Powershell uses of Select-String to filter a log file and example Regular Expressions for identifying IP addresses and IP spaces

Test-SelectStringExamples.ps1

#This regex matches anything that's like an IP address (even invalid ones)
$regexIPAddress = '\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b'

#This regex matches anything like an IP address that starts 10, 172 or 192
$regexIPSpace = '(10|172|192).\d{1,3}\.\d{1,3}\.\d{1,3}\b'

#Returns the first IP address in each line of the log file/s then sorts and removes duplicates.
Select-String -Path *.log -Pattern $regexIPAddress | ForEach-Object { $_.Matches } | % { $_.Value } | Sort-Object -Unique | Out-File 'UniqueIPs.txt'

#Returns from a selection of Log files any lines which match a certain string pattern
Select-String -Path ex*.log -Pattern "accountname" | Select -expandproperty line | Out-File 'matches.log'