Powershell - Read, Alter Line, Write new line over old in Text Document - powershell

Question

I am reading in line by line of a text file. If I see a specific string, I locate the first and last of a specific character, use two substrings to create a smaller string, then replace the line in the text file.
The difficult part: I have the line of text stored in a variable, but cannot figure out how to write this new line over the old line in the text document.
Excuse the crude code - I have been testing things and only started playing with PowerShell a few hours ago.
foreach($line in [System.IO.File]::ReadLines("C:\BatchPractice\test.txt"))
{
Write-Output $line
if ($line.Contains("dsa")) {
Write-Output "TRUEEEEE"
}
$positionF = $line.IndexOf("\")+1
$positionL = $line.LastIndexOf("\")+1
$lengthT = $line.Length
Write-Output ($positionF)
Write-Output $positionL
Write-Output $lengthT
if($line.Contains("\")){
Write-Output "Start"
$combine = $line.Substring(0,$positionF-1) + $line.Substring($postionL,($lengthT-$positionL))
Write-Output $combine
$line1 = $line.Substring(0,$positionF-1)
$line2 = $line.Substring($positionL,($lengthT-$positionL))
$combined = $line1 + $line2
Write-Output $combined
Write-Output "Close"
}
}```

Answer 1

You can save the file as arrays in Get-Content and Set-Content:
$file=(Get-Content "C:\BatchPractice\test.txt")
Then you can edit it like arrays:
$file[LINE_NUMBER]="New line"
Where LINE_NUMBER is the line number starting from 0.
And then overwrite to file:
$file|Set-Content "C:\BatchPractice\test.txt"
You can implement this in code. Create a variable $i=0 and increment it at the end of loop. Here $i will be the line number at each iteration.
HTH

Answer 2

Based on your code it seems you want to take any line that contains 'dsa' and remove the contents after the first backslash up until the last backslash. If that's the case I'd recommend simplifying your code with regex. First I made a sample file since none was provided.
$tempfile = New-TemporaryFile
#'
abc\def\ghi\jkl
abc\dsa\ghi\jkl
zyx\vut\dsa\srq
zyx\vut\srq\pon
'# | Set-Content $tempfile -Encoding UTF8
Now we will read in all lines (unless this is a massive file)
$text = Get-Content $tempfile -Encoding UTF8
Next we'll make a regex object with the pattern we want to replace. The double backslash is to escape the backslash since it has meaning to regex.
$regex = [regex]'(?<=.+\\).+\\'
Now we will loop over every line, if it has dsa in it we will run the replace against it, otherwise we will output the line.
$text | ForEach-Object {
if($_.contains('dsa'))
{
$regex.Replace($_,'')
}
else
{
$_
}
} -OutVariable newtext
You'll see the output on the screen but it's also capture in $newtext variable. I recommend ensuring it is the output you are after prior to writing.
abc\def\ghi\jkl
abc\jkl
zyx\srq
zyx\vut\srq\pon
Once confirmed, simply write it back to the file.
$newtext | Set-Content $tempfile -Encoding UTF8
You can obviously combine the steps as well.
$text | ForEach-Object {
if($_.contains('dsa'))
{
$regex.Replace($_,'')
}
else
{
$_
}
} | Set-Content $tempfile -Encoding UTF8