[Regex]::Match() behaving differently inside vs outside an If (that also uses [Regex]::Match() )

Question

Given a uninstallString of "C:\ProgramData\Package Cache\{56e11d69-7cc9-40a5-a4f9-8f6190c4d84d}\VC_redist.x86.exe" /uninstall I can successfully extract the quoted text with ([Regex]::Match($uninstallString, '^\".*\"').Value). however, if I test to see if the string has the required /uninstall bit, then try to extract the quoted bit, like this...

if ([Regex]::Match($uninstallString, '^\".*\" +/uninstall').Succes) {
    ([Regex]::Match($uninstallString, '^\".*\"').Value)
}

Instead of the value being the full string, it's only returning "C:\ProgramData\Package. Now, My understanding is that . is everything but a line break, so it should be OK with the space. But, if I replace the space with an underscore in the string it works as expected, so it's definitely the space causing the issue. Also, I am confused why it works outside of the If, but not inside. I was under the impression that using [Regex]::Match() creates individual objects with each use, that wouldn't interact with each other, but here it seems they are.

FYI, you don't need to escape quotes in regex. They don't have special meaning. Also, you should be using `[Regex]::IsMatch` — Maximilian Burszley, Aug 19 '18 at 19:52
Unable to reproduce this, is this the actual code you're using? (there's a typo in your example btw, it's `Success`, not `Succes`) — Mathias R. Jessen, Aug 19 '18 at 19:52
As a best-practice, I'd suggest using the `-match` comparison operator and the `$matches` automatic variable. — Maximilian Burszley, Aug 19 '18 at 19:53
@TheIncorrigible1 I have been using -match, but I find needing multiple lines to extract one bit of data "annoys" me. Curious what the reason for -match being best practice is? That said, the named captures approach Theo mentions is really interesting. Good stuff to learn! — Gordon, Aug 19 '18 at 20:49

score 0 · Answer 1 · answered Aug 19 '18 at 20:14

Since you want to see if the quoted string (path) is found AND if it contains a switch '/uninstall' or not, I'd do something like this:

$uninstallString = '"C:\ProgramData\Package Cache\{56e11d69-7cc9-40a5-a4f9-8f6190c4d84d}\VC_redist.x86.exe"'

if ($uninstallString -match '^(?<path>".*")(?:\s+(?<switch>/uninstall))?') {
    $uninstallPath   = $matches['path']    # at least the path (quoted string) is found
    $uninstallSwitch = $matches['switch']  # if '/uninstall' switch is not present, this will result in $null
}

[Regex]::Match() behaving differently inside vs outside an If (that also uses [Regex]::Match() )

1 Answers1