解释 makefile % 以及 $<和$@

发布于 2024-08-30 19:18:09 字数 711 浏览 1 评论 0 原文

xpi_built := $(build_dir)/$(install_rdf) \
             $(build_dir)/$(chrome_manifest) \
             $(chrome_jar_file) \
             $(default_prefs)

xpi_built_no_dir := $(subst $(build_dir)/,,$(xpi_built))

$(xpi_file): $(build_dir) $(xpi_built)
 @echo "Creating XPI file."
 cd $(build_dir); $(ZIP) ../$(xpi_file) $(xpi_built_no_dir)
 @echo "Creating XPI file. Done!"

$(build_dir)/%: %
 cp -f $< $@

$(build_dir):
 @if [ ! -x $(build_dir) ]; \
  then \
    mkdir $(build_dir); \
  fi

谁能给我解释一下这个 makefile 部分吗？对

$(build_dir)/%: % 以及 $< 和 $@ 指令
两个标签 $(build_dir ) 存在，我猜两者都执行了，但是按什么顺序执行？

原文

xpi_built := $(build_dir)/$(install_rdf) \
             $(build_dir)/$(chrome_manifest) \
             $(chrome_jar_file) \
             $(default_prefs)

xpi_built_no_dir := $(subst $(build_dir)/,,$(xpi_built))

$(xpi_file): $(build_dir) $(xpi_built)
 @echo "Creating XPI file."
 cd $(build_dir); $(ZIP) ../$(xpi_file) $(xpi_built_no_dir)
 @echo "Creating XPI file. Done!"

$(build_dir)/%: %
 cp -f lt; $@

$(build_dir):
 @if [ ! -x $(build_dir) ]; \
  then \
    mkdir $(build_dir); \
  fi

can anyone explain me this makefile part? particularly interested in

$(build_dir)/%: % as well as $< and $@ directives
two labels $(build_dir) exists, I guess both are executed, but in which order?

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温暖的光 2024-09-06 19:18:09

$(build_dir)/%: %
    cp -f lt; $@

这是一个静态模式规则，在其命令中使用自动变量； $< 扩展到最左边的先决条件，$@ 扩展到目标。如果您尝试创建 $(build_dir)/foo （无论 $(build_dir) 是什么），Make 会将此规则视为

$(build_dir)/foo: foo
    cp -f foo $(build_dir)/foo

下一个规则，

$(build_dir):
    @if [ ! -x $(build_dir) ]; \
  then \
  mkdir $(build_dir); \
  fi

适用于 $ (build_dir) 本身，并且不必要地复杂。它说“如果 $(build_dir) 不存在，则 mkdir 它”，可以这样写：

$(build_dir):
    mkdir $@

看起来您的主要目标是 $(xpi_file)：

$(xpi_file): $(build_dir) $(xpi_built)

因此，Make 将首先创建 $(build_dir) （如果需要），然后创建列表的成员 %(xpi_built)，其中包括形式$(build_dir)/%。一旦完成这些，它将执行此规则的命令：它将 cd 到 $(build_dir) ，压缩一些内容，并回显一些消息。

$(build_dir)/%: %
    cp -f lt; $@

This is a static pattern rule which uses automatic variables in its command; $< expands to the leftmost prerequisite, $@ expands to the target. If you try to make $(build_dir)/foo (whatever $(build_dir) is), Make will treat this rule as

$(build_dir)/foo: foo
    cp -f foo $(build_dir)/foo

The next rule,

$(build_dir):
    @if [ ! -x $(build_dir) ]; \
  then \
  mkdir $(build_dir); \
  fi

is for $(build_dir) itself, and is unnecessarily complicated. It says "if $(build_dir) doesn't exist, then mkdir it", and it could be written this way:

$(build_dir):
    mkdir $@

It looks as if your primary target is $(xpi_file):

$(xpi_file): $(build_dir) $(xpi_built)

So Make will first make $(build_dir) (if necessary), then the members of the list %(xpi_built), which includes a couple of things of the form $(build_dir)/%. Once those are done, it will execute the commands of this rule: it will cd into $(build_dir), zip some things up, and echo a couple of messages.