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如何在 Ruby 中临时重定向 stderr？

发布于 2024-10-08 09:07:05 字数 92 浏览 4 评论 0原文

我想在一个块的持续时间内临时重定向 Ruby 脚本中的 stderr，确保在块结束时将其重置为其原始值。

我在 ruby 文档中找不到如何做到这一点。

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樱花坊 2024-10-15 09:07:05

在 Ruby 中，$stderr 指的是当前使用作为 stderr 的输出流，而 STDERR 是默认标准错误流。可以很容易地临时将不同的输出流分配给$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：

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。

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

Now you can do the following:

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

captured_output
#=> "test\n"

The same principle also works for $stdout and STDOUT.

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〆一缕阳光ご 2024-10-15 09:07:05

这是一个更抽象的解决方案（归功于 David Heinemeier Hansson）：

def silence_streams(*streams)
  on_hold = streams.collect { |stream| stream.dup }
  streams.each do |stream|
    stream.reopen(RUBY_PLATFORM =~ /mswin/ ? 'NUL:' : '/dev/null')
    stream.sync = true
  end
  yield
ensure
  streams.each_with_index do |stream, i|
    stream.reopen(on_hold[i])
  end
end

用法：

silence_streams(STDERR) { do_something }

Here is a more abstract solution (credit goes to David Heinemeier Hansson):

def silence_streams(*streams)
  on_hold = streams.collect { |stream| stream.dup }
  streams.each do |stream|
    stream.reopen(RUBY_PLATFORM =~ /mswin/ ? 'NUL:' : '/dev/null')
    stream.sync = true
  end
  yield
ensure
  streams.each_with_index do |stream, i|
    stream.reopen(on_hold[i])
  end
end

Usage:

silence_streams(STDERR) { do_something }

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等风也等你 2024-10-15 09:07:05

本质上与 @molf 的答案相同，并且具有相同的用法：

require "stringio"
def capture_stderr
  real_stderr, $stderr = $stderr, StringIO.new
  yield
  $stderr.string
ensure
  $stderr = real_stderr
end

它使用 StringIO 更加简洁，并将 $stderr 保留为调用 capture_stderr 之前的内容。

Essentially the same as @molf's answer, and has the same usage:

require "stringio"
def capture_stderr
  real_stderr, $stderr = $stderr, StringIO.new
  yield
  $stderr.string
ensure
  $stderr = real_stderr
end

It uses StringIO very slightly more concisely, and preserves $stderr as whatever it was before capture_stderr was called.

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献世佛 2024-10-15 09:07:05

我喜欢 StringIO 的答案。但是，如果您正在调用外部进程，并且 $stderr = StringIO.new 不起作用，您可能会将 stderr 写入临时文件：

require 'tempfile'

def capture_stderr
  backup_stderr = STDERR.dup
  begin
    Tempfile.open("captured_stderr") do |f|
      STDERR.reopen(f)
      yield
      f.rewind
      f.read
    end
  ensure
    STDERR.reopen backup_stderr
  end
end

I like the StringIO answers. But if you are calling an external process, and $stderr = StringIO.new doesn't work, you might write stderr out to a temporary file:

require 'tempfile'

def capture_stderr
  backup_stderr = STDERR.dup
  begin
    Tempfile.open("captured_stderr") do |f|
      STDERR.reopen(f)
      yield
      f.rewind
      f.read
    end
  ensure
    STDERR.reopen backup_stderr
  end
end

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