Removing multiple strings within a text file using powershell

Question

Alright I am still really new to PowerShell and i've sifted through a few different threads on here trying to find the best way to go about this. This is the closest I could find to how I need to modify the file. If their is any better ways to go about this I am all ears, like I said still pretty new to powershell.

Goal

• I want to delete the entire group within a text file, then write it to the same file (if possible)

Issue

1. I want to delete lines 1 through random number.
2. The very first line is always the same within the group, and is always on the same line number.
3. The very last line of the group is always the same, but it is never on the same line number.
4. I've got the desired output I want, but I am running into issues writing it back to the same file.
5. I've tried -replace and set-content but I run into errors at this portion.

Example of the text files within the folder.

I want this deleted
here
here
here 
here
To here 

but i want this kept in file 1

File 2

I want this deleted
here
here
here 
here
here
here
To here 

but i want this kept in file 2

Below is what I have come up with.

$files = Get-ChildItem 
Foreach-Object {

    #Targeting the specific file
    $keep = $true
    Get-Content $files | Where-Object { 
      if ( $_.StartsWith("I want this deleted")) {
        $keep = $false
      } elseif ( -not $keep -and $_.StartsWith("but") ) {
        $keep = $true
      }
      $keep
    } #End of where Object
  
}#End for Foreach loop

Output
but i want this kept in file 1
but i want this kept in file 2

Answer 1

To keep in line with the code you linked to, you can adjust that to do what I think you want it to do:

# set the start and end lines for deletion here.
# we will use the '-like' operator with a wildcard '*' appended, so these strings
# should be at the start of the line to compare. (Case-Insensitive)
$startDelete = 'I want this deleted'
$stopDelete  = 'but i want this kept in file'

# get a list of files that need updating and loop through
# assuming all files have a '.txt' extension. If not, change that in the filter
$files = Get-ChildItem -Path 'D:\Test' -Filter '*.txt' -File
foreach ($file in $files) {
    Write-Host "Processing file $($file.FullName)"
    # set the $keep variable to $true to start off
    $keep = $true
    # collect every line we want to keep in a variable $content
    $content = Get-Content -Path $file.FullName | ForEach-Object {
        if ($_ -like "$startDelete*") {
            # set the $keep variable to $false and do not output this line
            $keep = $false
        }
        elseif ($_ -like "$stopDelete*") {
            # set the $keep variable to $true so the line, 
            # represented by automatic variable '$_' gets output
            $keep = $true
        }
        # all lines are either blocked or output, depending on the value of $keep
        if ($keep) { $_ }
    }

    # we can now overwrite the original file with the new content
    Set-Content -Path $file.FullName -Value $content
}

^{I've added code comments to help understanding what is going on}

Answer 2

First, your example Foreach-Object loop is not valid. You are not providing anything for it to loop. You can either pipe the files in or pass to the -InputObject parameter.

Next, when using Get-Content in a pipeline while trying to write, the reading needs to be completely finished. One simple way of ensuring this is to surround it with parentheses.

(Get-Content $files) | ...

However, since you want to read from and write to different files, this approach isn't right. You will be collecting the content from all files with the command above.

Lastly, instead of excluding the lines you don't want, I suggest just including the line(s) you do want. Based on your example you are looking for the line that begins with but. We can use a switch statement to read the file and process the lines. I am using regex with this example, but it can also be used without regex.

$files = Get-ChildItem 

$files | Foreach-Object {
    $output = Switch -Regex -File $_.fullname {
        'but' {$_}
    }
    $output | Set-Content $_.fullname
}#End for Foreach loop

This will read each file one at a time, return any line starting with but, captured in the $output variable, and finally we write that back to the same file.

Here is an alternative way to using regex

$files = Get-ChildItem 

$files | Foreach-Object {
    $output = Switch -File $_.fullname {
        {$_.startswith('but')} {$_}
    }
    $output | Set-Content $_.fullname
}#End for Foreach loop

Answer 3

You are way over complicating this. It's ok to be new, but always see the help files and the examples there or even videos on Youtube.

This is all in the Powershell help files.

# Get specifics for a module, cmdlet, or function
(Get-Command -Name Get-Help).Parameters
(Get-Command -Name Get-Help).Parameters.Keys
Get-help -Name Get-Help -Examples
Get-help -Name Get-Help -Full
Get-help -Name Get-Help -Online

https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/set-content?view=powershell-7.1

***Example 3: *** Replace text in a file

This command replaces all instances of word within an existing file.

Get-Content -Path .\Notice.txt

Warning
Replace Warning with a new word.
The word Warning was replaced.

(Get-Content -Path .\Notice.txt) |
    ForEach-Object {$_ -Replace 'Warning', 'Caution'} |
        Set-Content -Path .\Notice.txt
Get-Content -Path .\Notice.txt

Caution
Replace Caution with a new word.
The word Caution was replaced.