只有在该变量为空时才设置值。</span>VARIABLE <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">+</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> value<span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 将值追加到变量的尾端。</span></code>

3.6 内置变量（Implicit Variables）

Make命令提供一系列内置变量，比如，$(CC) 指向当前使用的编译器，$(MAKE) 指向当前使用的Make工具。这主要是为了跨平台的兼容性，详细的内置变量清单见手册。

<code class=" language-bash">output<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>CC<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>o output input<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c</code>

3.7 自动变量（Automatic Variables）

Make命令还提供一些自动变量，它们的值与当前规则有关。主要有以下几个。

（1）$@

$@指代当前目标，就是Make命令当前构建的那个目标。比如，make foo的 $@ 就指代foo。 

<code class=" language-bash">a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>     touch <span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$@</span></code>

等同于下面的写法。

<code class=" language-bash">a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    touch a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txtb<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    touch b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt</code>

（2）$<

$< 指代第一个前置条件。比如，规则为 t: p1 p2，那么$< 就指代p1。

<code class=" language-bash">a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt    cp $<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);"><</span> <span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$@</span> </code>

等同于下面的写法。

<code class=" language-bash">a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt    cp b<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt a<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt </code>

（3）$?

$? 指代比目标更新的所有前置条件，之间以空格分隔。比如，规则为 t: p1 p2，其中 p2 的时间戳比 t 新，$?就指代p2。

（4）$^

$^ 指代所有前置条件，之间以空格分隔。比如，规则为 t: p1 p2，那么 $^ 就指代 p1 p2 。

（5）$*

$* 指代匹配符 % 匹配的部分， 比如% 匹配 f1.txt 中的f1 ，$* 就表示 f1。

（6）$(@D) 和 $(@F)

$(@D) 和 $(@F) 分别指向 $@ 的目录名和文件名。比如，$@是 src/input.c，那么$(@D) 的值为 src ，$(@F) 的值为 input.c。

（7）$(<D) 和 $(<F)

$(<D) 和 $(<F) 分别指向 $< 的目录名和文件名。 

所有的自动变量清单，请看手册。下面是自动变量的一个例子。

<code class=" language-bash">dest<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">/</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">%</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> src<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">/</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">%</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt    @<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">[</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>d dest <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">]</span> <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">||</span> mkdir dest    cp $<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);"><</span> <span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$@</span></code>

上面代码将 src 目录下的 txt 文件，拷贝到 dest 目录下。首先判断 dest 目录是否存在，如果不存在就新建，然后，$< 指代前置文件（src/%.txt）， $@ 指代目标文件（dest/%.txt）。

3.8 判断和循环

Makefile使用 Bash 语法，完成判断和循环。

<code class=" language-bash">ifeq <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>CC<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>gcc<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span>  libs<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>libs_for_gcc<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">else</span>  libs<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span>$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>normal_libs<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span>endif</code>

上面代码判断当前编译器是否 gcc ，然后指定不同的库文件。

<code class=" language-bash">LIST <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> one two threeall<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">for</span> i <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">in</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>LIST<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span> <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">do</span> \        <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> $<span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$i</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span> \    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">done</span><span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 等同于</span>all<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">for</span> i <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">in</span> one two three<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span> <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">do</span> \        <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> <span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">$i</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">;</span> \    <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">done</span></code>

上面代码的运行结果。

<code class=" language-bash">onetwothree</code>

3.9 函数

Makefile 还可以使用函数，格式如下。

<code class=" language-bash">$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span><span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">function</span> arguments<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># 或者</span><span class="token property" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">${function arguments}</span></code>

Makefile提供了许多内置函数，可供调用。下面是几个常用的内置函数。

（1）shell 函数

shell 函数用来执行 shell 命令

<code class=" language-bash">srcfiles <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>shell <span class="token keyword" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(0, 119, 170);">echo</span> src<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">/</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">{</span><span class="token number" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">00</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span><span class="token number" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 0, 85);">99</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">}</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

（2）wildcard 函数

wildcard 函数用来在 Makefile 中，替换 Bash 的通配符。

<code class=" language-bash">srcfiles <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>wildcard src<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">/</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">*</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>txt<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

（3）subst 函数

subst 函数用来文本替换，格式如下。

<code class=" language-bash">$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>subst from<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>to<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>text<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

下面的例子将字符串"feet on the street"替换成"fEEt on the strEEt"。

<code class=" language-bash">$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>subst ee<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>EE<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>feet on the street<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

下面是一个稍微复杂的例子。

<code class=" language-bash">comma<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>empty<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span><span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># space变量用两个空变量作为标识符，当中是一个空格</span>space<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>empty<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>empty<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span>foo<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> a b cbar<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>subst $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>space<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>comma<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>foo<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span><span class="token comment" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(112, 128, 144);"># bar is now `a,b,c'.</span></code>

（4）patsubst函数

patsubst 函数用于模式匹配的替换，格式如下。

<code class=" language-bash">$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>patsubst pattern<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>replacement<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>text<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

下面的例子将文件名"x.c.c bar.c"，替换成"x.c.o bar.o"。

<code class=" language-bash">$<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>patsubst <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">%</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span><span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">%</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">,</span>x<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c bar<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

（5）替换后缀名

替换后缀名函数的写法是：变量名 + 冒号 + 后缀名替换规则。它实际上patsubst函数的一种简写形式。

<code class=" language-bash">min<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> $<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">(</span>OUTPUT<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>js<span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">=</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>min<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>js<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">)</span></code>

上面代码的意思是，将变量OUTPUT中的后缀名 .js 全部替换成 .min.js 。

四、Makefile 的实例

（1）执行多个目标

<code class=" language-bash"><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>PHONY<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> cleanall cleanobj cleandiffcleanall <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> cleanobj cleandiff        rm programcleanobj <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>        rm <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">*</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>ocleandiff <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>        rm <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">*</span><span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>diff</code>

上面代码可以调用不同目标，删除不同后缀名的文件，也可以调用一个目标（cleanall），删除所有指定类型的文件。

（2）编译C语言项目

<code class=" language-bash">edit <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> main<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o kbd<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o display<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o     cc <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>o edit main<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o kbd<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o display<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>omain<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> main<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c defs<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>h    cc <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>c main<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>ckbd<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> kbd<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c defs<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>h command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>h    cc <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>c kbd<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>ccommand<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c defs<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>h command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>h    cc <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>c command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>cdisplay<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> display<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>c defs<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>h    cc <span class="token operator" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(166, 127, 89);">-</span>c display<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>cclean <span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span>     rm edit main<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o kbd<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o command<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o display<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>o<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">.</span>PHONY<span class="token punctuation" style="margin: 0px; padding: 0px; list-style-type: none; border: none; color: rgb(153, 153, 153);">:</span> edit clean</code>

今天，Make命令的介绍就到这里。下一篇文章我会介绍，如何用 Make 来构建 Node.js 项目。