blocks|key|2952582|text|$stdout是代表当前标准输出的全局变量。STDOUT是代表标准输出的常量，通常是$stdout的默认值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|2952583|由于STDOUT是常量，您不应该重新定义它，但是，您可以重新定义$stdout而不会出现错误/警告(重新定义STDOUT将引发警告)。例如，您可以执行以下操作：|2952584|$stdout+=+STDERR|code-block|syntax|javascript|2952585|$stderr和STDERR也是如此|2952586|2952587|因此，要回答问题的另一部分，请使用全局变量来重定向输出，而不是常量。只需小心在代码中进一步更改它，重新定义全局变量可能会影响应用程序的其他部分。|2952588|entityMap^0|0|7|M|6|16|7|H|4|10|2|0|2|6|W|7|1I|6|0|0|0|7|8|6|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|D]|$9|13|A|14|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|E|@]|F|$]]|$1|I|3|J|5|K|7|1C|8|@]|E|@]|F|$L|M]]|$1|N|3|O|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|E|@]|F|$]]|$1|P|3|-4|5|6|7|1I|8|@]|E|@]|F|$]]|$1|Q|3|R|5|6|7|1J|8|@]|E|@]|F|$]]|$1|S|3|-4|5|6|7|1K|8|@]|E|@]|F|$]]]|T|$]]

<code>$stdout</code> is a global variable that represents the current standard output. <code>STDOUT</code> is a constant representing standard output and is typically the default value of <code>$stdout</code>.

With <code>STDOUT</code> being a constant, you shouldn't re-define it, however, you can re-define <code>$stdout</code> without errors/warnings (re-defining <code>STDOUT</code> will raise a warning). for example, you can do:

<pre><code>$stdout = STDERR
</code></pre>

Same goes for <code>$stderr</code> and <code>STDERR</code>

<hr>

So, to answer the other part of your question, use the global variables to redirect output, not the constants. Just be careful to change it back further on in your code, re-defining global variables can impact other parts of your application.

blocks|key|3166381|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3166382|STDOUT是全局常量，因此不应更改。|unordered-list-item|offset|length|style|CODE|3166383|$stdout是预定义变量，因此可以更改。|3166384|3166385|如果您使用shell进行重定向：|3166386|$+ruby+test.rb+>+test.log|code-block|syntax|javascript|3166387|然后，在脚本执行之前确定使用哪个文件描述符作为脚本的文件描述符都无关紧要。|3166388|但是，如果您试图从Ruby脚本中更改OS的STDOUT的文件描述符，例如根据一周中的当前日期将输出发送到一组循环的日志文件，那么您将需要确保使用$stdout。|3166389|entityMap^0|0|0|6|0|0|7|0|0|0|0|0|20|7|0^^$0|@$1|2|3|-4|4|5|6|X|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|Y|7|@$D|Z|E|10|F|G]]|8|@]|9|$]]|$1|H|3|I|4|C|6|11|7|@$D|12|E|13|F|G]]|8|@]|9|$]]|$1|J|3|-4|4|5|6|14|7|@]|8|@]|9|$]]|$1|K|3|L|4|5|6|15|7|@]|8|@]|9|$]]|$1|M|3|N|4|O|6|16|7|@]|8|@]|9|$P|Q]]|$1|R|3|S|4|5|6|17|7|@]|8|@]|9|$]]|$1|T|3|U|4|5|6|18|7|@$D|19|E|1A|F|G]]|8|@]|9|$]]|$1|V|3|-4|4|5|6|1B|7|@]|8|@]|9|$]]]|W|$]]

<ul>
<li><code>STDOUT</code> is a global constant, so it should not be changed. </li>
<li><code>$stdout</code> is a predefined variable, so it can be changed.</li>
</ul>

If you are using the shell to do redirection:

<pre><code>$ ruby test.rb &gt; test.log
</code></pre>

then it doesn't matter which one you use as the file descriptor for your script is being determined before your script is executed.

However, if you are trying to change the file descriptor for the OS's STDOUT from within your Ruby script, for example to send output to a rotating set of log files based on the current day of the week, then you'll want to make sure you use <code>$stdout</code>.

blocks|key|263377|text|$stdout和STDOUT都有不同的含义。Ruby's+documentation在这个话题上说得很清楚：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|263378|263379|blockquote|263380|263381|263382|$stdout+-当前标准output.|unordered-list-item|263383|STDOUT+-标准输出。$stdout的默认值。|263384|263385|当您想要写入标准输出时，实际上是指当前的标准输出，因此您应该写入$stdout。|263386|STDOUT也不是一无是处。它存储$stdout的默认值。如果您重新分配了$stdout，则可以使用$stdout+=+STDOUT将其恢复为以前的值。|263387|此外，还有一个预定义的变量：|263388|263389|263390|263391|printf+-打印的默认输出，|263392|$>，默认情况下为$stdout。|263393|263394|然而，在Ruby2.3中，它看起来只是作为$stdout的一个别名。重新分配$stdout会更改$>的值，反之亦然。|263395|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-2.3.0/doc/globals_rdoc.html^0|0|7|8|6|M|K|0|0|0|0|0|0|0|7|0|0|6|0|0|W|7|0|0|6|H|7|11|7|1E|G|0|0|0|0|0|0|0|2|9|7|0|0|L|7|12|7|1C|2|0^^$0|@$1|2|3|4|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@$9|1J|A|1K|1|1L]]|E|$]]|$1|F|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]|$1|G|3|-4|5|H|7|1N|8|@]|D|@]|E|$]]|$1|I|3|-4|5|6|7|1O|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]|$1|K|3|L|5|M|7|1Q|8|@$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|N|3|O|5|M|7|1T|8|@$9|1U|A|1V|B|C]]|D|@]|E|$]]|$1|P|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|20|8|@$9|21|A|22|B|C]|$9|23|A|24|B|C]|$9|25|A|26|B|C]|$9|27|A|28|B|C]]|D|@]|E|$]]|$1|U|3|V|5|6|7|29|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|2A|8|@]|D|@]|E|$]]|$1|X|3|-4|5|H|7|2B|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|2C|8|@]|D|@]|E|$]]|$1|Z|3|10|5|6|7|2D|8|@]|D|@]|E|$]]|$1|11|3|12|5|M|7|2E|8|@$9|2F|A|2G|B|C]|$9|2H|A|2I|B|C]]|D|@]|E|$]]|$1|13|3|-4|5|6|7|2J|8|@]|D|@]|E|$]]|$1|14|3|15|5|6|7|2K|8|@$9|2L|A|2M|B|C]|$9|2N|A|2O|B|C]|$9|2P|A|2Q|B|C]]|D|@]|E|$]]|$1|16|3|-4|5|6|7|2R|8|@]|D|@]|E|$]]]|17|$18|$5|19|1A|1B|E|$1C|1D]]]]

Both <code>$stdout</code> and <code>STDOUT</code> have different meanings. <a href="http://ruby-doc.org/core-2.3.0/doc/globals_rdoc.html" rel="noreferrer">Ruby's documentation</a> is pretty clear on this topic:

<blockquote>
 <ul>
 <li><code>$stdout</code> – The current standard output.</li>
 <li><code>STDOUT</code> – The standard output. The default value for $stdout.</li>
 </ul>
</blockquote>

When you want to write to the standard output, then you actually mean the current standard output, thus you should write to <code>$stdout</code>.

<code>STDOUT</code> isn't useless too. It stores the default value for <code>$stdout</code>. If you ever reassign <code>$stdout</code>, then you can restore it to the previous value with <code>$stdout = STDOUT</code>.

Furthermore, there's one more predefined variable:

<blockquote>
 <ul>
 <li><code>$&gt;</code> – The default output for print, printf, which is <code>$stdout</code> by default.</li>
 </ul>
</blockquote>

However it looks like in Ruby 2.3 it simply behaves as an alias for <code>$stdout</code>. Reassigning <code>$stdout</code> changes the value of <code>$&gt;</code> and vice versa.

In Ruby, what is the difference between <code>$stdout</code> (preceded by a dollar sign) and <code>STDOUT</code> (in all caps)? When doing output redirection, which should be used and why? The same goes for <code>$stderr</code> and <code>STDERR</code>.

Edit: Just found a <a href="https://stackoverflow.com/questions/4279604/what-is-the-difference-between-stdin-and-stdin-in-ruby">related question</a>.

Difference between $stdout and STDOUT in Ruby

日志文件

Ruby语言

在Ruby语言中，$stdout (前面有一个美元符号)和STDOUT (全部大写)有什么区别？当做输出重定向时，应该使用哪一个?为什么？$stderr和STDERR也是如此。编辑：刚刚找到了一个。

问$stdout和STDOUT在Ruby语言中的区别
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