make-05.html

unix make 文档

<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">-l 2.5</span></i></b></p>
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它的意思是告诉</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">当系统平均负荷高于</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">2.5</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">时，不再启动任何执行命令的子任务。不带浮点数的“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-l</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”选项用于取消前面通“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-l</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”给定的负荷限制。</span></p>
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更为准确一点就是：每一次，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">在启动一项任务之前（当前系统至少存在</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">的子任务正在运行）。首先</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">会检查当前系统的负荷；如果当前系统的负荷高于通过“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-l</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”选项指定的值，那么</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">就不会在其他任务完成之前启动任何任务。缺省情况下没有负荷限制。</span></p>
<h2><a name="_gnu_make_5.4"><span style="font-size: 14pt" lang="en-us"><b>5</b></span><b><span lang="EN-US" style="font-size: 14.0pt">.4<span style="font-style: normal; font-variant: normal; font-weight: normal; font-size: 7.0pt; font-family: Times New Roman">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
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命令执行的错误</span></a></h2>
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通常；规则中的命令在运行结束后，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">会检测命令执行的返回状态，如果返回成功，那么就启动另外一个子</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">shell</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">来执行下一条命令。规则中的所有命令执行完成之后，这个规则就执行完成了。如果一个规则中的某一个命令出错（返回非</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">0</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">状态），</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">就会放弃对当前规则后续命令的执行，也有可能会终止所有规则的执行。</span></p>
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一些情况下，规则中一个命令的执行失败并不代表规则执行的错误。例如我们使用“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">mkdir</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”命令来确保存在一个目录。当此目录不存在使我们就建立这个目录，当目录存在时那么“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">mkdir</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”就会执行失败。其实我们并不希望</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">mkdir</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">在执行失败后终止规则的执行。为了忽略一些无关命令执行失败的情况，我们可以在命令之前加一个减号“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”（在</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">[Tab]</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">字符之后），来告诉</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">忽略此命令的执行失败。命令中的“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”号会在</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">shell</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">解析并执行此命令之前被去掉，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">shell</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">所解释的只是纯粹的命令，“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”字符是由</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">来处理的。例如对于“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">clean</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”目标我们就可以这么写：</span></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">clean:</span></i></b></p>
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<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">-rm&nbsp; *.o</span></i></b></p>
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&nbsp;</span></p>
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其含义是：即使执行“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">rm</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”删除文件失败，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">也继续执行。</span></p>
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在执行</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">时，如果使用命令行选项“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-i</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”或者“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">—ignore-errors</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”，</span><span style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">
<span lang="EN-US">make</span></span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">将忽略所有规则中命令执行的错误。没有依赖的特殊目标“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">.IGNORE</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”在</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">Makefile</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">中有同样的效果。但是“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">.IGNORE</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”的方式已经很少使用，因为它没有在命令行之前使用“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”的方式灵活。</span></p>
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当使用</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">的“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-i</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”选项或者使用“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”字符来忽略命令执行的错误时，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">始终把命令的执行结果作为成功来对待。但会提示错误信息，同时提示这个错误被忽略。</span></p>
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当不使用这种方式来通知</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">忽略命令执行的错误时，那么在错误发生时，就意味着定义这个命令规则的目标不能被正确重建，同样，和此目标相关的其它目标也不会被正确重建。由于先决条件不能建立，那么后续的命令将不会被执行。</span></p>
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在发生这样情况时，通常</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">会立刻退出并返回一个非</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">0</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">状态，表示执行失败。像对待命令执行的错误一样，我们可以使用</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">的命令行选项“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-k</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”或者“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">--keep-going</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”来通知</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">，在出现错误时不立即退出，而是继续后续命令的执行。直到无法继续执行命令时才异常退出。例如：使用“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-k</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”参数，在重建一个</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">.o</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">文件目标时出现错误，</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">不会立即退出。虽然</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">已经知道因为这个错误而无法完成终极目标的重建，但还是继续完成其它后续的依赖文件的重建。直到执行最后链接时才错误退出。</span></p>
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一般</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">的“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-k</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”参数在实际应用中，主要用途是：当同时修改了工程中的多个文件后，“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-k</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”参数可以帮助我们确认对那些文件的修改是正确的（可以被编译），那些文件的修改是不正确的（不能正确编译）。例如我们修改了工程中的</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">20</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">个源文件，修改完成之后使用带“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">-k</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”参数的</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">make</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">，它可以一次性找出修改的</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">20</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">个文件中哪些是不能被编译。</span></p>
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通常情况下，执行失败的命令一旦改变了它所在规则的目标文件，则这个改变了的目标可能就不是一个被正确重建的文件。但是这个文件的时间戳已经被更新过了（这种情况也会发生在使用一个信