PowerShell finding a file and creating a new one - variables

Question

The script I'm working on is producing a log file every time it runs. The problem is that when the script runs in parallel, the current log file becomes inaccessible for Out-File. This is normal because the previous script is still writing in it.
So I would like the script being able to detect, when it starts, that there is already a log file available, and if so, create a new log file name with an increased number between the brackets [<nr>].
It's very difficult to check if a file already exists, as it can have another number each time the script starts. It would be great if it could then pick up that number between the brackets and increment it with +1 for the new file name.
The code:
$Server = "UNC"
$Destination ="\\domain.net\share\target\folder 1\folder 22"
$LogFolder = "\\server\c$\my logfolder"
# Format log file name
$TempDate = (Get-Date).ToString("yyyy-MM-dd")
$TempFolderPath = $Destination -replace '\\','_'
$TempFolderPath = $TempFolderPath -replace ':',''
$TempFolderPath = $TempFolderPath -replace ' ',''
$script:LogFile = "$LogFolder\$(if($Server -ne "UNC"){"$Server - $TempFolderPath"}else{$TempFolderPath.TrimStart("__")})[0] - $TempDate.log"
$script:LogFile
# Create new log file name
$parts = $script:LogFile.Split('[]')
$script:NewLogFile = '{0}[{1}]{2}' -f $parts[0],(1 + $parts[1]),$parts[2]
$script:NewLogFile
# Desired result
# \\server\c$\my logfolder\domain.net_share_target_folder1_folder22[0] - 2014-07-30.log
# \\server\c$\my logfolder\domain.net_share_target_folder1_folder22[1] - 2014-07-30.log
#
# Usage
# "stuff" | Out-File -LiteralPath $script:LogFile -Append

Answer 1

As mentioned in my answer to your previous question you can auto-increment the number in the filename with something like this:
while (Test-Path -LiteralPath $script:LogFile) {
$script:LogFile = Increment-Index $script:LogFile
}
where Increment-Index implements the program logic that increments the index in the filename by one, e.g. like this:
function Increment-Index($f) {
$parts = $f.Split('[]')
'{0}[{1}]{2}' -f $parts[0],(1 + $parts[1]),$parts[2]
}
or like this:
function Increment-Index($f) {
$callback = {
$v = [int]$args[0].Groups[1].Value
$args[0] -replace $v,++$v
}
([Regex]'\[(\d+)\]').Replace($f, $callback)
}
The while loop increments the index until it produces a non-existing filename. The parameter -LiteralPath in the condition is required, because the filename contains square bracket, which would otherwise be treated as wildcard characters.