make-07.html

unix make 文档

通常我们会使用它来判断一个变量的值是否为空（不是任何字符）。参数值可能是通过引用变量或者函数得到的，因而在展开过程中可能造成参数值中包含空字符（空格等）。一般在这种情况时我们使用</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">strip</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”函数来对它变量的值进行处理，去掉其中的空字符。格式为：</span></p>
<p class="MsoNormal" style="text-indent: 20.5pt">
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">&nbsp;</span></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">ifeq ($(strip 
$(foo)),)</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">TEXT-IF-EMPTY</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">endif</span></i></b></p>
<p class="MsoNormal" style="text-indent: 20.5pt">
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">&nbsp;</span></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
这样，即就是在“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">$(foo)</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”中存在若干前导和结尾空格，“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">TEXT-IF-EMPTY</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”也会被作为</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">需要执行的一部分。</span></p>
<h3><a name="_gnu_make_7.2.2"><span lang="en-us">7</span><span lang="EN-US">.2.2<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;&nbsp;
</span></span><span style="font-family: 黑体">关键字“</span><span lang="EN-US">ifneq</span></a><span style="font-family: 黑体">”</span></h3>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; text-indent: 24.0pt; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
此关键字是用来判断参数是否不相等，格式为：</span></p>
<p class="MsoNormal" style="text-indent: 20.6pt"><b>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial; color: blue">`ifneq 
(ARG1, ARG2)'</span></b></p>
<p class="MsoNormal" style="text-indent: 20.6pt"><b>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial; color: blue">`ifneq 
'ARG1' 'ARG2''</span></b></p>
<p class="MsoNormal" style="text-indent: 20.6pt"><b>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial; color: blue">`ifneq 
&quot;ARG1&quot; &quot;ARG2&quot;'</span></b></p>
<p class="MsoNormal" style="text-indent: 20.6pt"><b>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial; color: blue">`ifneq 
&quot;ARG1&quot; 'ARG2''</span></b></p>
<p class="MsoNormal" style="text-indent: 20.6pt"><b>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial; color: blue">`ifneq 
'ARG1' &quot;ARG2&quot;'</span></b></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; text-indent: 24.0pt; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">
&nbsp;</span></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
关键字“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifneq</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”实现的条件判断语句和“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifeq</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”相反。首先替换并展开“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ARG1</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”和“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ARG1</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”，对它们的值进行比较。如果不相同（条件为真）则将“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">TEXT-IF-TRUE</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”作为</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">要执行的一部分，否则将“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">TEXT-IF-FALSE</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”作为</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">要执行的一部分。</span></p>
<h3><a name="_gnu_make_7.2.3"><span lang="en-us">7</span><span lang="EN-US">.2.3<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;&nbsp;
</span></span><span style="font-family: 黑体">关键字“</span><span lang="EN-US">ifdef</span><span style="font-family: 黑体">”</span></a></h3>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; text-indent: 24.0pt; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
关键字“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”用来判断一个变量是否已经定义。格式为：</span></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; text-indent: 24.1pt; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<b>
<span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: blue">
`ifdef VARIABLE-NAME'</span></b><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">
</span></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
如果变量“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">VAEIABLE_NAME</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”的值非空（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">中没有定义的变量的值为空），那么表达式为真，将“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">TEXT-IF-TRUE</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”作为</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">要执行的一部分。否则，表达式为假，如果存在“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">TEXT-IF-FALSE</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”，就将它作为</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">要执行一部分。当一个变量没有被定义时，它的值为空。“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">VARIABLE-NAME</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”可以是变量或者函数的引用。</span></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; text-indent: 24.0pt; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
对于“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”需要说明的是：</span><b><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">只是测试一个变量是否有值，不会对变量进行替换展开来判断变量的值是否为空。对于变量“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">VARIABLE-NAME</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”，除了“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">VARIABLE-NAME=</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”这种情况以外，使用其它方式对它的定义都会使“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”返回真。就是说，即使我们通过其它方式（比如，定义它的值引用了其它的变量）给它赋了一个空值，“</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">ifdef</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">”也会返回真。我们来看一个例子</span></b><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">：</span></p>
<p class="MsoNormal" style="text-indent: 20.5pt">
<span style="font-size: 12.0pt; font-family: 楷体_GB2312; color: black">例</span><span lang="EN-US" style="font-size: 12.0pt; font-family: Arial; color: black">1</span><span style="font-size: 12.0pt; font-family: 楷体_GB2312; color: black">：</span></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">bar =</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">foo = $(bar)</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">ifdef foo</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">frobozz = yes</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">else</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">frobozz = no</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">endif</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">&nbsp;</span></i></b></p>
<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; text-indent: 24.0pt; line-height: 150%; text-autospace: ideograph-numeric ideograph-other">
<span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">
例</span><span lang="EN-US" style="font-size: 12.0pt; line-height: 150%; font-family: Arial; color: black">2</span><span style="font-size: 12.0pt; line-height: 150%; font-family: 楷体_GB2312; color: black">：</span></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>
<span lang="EN-US" style="font-size: 12.0pt; font-family: Arial">foo =</span></i></b></p>
<p class="MsoNormal" style="text-indent: 13.85pt; margin-left: 29.95pt"><b><i>