如何在 Ruby 中临时重定向 stderr? [英] How do I temporarily redirect stderr in Ruby?

问题描述

我想在块的持续时间内临时重定向 Ruby 脚本中的 stderr，确保在块的末尾将其重置为原始值.

I'd like to temporarily redirect stderr in a Ruby script for the duration of a block, ensuring that I reset it to its original value at the end of the block.

我在 ruby​​ 文档中找不到如何执行此操作的问题.

I had trouble finding how to do this in the ruby docs.

推荐答案

在 Ruby 中，$stderr 指的是当前使用作为标准错误的输出流，而 STDERR 是默认 stderr 流.很容易将不同的输出流临时分配给 $stderr.

In Ruby, $stderr refers to the output stream that is currently used as stderr, whereas STDERR is the default stderr stream. It is easy to temporarily assign a different output stream to $stderr.

require "stringio"

def capture_stderr
  # The output stream must be an IO-like object. In this case we capture it in
  # an in-memory IO object so we can return the string value. You can assign any
  # IO object here.
  previous_stderr, $stderr = $stderr, StringIO.new
  yield
  $stderr.string
ensure
  # Restore the previous value of stderr (typically equal to STDERR).
  $stderr = previous_stderr
end

现在您可以执行以下操作:

Now you can do the following:

captured_output = capture_stderr do
  # Does not output anything directly.
  $stderr.puts "test"
end

captured_output
#=> "test\n"

同样的原理也适用于 $stdout 和 STDOUT.

The same principle also works for $stdout and STDOUT.

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