Using Regex for complicated naming convention - regex

Question

I'm writing a Computer naming convention validation PowerShell script. I'm following a documentation my client provided. My first path I went down was to break each computer name into bits and process each part, but I seem to have issues near the end. I was thinking it would be easier to just use one regex to ensure its valid. Here is what I am trying to do
Naming rules:
Required: 1st is an alpha character; must be: A,B, or C
Required: 2nd s an alpha character; must be: L,K, or H
Required: The next 4 characters must be alpha and match either: DTLB,SOCK, or NUUB
Required: The next 6 characters are digits but the first part can either be: 1, 8, 13, or 83; the rest doesn't matter as long as they are digits
Optional: The next two characters can be alpha or alpha numeric but must be either: PE, Y1, or AC
Here are some tests with a regex that I understand, which is basic but works. It doesn't validate the actual characters or position, it just checks the first 12 characters and if there are two alphas characters at the end:
$regex = '^\w{12}(?:\w{2})$|^\w{12}$'
'AKDTLB123456' -match $regex; $Matches
True
'ALSOCK834561PE' -match $regex; $Matches
True
What I am trying to do is split these up into named parts and determine if the value matches the right area like (this is an example):
$regex = '(<type>^\w{1}[ABC])(?<form>\w{1,1}[LKH])(<locale>\w{4,4}[DTLB|SOCK|NUUB])(<identifier>\d{1,1}[1|8]|<identifier>\d{1,2}[13|83])(<unique>\d+)(<role>\w{2,2}[PE|AC]$|<role>\w{1}[Y]\d{1}$)'
My goal is to get it to output like this:
Example 1
'AKDTLB893456' -match $regex; $Matches
True
Name Value
---- -----
type A
form K
locale DTLB
identifier 1
Unique 23456
0 AKDTLB893456
Example 2:
'ALSOCK123456PE' -match $regex; $Matches
True
Name Value
---- -----
type A
form L
locale SOCK
identifier 1
Unique 23456
0 ALSOCK123456PE
Example 3
'ALSUCK123456PE' -match $regex; $Matches
False
Name Value
---- -----
type A
form L
locale <--not matched
identifier 1
Unique 23456
0 ALSuCK123456PE
The best I can do is:
$regex = '(^\w{1})(\w{1,1})(\w{4,4})(\d{2}[13|83]|\d{1}[1|2|3])(\d{4,5})(\w{2,2}$|$)'
'ALSOCK124561PE' -match $regex; $Matches
True
Name Value
---- -----
6 PE
5 4561
4 12
3 SOCK
2 L
1 A
0 ALSOCK834561PE
However this doesn't check for if the name is just 112345 not 13
I have been all over the internet and using the regex online tool, but am unable to come up with a solution. This may not be possible to do both. I find if the value is false, its not outputting the one that match and not the rest. Is there a way to get the "why it doesn't match" as an output?
Any ideas?

Answer 1

You may use
^(?<type>[ABC])(?<form>[LKH])(?<locale>DTLB|SOCK|NUUB)(?<identifier>[18](3)?)(?<unique>\d{4}(?(1)|\d))(?<role>PE|Y1|AC)?$
Note: If the pattern must be matched in a case sensitive way, replace -match with -cmatch.
See the .NET regex demo (do not test at regex101.com!)
Details
^ - start of a string
(?<type>[ABC]) - Group "type": A, B or C
(?<form>[LKH]) - Group "type": L, K or H
(?<locale>DTLB|SOCK|NUUB) - Group "locale": DTLB, SOCK or NUUB
(?<identifier>[18](3)?) - Group "identifier": 1 or 8 and then an optional 3 digit captured into Group 1
(?<unique>\d{4}(?(1)|\d)) - Group "unique": four digits and if Group 1 did not match, one more digit is required to match then
(?<role>PE|Y1|AC)? - an optional Group "role": PE, Y1 or AC
$ - end of string.

Answer 2

The second part of your question asked if you could determine where the match failed. You can do something similar to below to test each part of the regex in sections starting from the left:
$strings = 'AKDTLB893456','ALSOCK123456PE','ALSuCK123456PE','ALSOCK123456R2'
$regexes = [ordered]#{}
$regexes.Add('type','^(?<type>[ABC])')
$regexes.Add('form','(?<form>[LKH])')
$regexes.Add('locale','(?<locale>DTLB|SOCK|NUUB)')
$regexes.Add('identifier','(?<identifier>[18])')
$regexes.Add('unique','(?<unique>\d{5})')
$regexes.Add('optional','(?<optional>PE|Y1|AC)?$')
foreach ($string in $strings) {
$test = [text.stringbuilder]''
$regexes.GetEnumerator() | Foreach-Object {
$null = $test.Append($_.Value)
if (!($string -match $test.ToString())) {
"$String failed at $($_.Key)"
Continue
}
}
$matches
}
Explanation:
$regexes is an ordered hash table where we can append some key-value pairs. Order is good here because we want to test matching from left to right in your string.
With a [Text.StringBuilder] object, we can append strings with the Append() method. The idea is to append the new regex string you want to test. If $string continues to match through each value of the hash table, $matches will output. Otherwise, the failed match will cause the current, testing $regex key value to output.
Note that this will not perform as well as a single -match operation. You could test the entire match first and only perform sectional testing when a $false is returned. That will increase performance.