OutOfMemoryException when running my PowerShell script - powershell

Question

Here's the PowerShell script I am using to add "segment99" to the beginning of all the text files (one by one) within a folder:
Set Environmental Variables:
$PathData = '<<ESB_Data_Share_HSH>>\RwdPnP'
Go to each text file in the specified folder and add header to the file:
Get-ChildItem $PathData -filter 'test_export.txt'|%{
$content = '"segment99" ' + [io.file]::ReadAllText($_.FullName)
[io.file]::WriteAllText(($_.FullName -replace '\.txt$','_99.txt'),$content)
}
This is giving me the following error:
Error: Exception calling "ReadAllText" with "1" argument(s): "Exception of type 'Syste
Error: m.OutOfMemoryException' was thrown."
Error: At D:\apps\MVPSI\JAMS\Agent\Temp\JAMSTemp13142.ps1:17 char:51
Error: + $content = '"segment99" ' + [io.file]::ReadAllText <<<< ($_.FullName)
Error: + CategoryInfo : NotSpecified: (:) [], MethodInvocationException
Error: + FullyQualifiedErrorId : DotNetMethodException
Error:
I am running this code on a folder that has 20 files, each over 2 GB.
How can I fix this?

Answer 1

Copying a header file + a large file to a new file will be less prone to outofmemory exceptions (for files of that size):
$header = '"segment99"'
$header | out-file header.txt -encoding ASCII
$pathdata = "."
Get-ChildItem $PathData -filter 'test_export.txt' | %{
$newName = "{0}{1}{2}" -f $_.basename,"_99",$_.extension
$newPath = join-path (split-path $_.fullname) $newname
cmd /c copy /b "header.txt"+"$($_.fullname)" "$newpath"
}

Answer 2

This is not optimal code but it solves the task without reading all text to memory: it adds the header to the first line and then outputs other lines. Also, note that it does nothing if the input file is empty.
Get-ChildItem $PathData -Filter 'test_export.txt' | %{
$header = $true
Get-Content $_.FullName | .{process{
if ($header) {
'"segment99" ' + $_
$header = $false
}
else {
$_
}
}} | Set-Content ($_.FullName -replace '\.txt$', '_99.txt')
}