我试图理解一个执行 Javac 并向其传递一些简单参数的简单命令行字符串。完整的命令行是：
javac -d $(OUTPATH) -sourcepath $(SOURCEPATH) $<
除了最后的标记：$< 之外，这一行中的所有内容对我来说都是简单易懂的。
这些标记是什么意思？
附录：确实，评论者是正确的。该行出现在 makefile 中。现在对我来说很明显，但当我写这个问题时，makefile 被传递给 make 并且不是 shell 脚本。
请注意： $ 做什么？和 $@ 代表 Makefile？ 也讨论了这一点（当我查找以前的问题时没有看到它）。
I am trying to understand a simple command-line string that executes Javac and passes it some simple arguments. The complete command line is:
javac -d $(OUTPATH) -sourcepath $(SOURCEPATH) lt;
Everything in this line is straightforward and understandable to me except for the final tokens: $<.
What do these tokens mean?
ADDENDUM: Indeed, the commenters are correct. This line occurs within a makefile. It is obvious to me now, but not when I wrote this question, that a makefile is passed to make and is not a shell script.
Please note: What do $< and $@ represent in a Makefile? also discusses this (I did not see it when I looked for previous questions about this).
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这看起来像是 makefile 中的内容，而不是命令行中的内容。在这种情况下，
$<扩展为当前目标的第一个先决条件。即.class目标所依赖的.java文件。This looks like something from a makefile, not a command line. In that case,
$<expands to the first prerequisite of the current target. That is, the.javafile that the.classtarget depends on.