Change and save .nc files - powershell

Question

I have a massive amount of .nc files (text files) where I need to change different lines based on their linenumer and content.
Example:
So far I have:
Get-ChildItem I:\temp *.nc -recurse | ForEach-Object {
$c = ($_ | Get-Content)
$c = $c -replace "S355J2","S235JR2"
$c = $c.GetType() | Format-Table -AutoSize
$c = $c -replace $c[3],$c[4]
[IO.File]::WriteAllText($_.FullName, ($c -join "`r`n"))
}
This is not working, however, since it returns only a few PowerShell lines to each file, instead of the original (changed) content.

Answer 1

I don't know what you expect $c = $c.GetType() | Format-Table -AutoSize to do, but it most likely doesn't do whatever it is you're expecting.
If I understand your question correctly you essentially want to
remove the line pos,
replace the code S355J2 with S235JR2, and
remove a section SI if it exists.
The following code should work:
Get-ChildItem I:\temp *.nc -Recurse | ForEach-Object {
(Get-Content $_.FullName | Out-String) -replace 'pos\r\n\s+' -replace 'S355J2', 'S235JR2' -replace '(?m)^SI\r\n(\s+.*\n)+' |
Set-Content $_.FullName
}
Out-String mangles the content of the input file into a single string, and the daisy-chained replacement operations modify that string before it's written back to the file. The expression (?m)^SI\r\n(\s+.*\n)+ matches a line beginning with SI and followed by one or more indented lines. The (?m) modifier is to allow matching start-of-line in a multiline string, otherwise ^ would only match the beginning of the string.
Edit: If you need to replace variable text in the 3rd line with the text from the 4th line (thus duplicating the 4th line) you're indeed better off working with an array for that. Delay the mangling of the string array until after that replacement:
Get-ChildItem I:\temp *.nc -Recurse | ForEach-Object {
$txt = #(Get-Content $_.FullName)
$txt[3] = $txt[4]
($txt | Out-String) -replace 'S355J2', 'S235JR2' -replace '(?m)^SI\r\n(\s+.*\n)+' |
Set-Content $_.FullName
}