[System.IO.FileInfo] $file = Get-Item -Path $FilePath 
    $sequenceBOM = New-Object System.Byte[] 3 
    $reader = $file.OpenRead() 
    $bytesRead = $reader.Read($sequenceBOM, 0, 3) 
    $reader.Dispose() 
    #A UTF-8+BOM string will start with the three following bytes. Hex: 0xEF0xBB0xBF, Decimal: 239 187 191 
    if ($bytesRead -eq 3 -and $sequenceBOM[0] -eq 239 -and $sequenceBOM[1] -eq 187 -and $sequenceBOM[2] -eq 191) 
    { 
        $utf8NoBomEncoding = New-Object System.Text.UTF8Encoding($False) 
        [System.IO.File]::WriteAllLines($FilePath, (Get-Content $FilePath), $utf8NoBomEncoding) 
        Write-Host "Remove UTF-8 BOM successfully" 
    } 
    Else 
    { 
        Write-Warning "Not UTF-8 BOM file" 
    }  

如何使用PowerShell从文件中删除UTF8字节顺序标记(BOM)

重要!:这只适用于当一个额外的空格或换行符在开始是没有问题的文件用例 (例如，如果是SQL文件、Java文件或人类可读的文本文件)

可以结合使用创建一个空(非utf8或ASCII (utf8兼容))文件并追加它(如果源文件是一个文件，则将$str替换为gc $src):

" "    |  out-file  -encoding ASCII  -noNewline  $dest
$str  |  out-file  -encoding UTF8   -append     $dest

当一行程序

根据你的用例替换$dest和$str:

$_ofdst = $dest ; " " | out-file -encoding ASCII -noNewline $_ofdst ; $src | out-file -encoding UTF8 -append $_ofdst

作为简单函数

function Out-File-UTF8-noBOM { param( $str, $dest )
  " "    |  out-file  -encoding ASCII  -noNewline  $dest
  $str  |  out-file  -encoding UTF8   -append     $dest
}

与源文件一起使用:

Out-File-UTF8-noBOM  (gc $src),  $dest

与字符串一起使用:

Out-File-UTF8-noBOM  $str,  $dest

可选:继续追加Out-File: "more foo bar" | Out-File -encoding UTF8 -append $dest

我使用的一种技术是使用Out-File cmdlet将输出重定向到ASCII文件。

例如，我经常运行创建另一个SQL脚本并在Oracle中执行的SQL脚本。使用简单的重定向(“>”)，输出将是SQLPlus无法识别的UTF-16格式。要解决这个问题:

sqlplus -s / as sysdba "@create_sql_script.sql" |
Out-File -FilePath new_script.sql -Encoding ASCII -Force

生成的脚本可以通过另一个SQLPlus会话执行，而无需担心Unicode:

sqlplus / as sysdba "@new_script.sql" |
tee new_script.log

更新:正如其他人指出的那样，这会删除非ascii字符。由于用户要求一种“强制”转换的方法，我假设他们并不关心这一点，因为他们的数据可能不包含这样的数据。

如果您关心非ascii字符的保存，这不是适合您的答案。

当使用Set-Content而不是Out-File时，可以指定encoding Byte，它可用于将字节数组写入文件。这与不发出BOM的自定义UTF8编码相结合，给出了所需的结果:

# This variable can be reused
$utf8 = New-Object System.Text.UTF8Encoding $false

$MyFile = Get-Content $MyPath -Raw
Set-Content -Value $utf8.GetBytes($MyFile) -Encoding Byte -Path $MyPath

与使用[IO.File]::WriteAllLines()或类似方法的区别在于，它应该适用于任何类型的项和路径，而不仅仅是实际的文件路径。

    [System.IO.FileInfo] $file = Get-Item -Path $FilePath 
    $sequenceBOM = New-Object System.Byte[] 3 
    $reader = $file.OpenRead() 
    $bytesRead = $reader.Read($sequenceBOM, 0, 3) 
    $reader.Dispose() 
    #A UTF-8+BOM string will start with the three following bytes. Hex: 0xEF0xBB0xBF, Decimal: 239 187 191 
    if ($bytesRead -eq 3 -and $sequenceBOM[0] -eq 239 -and $sequenceBOM[1] -eq 187 -and $sequenceBOM[2] -eq 191) 
    { 
        $utf8NoBomEncoding = New-Object System.Text.UTF8Encoding($False) 
        [System.IO.File]::WriteAllLines($FilePath, (Get-Content $FilePath), $utf8NoBomEncoding) 
        Write-Host "Remove UTF-8 BOM successfully" 
    } 
    Else 
    { 
        Write-Warning "Not UTF-8 BOM file" 
    }  

如何使用PowerShell从文件中删除UTF8字节顺序标记(BOM)

注意:这个答案适用于Windows PowerShell;相比之下，在跨平台的PowerShell核心版(v6+)中，在所有cmdlet中，不含BOM的UTF-8是默认编码。

换句话说:如果您使用PowerShell [Core]版本6或更高版本，默认情况下您将获得无bom的UTF-8文件(您也可以显式地使用-Encoding utf8 / -Encoding utf8NoBOM请求，而使用-utf8BOM获得- bom编码)。 如果你正在运行Windows 10，并且你愿意在系统范围内切换到无bom的UTF-8编码——这可能会有副作用——甚至Windows PowerShell也可以一直使用无bom的UTF-8编码——请看这个答案。

为了补充M. Dudley自己简单而务实的回答(以及ForNeVeR更简洁的重新表述):

A simple, (non-streaming) PowerShell-native alternative is to use New-Item, which (curiously) creates BOM-less UTF-8 files by default even in Windows PowerShell: # Note the use of -Raw to read the file as a whole. # Unlike with Set-Content / Out-File *no* trailing newline is appended. $null = New-Item -Force $MyPath -Value (Get-Content -Raw $MyPath) Note: To save the output from arbitrary commands in the same format as Out-File would, pipe to Out-String first; e.g.: $null = New-Item -Force Out.txt -Value (Get-ChildItem | Out-String) For convenience, below is advanced function Out-FileUtf8NoBom, a pipeline-based alternative that mimics Out-File, which means: you can use it just like Out-File in a pipeline. input objects that aren't strings are formatted as they would be if you sent them to the console, just like with Out-File. an additional -UseLF switch allows you use Unix-format LF-only newlines ("`n") instead of the Windows-format CRLF newlines ("`r`n") you normally get.

例子:

(Get-Content $MyPath) | Out-FileUtf8NoBom $MyPath # Add -UseLF for Unix newlines

注意(Get-Content $MyPath)是如何包含在(…)中，这确保在通过管道发送结果之前打开、完整读取和关闭整个文件。为了能够写回相同的文件(在适当的位置更新它)，这是必要的。 一般来说，这种技术是不可取的，原因有二:(a)整个文件必须适合内存;(b)如果命令被中断，数据将丢失。

内存使用注意事项:

达德利先生自己的回答 和上面的New-Item替代方案要求首先在内存中构建整个文件内容，这对于大的输入集可能是个问题。 下面的函数不需要这样做，因为它是作为一个代理(包装器)函数实现的(关于如何定义这样的函数的简明摘要，请参阅这个答案)。

Out-FileUtf8NoBom函数源代码:

注意:该功能也可以作为麻省理工学院授权的Gist使用，并且今后只会维护它。

你可以直接使用以下命令安装它(虽然我个人可以向你保证这样做是安全的，但在直接执行脚本之前，你应该总是检查脚本的内容):

# Download and define the function.
irm https://gist.github.com/mklement0/8689b9b5123a9ba11df7214f82a673be/raw/Out-FileUtf8NoBom.ps1 | iex

function Out-FileUtf8NoBom {

  <#
  .SYNOPSIS
    Outputs to a UTF-8-encoded file *without a BOM* (byte-order mark).

  .DESCRIPTION

    Mimics the most important aspects of Out-File:
      * Input objects are sent to Out-String first.
      * -Append allows you to append to an existing file, -NoClobber prevents
        overwriting of an existing file.
      * -Width allows you to specify the line width for the text representations
        of input objects that aren't strings.
    However, it is not a complete implementation of all Out-File parameters:
      * Only a literal output path is supported, and only as a parameter.
      * -Force is not supported.
      * Conversely, an extra -UseLF switch is supported for using LF-only newlines.

  .NOTES
    The raison d'être for this advanced function is that Windows PowerShell
    lacks the ability to write UTF-8 files without a BOM: using -Encoding UTF8 
    invariably prepends a BOM.

    Copyright (c) 2017, 2022 Michael Klement <mklement0@gmail.com> (http://same2u.net), 
    released under the [MIT license](https://spdx.org/licenses/MIT#licenseText).

  #>

  [CmdletBinding(PositionalBinding=$false)]
  param(
    [Parameter(Mandatory, Position = 0)] [string] $LiteralPath,
    [switch] $Append,
    [switch] $NoClobber,
    [AllowNull()] [int] $Width,
    [switch] $UseLF,
    [Parameter(ValueFromPipeline)] $InputObject
  )

  begin {

    # Convert the input path to a full one, since .NET's working dir. usually
    # differs from PowerShell's.
    $dir = Split-Path -LiteralPath $LiteralPath
    if ($dir) { $dir = Convert-Path -ErrorAction Stop -LiteralPath $dir } else { $dir = $pwd.ProviderPath }
    $LiteralPath = [IO.Path]::Combine($dir, [IO.Path]::GetFileName($LiteralPath))
    
    # If -NoClobber was specified, throw an exception if the target file already
    # exists.
    if ($NoClobber -and (Test-Path $LiteralPath)) {
      Throw [IO.IOException] "The file '$LiteralPath' already exists."
    }
    
    # Create a StreamWriter object.
    # Note that we take advantage of the fact that the StreamWriter class by default:
    # - uses UTF-8 encoding
    # - without a BOM.
    $sw = New-Object System.IO.StreamWriter $LiteralPath, $Append
    
    $htOutStringArgs = @{}
    if ($Width) { $htOutStringArgs += @{ Width = $Width } }

    try { 
      # Create the script block with the command to use in the steppable pipeline.
      $scriptCmd = { 
        & Microsoft.PowerShell.Utility\Out-String -Stream @htOutStringArgs | 
          . { process { if ($UseLF) { $sw.Write(($_ + "`n")) } else { $sw.WriteLine($_) } } }
      }  
      
      $steppablePipeline = $scriptCmd.GetSteppablePipeline($myInvocation.CommandOrigin)
      $steppablePipeline.Begin($PSCmdlet)
    }
    catch { throw }

  }

  process
  {
    $steppablePipeline.Process($_)
  }

  end {
    $steppablePipeline.End()
    $sw.Dispose()
  }

}