delete a specific line in file with powershell

Question

I want to delete a complete line which contains a special word in a single .csv file in a powershell script.

I already found working code, that deletes the specific line, but writes all other lines into the first line. This shouldn't happen, because I linked the csv-file with an ms access table.

    $user = 'User2'
    $file = Get-Content c:\datei.txt
    $newLine = ""

    foreach($line in $file){

        if($line -match $User){
         }else{
            $newLine += $line
        }
    }
    $newLine | Out-File c:\datei.txt

The file looks like this, but with more data and lines:

User;computer;screen1;screen2;printer
User1;bla;bla;;bla
User2;bla;bla;bla;bla
User3;bla;bla;bla;bla

After running the code:

User;computer;screen1;screen2;printerUser1;bla;bla;;blaUser3;bla;bla;bla;bla

I use Powershell 5.1.x on Windows 7

TessellatingHeckler · Accepted Answer · 2018-04-27 07:34:36Z

6

It happens because you're doing string concatenation.

$newLine = ""
$newLine += $line

# result is exactly how it looks,  
# "" -> "line1" -> "line1line2" -> "line1line2line3" ...

The straightforward fix is to use an array:

$newLine = @()
$newLine += $line

# result is adding lines to an array  
# @() -> @("line1") -> @("line1","line2") -> @("line1","line2","line3") ...

but the proper PowerShell way is not to do that at all, and to stream the file through your code and out into another file:

$user = 'User2'
$file = Get-Content c:\datei.txt

foreach($line in $file){

    if($line -match $User){
     }else{
        $line   # send the line to the output pipeline
    }

} | Out-File c:\datei.txt

But you can invert the test -match to -notmatch and get rid of the empty {} part.

$user = 'User2'
$file = Get-Content c:\datei.txt

foreach($line in $file){

    if($line -notmatch $User){
        $line   # send the line to the output pipeline
    }

} | Out-File c:\datei.txt

And you can get rid of temporarily storing the file content:

$user = 'User2'
Get-Content c:\datei.txt | ForEach-Object {

    if ($_ -notmatch $User){
        $line   # send the line to the output pipeline
    }

} | Out-File c:\datei.txt

But then it's just acting as a filter, and you can change foreach-object / if() {} for a where-object filter:

$user = 'User2'
Get-Content c:\datei.txt | Where-Object {

    $_ -notmatch $User

} | Out-File c:\datei.txt

And then change Out-file for Set-Content (the pairing is get-content/set-content, and it gives more control over output encoding if you need it):

$user = 'User2'

Get-Content c:\datei.txt | 
    Where-Object { $_ -notmatch $User } | 
    Set-Content c:\datei.txt

answered Apr 27, 2018 at 7:34

TessellatingHeckler

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2 Comments

SysCrasher Over a year ago

Thank you. I tried your last suggestion and it also worked. i only had to add brackets, because it says the file was already in use ` (Get-Content c:\datei.txt | Where-Object { $_ -notmatch $User }) | Set-Content c:\datei.txt `

TessellatingHeckler Over a year ago

Good catch, I forgot about that happening when overwriting the same file! That makes it a bit uglier, and you may as well do $lines = get-content c:\datei.txt then $lines | where-object {...} | set-content .. really.

boxdog · Accepted Answer · 2018-04-27 07:31:54Z

0

You need to add a 'newline' to the end of each line of text. Change this line:

$newLine += $line

to:

$newLine += "$line`r`n"

answered Apr 27, 2018 at 7:31

boxdog

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1 Comment

SysCrasher Over a year ago

It works, thank you. I was sure, that this `n or something similar was missing somewhere in this line. But i didn't knew, that I have to place this into "".

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