Replacing $_ substring value in powershell

Question

I am trying to make further use of a wonderful piece of code I found when I tried to replace text at a specified line.

However trying to get it to read $_.Substring() and then using $_ -replace is giving me troubles; although I get no error messages the text does not get replaced.

Here is code that does not work:

$content = Get-Content Z:\project\folder\subfolder\newindex2.html
$content | 
ForEach-Object { 
if ($_.ReadCount -ge 169 -and $_.ReadCount -le 171) { 
  $a = $_.Substring(40,57)
  $linked = '<a href="http://tempsite.info/folder1/folder2/' + $a + '">' + $a + '</a>'
  $_ -replace $a,$linked
} else { 
  $_ 
} 
} | 
Set-Content Z:\project\folder\subfolder\newindex2.html

The whole point is to make the content of a cell in a html table column link to a file on a webserver with the same name as what's in the cell.

I didn't have any luck trying my hand at regex trying to match the filenames, but since I managed to make it so the text that's to be replaced always ends up at the same position, I figured I'd try positional replacement instead. The text that is to be replaced is always 57 characters long and always starts at position 40.

I looked at the variables getting set, and everything gets set correctly, except that

$_ -replace $a,$linked

does not replace anything. Instead, the whole file just gets written anew with nothing changed. Can anyone please point to what I am missing and/or point to how to reach the result more easily? Maybe I'm using Substring wrong and should be using something else?

What does `$a` look like? Does it have special regex charaters in the string. That would prevent the match you are looking for. I would like to see what those 3 lines look like from a sample file first. — Matt, Sep 12 '15 at 14:56
Also, If you already know what you are replacing you dont even need regex at all. I would need to see $a I think before I could answer — Matt, Sep 12 '15 at 15:01

Mathias R. Jessen · Accepted Answer · 2015-09-12T15:48:37.267

1

The first item in the right-hand argument of -replace is a regex pattern, so depending on what the substring contains, some of the characters might be regex control characters.

You can either escape it:

$_ -replace $([regex]::Escape($a)),$linked

Or use the String.Replace() method, which does not use regex:

$_.Replace($a,$linked)

Finally, as @Matt points out, you might want to avoid the find-and-replace approach altogether, since you already know at which character indices you need to insert your new value:

$_.Remove(40,57).Insert(40,$linked)

edited Sep 12 '15 at 15:48

answered Sep 12 '15 at 13:05

Mathias R. Jessen

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This is not right. There is a readcount property. Use GM and you will see. After reading it seems clear what he is doing. His replace is what is question – Matt Sep 12 '15 at 14:54
This last edit after @Matt made their point resolved the issue. Many thanks! :) – Chokehold Sep 12 '15 at 17:01

Replacing $_ substring value in powershell

1 Answers1