Unable to Find and Replace a string in 2GB XML file using Powershell

The typical method is to use .Net methods to do it line by line.

Assuming you've got sensible line breaks, you can do something like this:

$FilePath = '...';
$NewFilePath = '...';

$Reader = New-Object -TypeName System.IO.StreamReader -ArgumentList $FilePath;
$Writer = New-Object -TypeName System.IO.StreamWriter -ArgumentList $NewFilePath;

while (($Line = $Reader.ReadLine()) -ne $null) {
    $Writer.WriteLine($Line.Replace('.000000000Z','.732Z'));
}

$Reader.Close();
$Writer.Close();

If your XML file is a single line of text, it gets more complicated.

Get-Content loads the entire file content into RAM to be acted upon.

You need to upgrade your RAM Use a deferent method and there are a few of them.

Get-Content
Get-Content -Raw
Get-Content -ReadCount
Switch -File

The .Net reader is the most optimal

[System.IO.File]::ReadAllText()
[System.IO.File]::ReadAllLines()
[System.IO.File]::ReadLines()
[System.IO.File]::OpenText().readtoend()

System.IO.File.ReadLines() is more than likely your best choice as it returns all the lines of a file, but lets you begin iterating over the lines immediately which means it does not have to store the entire contents in memory. More details here: https://msdn.microsoft.com/en-us/library/dd383503.aspx

Requires .NET 4.0 or higher.
foreach ($line in [System.IO.File]::ReadLines($filename)) {
    # do something with $line
}

So, you could do something like this...

$reader = [System.IO.File]::OpenText("my.log")
try {
    for() {
        $line = $reader.ReadLine()
        if ($line -eq $null) { break }
        # process the line
        $line
    }
}
finally {
    $reader.Close()
}

Or shorten it to this...

$reader = [System.IO.File]::OpenText("my.log")
while($null -ne ($line = $reader.ReadLine())) {
    $line
}