Trim end of string - regex

Question

I'm having trouble trimming off some characters at the end of a string. The string usually looks like:
C:\blah1\blah2
But sometimes it looks like:
C:\blah1\blah2.extra
I need to extract out the string 'blah2'. Most of the time, that's easy with a substring command. But on the rare occasions when the '.extra' portion is present, I need to first trim that part off.
The thing is, '.extra' always begins with a dot, but then is followed by various combinations of letters with various lengths. So wildcards will be necessary. Essentially, I need to script, "If the string contains a dot, trim off the dot and anything following it."
$string.replace(".*","") doesn't work. Nor does $string.replace(".\*",""). Nor does $string.replace(".[A-Z]","").
Also, I can't get at it from the beginning of the string either. 'blah1' is unknown and of various lengths. I have to get at 'blah2' from the end of the string.

Answer 1

Assuming that the string is always a path to a file with or without an extension (such as ".extra"), you can use Path.GetFileNameWithoutExtension():
PS C:\> [System.IO.Path]::GetFileNameWithoutExtension("C:\blah1\blah2")
blah2
PS C:\> [System.IO.Path]::GetFileNameWithoutExtension("C:\blah1\blah2.extra")
blah2
The path doesn't even have to be rooted:
PS C:\> [System.IO.Path]::GetFileNameWithoutExtension("blah1\blah2.extra")
blah2
If you want to implement similar functionality on your own, that should be fairly simply as well - use String.LastIndexOf() to find the last \ in the string and use that as your starting argument for Substring():
function Extract-Name {
param($NameString)
# Extract part after the last occurrence of \
if($NameString -like '*\*') {
$NameString = $NameString.Substring($NameString.LastIndexOf('\') + 1)
}
# Remove anything after a potential .
if($NameString -like '*.*') {
$NameString.Remove($NameString.IndexOf("."))
}
$NameString
}
And you'll see similar results:
PS C:\> Extract-Name "C:\blah1\blah2.extra"
blah2
PS C:\> Extract-Name "C:\blah124323\blah2.extra"
blah2
PS C:\> Extract-Name "C:\blah124323\blah2"
blah2
PS C:\> Extract-Name "abc124323\blah2"
blah2

Answer 2

As the other posters have said, you can use special file name manipulators for this. If you'd like to do it with regular expressions, you can say
$string.replace("\..*","")
The \..* regex matches a dot (\.) and then any string of characters (.*).
Let me address each of the non-working regexes individually:
$string.replace(".*","")
The reason this doesn't work is that . and * are both special characters in regular expressions: . is a wildcard character that matches any character, and * means "match the previous character zero or more times." So .* means "any string of characters."
$string.replace(".\*","")
In this instance, you're escaping the * character, meaning that the regex treats it literally, so the regex matches any single character (.) followed by a star (\*).
$string.replace(".[A-Z]","")
In this case, the regex will match any character (.) followed by any single capital letter ([A-Z]).

Answer 3

If the strings are actual paths using Get-Item would be another option:
$path = 'C:\blah1\blah2.something'
(Get-Item $path).BaseName
The Replace() method can't be used here, because it doesn't support wildcards or regular expressions.