Using Powershell to copy and replace content from one file to another

Question

I have two files: FileA and FileB, they are nearly identical.

Both files have a section which starts with ////////// MAIN \\\\\\\\\\. I need to replace the whole content from this point until the end of the file.

So the process high level looks like:

1. find content (starting with ////////// MAIN \\\\\\\\\\) until the end of the file in FileA and copy it to clipboard
2. find content (starting with ////////// MAIN \\\\\\\\\\) until the end of the file in FileB and replace it with the content from the clipboard

How do I do this?

I understand that it would look like this (found it online) but I'm missing the pattern and logic I can use for selecting the text until the end of the file:

# FileA
$inputFileA = "C:\fileA.txt"
# Text to be inserted
$inputFileB = "C:\fileB.txt"
# Output file
$outputFile = "C:\fileC.txt"
# Find where the last </location> tag is
if ((Select-String -Pattern "\</location\>" -Path $inputFileA |
    select -last 1) -match ":(\d+):")
{
    $insertPoint = $Matches[1]
    # Build up the output from the various parts
    Get-Content -Path $inputFileA | select -First $insertPoint | Out-File $outputFile
    Get-Content -Path $inputFileB | Out-File $outputFile -Append
    Get-Content -Path $inputFileA | select -Skip $insertPoint | Out-File $outputFile -Append
}