将全局 $stdout 重新分配给控制台 - ruby

我试图将 $stdout 设置为临时写入文件，然后再写入文件。

test.rb :
   old_stdout = $stdout    
    $stdout.reopen("mytestfile.out",'w+')
       puts "this goes in mytestfile"
    $stdout= old_stdout
puts "this should be on the console"
    $stdout.reopen("mytestfile1.out",'w+')
       puts "this goes in mytestfile1:"
    $stdout = old_stdout
 puts "this should be back on the console"

这是输出。

ruby test.rb => no output on the console
cat mytestfile.out 
  this goes in mytestfile
  this should be on the console
cat  mytestfile1.out
  this goes in mytestfile1:
  this should be back on the console

我不确定为什么 $stdout 没有重置为控制台？

这个问题可以通过调用来解决dup http://ruby-doc.org/core-1.9.3/Object.html#method-i-dup on $stdout更改之前：

old_stdout = $stdout.dup  
$stdout.reopen("mytestfile.out",'w+')
puts "this goes in mytestfile"
$stdout = old_stdout.dup
puts "this should be on the console"
$stdout.reopen("mytestfile1.out",'w+')
puts "this goes in mytestfile1:"
$stdout = old_stdout
puts "this should be back on the console"

Output:

ruby test.rb
# => this should be on the console
# => this should be back on the console
cat mytestfile.out
# => this goes in mytestfile
cat mytestfile1.out
# => this goes in mytestfile1

以下是我通常将此功能打包到函数中的方式：

# Runs a block of code while blocking stdout.
# Note that /dev/null should be changed to NUL on Windows.
def silence_stdout(log = '/dev/null')
  old = $stdout.dup
  $stdout.reopen(File.new(log, 'w'))
  yield
  $stdout = old
end

Usage:

silence_stdout 'mytestfile.out' do
  puts "this goes in mytestfile"
end

puts "this should be on the console"

silence_stdout 'mytestfile1.out' do
  puts "this goes in mytestfile1"
end

puts "this should be back on the console"

编辑：正如另一张海报提到的，仅在使用纯 Ruby 代码时才需要使用重新打开。上面的函数既适用于纯 Ruby 代码，也适用于使用写入 STDOUT 的 C 扩展等。