powershell 中的“>>”有什么作用？

Question

当我运行这个命令时：

Get-Content generated\no_animate.css >> generated\all.css

它将第一个文件的内容复制到第二个文件中。该符号的官方术语是什么>>？我在哪里可以找到有关此符号和其他符号的更多信息？

毫不奇怪，在谷歌中搜索>>并没有提供太多信息。

Answer 1

感谢 EBGreen 我找到了这个信息。

https://technet.microsoft.com/en-us/library/hh847746.aspx

主题 about_Redirection

简短说明 解释如何将输出从 Windows PowerShell 重定向到文本文件。

详细说明 默认情况下，Windows PowerShell 将其命令输出发送到 Windows PowerShell 控制台。但是，您可以将输出定向到文本文件，并且可以将错误输出重定向到常规输出流。

You can use the following methods to redirect output:

    - Use the Out-File cmdlet, which sends command output to a text file. 
      Typically, you use the Out-File cmdlet when you need to use its 
      parameters, such as the Encoding, Force, Width, or NoClobber 
      parameters.

    - Use the Tee-Object cmdlet, which sends command output to a text file 
      and then sends it to the pipeline.

    - Use the Windows PowerShell redirection operators.

WINDOWS POWERSHELL 重定向运算符 重定向运算符使您能够将特定类型的输出发送到文件和成功输出流。

  The Windows PowerShell redirection operators use the following characters 
  to represent each output type:
    *   All output
    1   Success output
    2   Errors
    3   Warning messages
    4   Verbose output
    5   Debug messages

          NOTE: The All (*), Warning (3), Verbose (4) and Debug (5) redirection operators were introduced
                        in Windows PowerShell 3.0. They do not work in earlier versions of Windows PowerShell.

  The Windows PowerShell redirection operators are as follows.
  Operator  Description                Example  
  --------  ----------------------     ------------------------------
  >         Sends output to the        Get-Process > Process.txt
            specified file.

  >>        Appends the output to      dir *.ps1 >> Scripts.txt
            the contents of the  
            specified file.

  2>        Sends errors to the        Get-Process none 2> Errors.txt
            specified file.

  2>>       Appends errors to          Get-Process none 2>> Save-Errors.txt
            the contents of the 
            specified file.

  2>&1      Sends errors (2) and       Get-Process none, Powershell 2>&1
            success output (1) 
            to the success 
            output stream.

  3>        Sends warnings to the      Write-Warning "Test!" 3> Warnings.txt
            specified file.

  3>>       Appends warnings to        Write-Warning "Test!" 3>> Save-Warnings.txt
            the contents of the 
            specified file.

  3>&1      Sends warnings (3) and     function Test-Warning 
            success output (1)         {  Get-Process PowerShell; 
            to the success                Write-Warning "Test!" }
            output stream.             Test-Warning 3>&1

  4>        Sends verbose output to    Import-Module * -Verbose 4> Verbose.txt
            the specified file.

  4>>       Appends verbose output     Import-Module * -Verbose 4>> Save-Verbose.txt
            to the contents of the 
            specified file.

  4>&1      Sends verbose output (4)   Import-Module * -Verbose 4>&1
            and success output (1)    
            to the success output
            stream.              

  5>        Sends debug messages to    Write-Debug "Starting" 5> Debug.txt
            the specified file.

  5>>       Appends debug messages     Write-Debug "Saving" 5>> Save-Debug.txt
            to the contents of the 
            specified file.

  5>&1      Sends debug messages (5)   function Test-Debug 
            and success output (1)     { Get-Process PowerShell 
            to the success output        Write-Debug "PS" }
            stream.                    Test-Debug 5>&1

  *>        Sends all output types     function Test-Output
            to the specified file.     { Get-Process PowerShell, none  
                                         Write-Warning "Test!"
  *>>       Appends all output types     Write-Verbose "Test Verbose"
            to the contents of the       Write-Debug "Test Debug" } 
            specified file.            
                                       Test-Output *> Test-Output.txt
  *>&1      Sends all output types     Test-Output *>> Test-Output.txt
            (*) to the success output  Test-Output *>&1      
            stream.     


The syntax of the redirection operators is as follows:

   <input> <operator> [<path>\]<file>

If the specified file already exists, the redirection operators that do not
append data (> and n>) overwrite the current contents of the file without 
warning. However, if the file is a read-only, hidden, or system file, the 
redirection fails. The append redirection operators (>> and n>>) do not 
write to a read-only file, but they append content to a system or hidden 
file.


To force the redirection of content to a read-only, hidden, or system file,
use the Out-File cmdlet with its Force parameter. When you are writing to 
files, the redirection operators use Unicode encoding. If the file has a 
different encoding, the output might not be formatted correctly. To
redirect content to non-Unicode files, use the Out-File cmdlet with its
Encoding parameter.

另请参见输出文件 Tee 对象 about_Operators about_Command_Syntax about_Path_Syntax