PowerShell Username Generator - Add to File/Check Against - powershell

Question

I am creating usernames as such: first 3 letters of the first name then 4 randomly generated numbers. Ryan Smith = RYA4859. I am getting the random number from this PowerShell command:
Get-Random -Minimum 1000 -Maximum 10000
I need to know how to create a script that will add the username to a .txt file after it has been generated. I also want the script to first check the .txt file to see if the randomly generated number already already exists and if it does, generate a new 4 digit number that does not exist and then add that to the .txt file.
The flow should be:
generate random 4 digit number
check txt file if number exists
if yes - generate new number
if no - append file and add generated number to file

Answer 1

You want to run a do...until loop that runs until the randomly generated number doesn't exist in your text file
$file = "C:\users.txt"
$userId = "RYA"
# get the contents of your text file
$existingUserList = Get-Content $file
do
{
$userNumber = Get-Random -Minimum 1000 -Maximum 10000
# remove all alpha characters in the file, so only an array of numbers remains
$userListReplaced = $existingUserList -replace "[^0-9]" , ''
# the loop runs until the randomly generated number is not in the array of numbers
} until (-not ($userNumber -in $userListReplaced))
# concatenates your user name with the random number
$user = $userId + $userNumber
# appends the concatenated username into the text file
$user | Out-File -FilePath $file -Append
Without the 3 character prefix
$file = "C:\users.txt"
# get the contents of your text file
$existingUserList = Get-Content $file
do
{
$userNumber = Get-Random -Minimum 1000 -Maximum 10000
# remove all alpha characters in the file, so only an array of numbers remains
$userListReplaced = $existingUserList -replace "[^0-9]" , ''
# the loop runs until the randomly generated number is not in the array of numbers
} until (-not ($userNumber -in $userListReplaced))
# appends the concatenated username into the text file
$userNumber| Out-File -FilePath $file -Append

Answer 2

Note: Hashtables in general will find keys in less time than finding a matching element in an unsorted array. This difference in performance increases as the number of elements increase. While a binary search on a sorted arrays may come closer in performance, the sorting process itself can be be a major performance hit and add complexity to the code.
The main difference between the described version of the code in the comment on the question, and the following code, is that I'm appending the new user name to the file instead of over writing the file, and added a loop near the end to repeatedly ask if the code should continue.
function RandomDigits {
[CmdletBinding()]
param (
[Parameter()]
[int]$DigitCount = 2
)
$RandString = [string](Get-Random -Minimum 100000 -Maximum 10000000)
$RandString.Substring($RandString.Length-$DigitCount)
}
function GenUserName {
[CmdletBinding()]
param(
[Parameter(Mandatory = $true, Position = 0)]
[string]$Prefix
)
"$Prefix$(RandomDigits 4)"
}
function ReadAndMatchRegex {
[CmdletBinding()]
param(
[Parameter(Mandatory = $true, Position = 0)]
[string]$Regex,
[Parameter(Mandatory = $true, Position = 1)]
[string]$Prompt,
[Parameter(Mandatory = $false, Position = 2)]
[string]$ErrMsg = "Incorrect, please enter needed info (Type 'exit' to exit)."
)
$FirstPass = $true
do {
if (-not $FirstPass) {
Write-Host $ErrMsg -ForegroundColor Red
Write-Host
}
$ReadText = Read-Host -Prompt $Prompt
$ReadText = $ReadText.ToUpper()
if($ReadText -eq 'exit') {exit}
$FirstPass = $false
} until ($ReadText -match $Regex)
$ReadText
}
$Usernames = #{}
$UsernameFile = "$PSScriptRoot\Usernames.txt"
if(Test-Path -Path $UsernameFile -PathType Leaf) {
foreach($line in Get-Content $UsernameFile) { $Usernames[$Line]=$true }
}
do {
Write-Host
$UserPrefix = ReadAndMatchRegex '^[A-Z]{3}$' "Please enter 3 letters for user's ID"
do {
$NewUserName = GenUserName $UserPrefix
} while ($Usernames.ContainsKey($NewUserName))
$NewUserName | Out-File $UsernameFile -Append
$UserNames[$NewUserName]=$true
$UserNames.Keys
$Continue = ReadAndMatchRegex '^(Y|y|YES|yes|Yes|N|n|NO|no|No)$' 'Continue?[Y/N]'
} while ($Continue -match '^(Y|y|YES|yes|Yes)$')