PowerShell out-file: prevent encoding changes

Question

I'm currently working on some search and replace operation that I'm trying to automate using powershell. Unfortunately I recognized yesterday that we've different file encodings in our codebase (UTF8 and ASCII). Because we're doing these search and replace operations in a different branch I can't change the file encodings at this stage.

If I'm running the following lines it changes all files to UCS-2 Little Eindian even though my default powershell encoding is set to iso-8859-1 (Western European (Windows)).

$content = Get-Content $_.Path
$content -replace 'myOldText' , 'myNewText' | Out-File $_.Path

Is there a way to prevent powershell from changing the file's encoding?

Answer 1

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 is
my text file
contents.
"@

#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