arrays - PowerShell regex to extract SID from filename -

i have array $vhdlist contents similar following filenames:

uvhd-s-1-5-21-8746256374-654813465-374012747-4533.vhdx uvhd-s-1-5-21-8746256374-654813465-374012747-6175.vhdx uvhd-s-1-5-21-8746256374-654813465-374012747-8147.vhdx uvhd-template.vhdx 

i want use regex , left array containing sid portion of filenames.

i using following:

$sids = foreach ($file in $vhdlist)  { [regex]::split($file, '^uvhd-(?:([(\d)(\w)-]+)).vhdx$') } 

there 2 problems this: in resulting array there 3 blank lines every sid; , "template" filename matches (the resulting line in output "template"). how can array of sids output , not include "template" line?

you seem want filter list down filenames contain sid. filtering done where-object (where short); don't need loop.

an sid described "s- , bunch of digits , dashes" simple case. leaves ^uvhd-s-[\d-]*\.vhdx$ filename.

in combination get:

$vhdlist | { $_ -match "^uvhd-s-[\d-]*\.vhdx$" } 

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when don't have array of strings, array of files, use them directly.

dir c:\some\folder | { $_.name -match "^uvhd-s-[\d-]*\.vhdx$" } 

or, possibly can make simple as:

dir c:\some\folder\uvhd-s-*.vhdx 

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edit

extracting sids list of strings can thought combined transformation (for each element, extract sid) , filter (remove non-matches) operation.

powershell's foreach-object cmdlet (foreach short) works map() in other languages. takes every input element , returns new value. in effect transforms list of input elements output elements. -replace operator can extract sids way.

$vhdlist | foreach { $_ -replace ^(?:uvhd-(s-[\d-]*)\.vhdx|.*)$,"`$1" } | { $_ -gt "" } 

^{the regex back-reference .net languages $1. $ special character in powershell strings, needs escaped, except when there no ambiguity. backtick ps escape character. can escape $ in regex well, there it's not necessary.}

as final step use where remove empty strings (i.e. non-matches). doing way around means need apply regex once, instead of 2 times when filtering first , replacing second.

powershell operators can work on lists directly. above shortened:

$vhdlist -replace "^uvhd-(s-[\d-]*)\.vhdx$","`$1" | { $_ -gt "" } 

the shorter version works on lists of actual strings or objects produce right thing when .tostring() called on them.

regex breakdown:

 ^                       # start-of-string anchor (?:                     # begin non-capturing group (either...)   uvhd-                 #   'uvhd-'   (                     #   begin group 1     s-[\d-]*            #     's-' , many digits , dashes   )                     #   end group 1   \.vhdx                #   '.vhdx'   |                     #    ...or...   .*                    #   else )                       # end non-capturing group $                       # end-of-string anchor