Powershell RegEx match negative lookbehind at start of string

Question

I'm currently working on a WSUS-Update automization and I'd like to get all Updates that don't start with "(German|English) Language Pack".

This is what I got so far:

[regex]$reg = "(?<!German|English|English \(United States\)) Language Pack"
$LanguagePacks = $updates.Where({ $_.Title -match $reg })

That works, but I also get updates like: Windows Internet Explorer 9 Language Pack for Windows 7 for x64-based Systems

But I also want to get Updates in the following syntax: [Language] Language Pack e.g. Finnish Language Pack

So I tried to use the '^' anchor to determine the start of the String

[regex]$reg = "^(?<!German|English|English \(United States\)) Language Pack"
$LanguagePacks = $updates.Where({ $_.Title -match $reg })

But in this case the result is empty :(

Answer 1

You may use

(?<!^(?:German|English(?:\s+\(United States\))?)\s*)Language Pack

See the regex demo

It matches Language Pack if it is not preceded with German, English, or English (United States) at the start of the string.

Details

• (?<! - start of a negative lookbehind that fails the match if, immediately to the left of the current location, there are patterns:
  • ^ - start of string
  • (?: - start of an alternation non-capturing group:
    • German - a literal substring
    • | - or
    • English - a literal substring
    • (?:\s+\(United States\))? - an optional non-capturing group matches 1 or 0 occurrences of:
      • \s+ - 1 or more whitespaces
      • \(United States\) - a literal (United States) substring
  • ) - end of the alternation group
  • \s* - 0+ whitespaces
• ) - end of the lookbehind
• Language Pack - a literal substring