PowerShell out-file: prevent encoding changes

Out-File has a default encoding unless overriden with the -Encoding parameter:

What I've done to solve this is to try to get the original file's encoding by reading trying to read it's byte order mark and using it as the-Encoding parameter value.

Here's an example processing a bunch of text file paths, getting the original encoding, processing the content and writing it back to file with the original's encoding.

function Get-FileEncoding {    param ( [string] $FilePath )    [byte[]] $byte = get-content -Encoding byte -ReadCount 4 -TotalCount 4 -Path $FilePath    if ( $byte[0] -eq 0xef -and $byte[1] -eq 0xbb -and $byte[2] -eq 0xbf )        { $encoding = 'UTF8' }      elseif ($byte[0] -eq 0xfe -and $byte[1] -eq 0xff)        { $encoding = 'BigEndianUnicode' }    elseif ($byte[0] -eq 0xff -and $byte[1] -eq 0xfe)         { $encoding = 'Unicode' }    elseif ($byte[0] -eq 0 -and $byte[1] -eq 0 -and $byte[2] -eq 0xfe -and $byte[3] -eq 0xff)        { $encoding = 'UTF32' }    elseif ($byte[0] -eq 0x2b -and $byte[1] -eq 0x2f -and $byte[2] -eq 0x76)        { $encoding = 'UTF7'}    else        { $encoding = 'ASCII' }    return $encoding}foreach ($textFile in $textFiles) {    $encoding = Get-FileEncoding $textFile    $content = Get-Content -Encoding $encoding    # Process content here...    $content | Set-Content -Path $textFile -Encoding $encoding}

Update Here is an example of getting the original file encoding using the StreamReader class. The example reads the first 3 bytes of the file so that the CurrentEncoding property gets set based on the result of its internal BOM detection routine.

http://msdn.microsoft.com/en-us/library/9y86s1a9.aspx

The detectEncodingFromByteOrderMarks parameter detects the encoding by looking at the first three bytes of the stream. It automatically recognizes UTF-8, little-endian Unicode, and big-endian Unicode text if the file starts with the appropriate byte order marks. Otherwise, the UTF8Encoding is used. See the Encoding.GetPreamble method for more information.

http://msdn.microsoft.com/en-us/library/system.text.encoding.getpreamble.aspx

$text = @" This ismy text filecontents."@#Create text file.[IO.File]::WriteAllText($filePath, $text, [System.Text.Encoding]::BigEndianUnicode)#Create a stream reader to get the file's encoding and contents.$sr = New-Object System.IO.StreamReader($filePath, $true)[char[]] $buffer = new-object char[] 3$sr.Read($buffer, 0, 3)  $encoding = $sr.CurrentEncoding$sr.Close()#Show the detected encoding.$encoding#Update the file contents.$content = [IO.File]::ReadAllText($filePath, $encoding)$content2 = $content -replace "my" , "your"#Save the updated contents to file.[IO.File]::WriteAllText($filePath, $content2, $encoding)#Display the result.Get-Content $filePath