Powershell - Check IP, loop to retry and send email - powershell

Question

I've been trying to script so powershell checks our external ip - if its unchanged - do nothing just log its been checked.
If the script thinks its changed, retry, and if after 5 attempts it has changed then send an email.
I've included where I got to, but I can't (tiredness or stupidity) get this to work today so throwing this out to the hive mind for help!
attached is where ive got too! Cheers CM
#find old ip
$oldip = gc .\ip.txt
#get current ip address
$currentip = (New-Object net.webclient).downloadstring("http://api.ipify.org")
#current date and time
$currentTime = Get-Date -format "dd-MMM-yyyy HH:mm:ss"
#script location
$scriptpath = $MyInvocation.MyCommand.Definition
[string]$dir = Split-Path $scriptpath
set-location $dir
#set the smtp server URL here
$smtpServer = "smtp.my.com"
#Set the Sender Name or Email here
$sender = "sender#my.comm"
#Enter the email reciepients here - you can send to multiple using format: "user1#gmail.com", "user2#hotmail.com";
$users = "email#my.com";
#Enter the subject title the reciepient see's here
$subject = "IP Has Changed"
#Type out the email contents here
$body = "Dear Team Member,
Your IP address at has just changed from: $oldip
And is now set too: $currentip
Regards."
#*****************************************************************************************************************************************
do {
$Result = ($oldip -ne $currentip)
if ($Result.Status -eq "Success") {
Write-Output "IP Address Unchanged - Monitoring Continues."
Add-Content $PSScriptRoot\IP_Check_Log.txt "$currentTime - IP Unchanged. "
Start-Sleep -s 2
Exit 0
}
else {
Write-Output "Ping Failed!"
Add-Content $PSScriptRoot\IP_Check_Log.txt "$currentTime - IP Check Failed - Retrying"
$Failures += 5
}
} until ($Failures -ge $FailureThreshold)
Write-Output "IP Address Changed!"
Add-Content $PSScriptRoot\IP_Check_Log.txt "$currentTime - IP Adderss Changed. "
Add-Content $PSScriptRoot\IP_Check_Log.txt "*****************************************************************************"
#be sure to alter the SMTP server port here if needed.
$smtp = New-Object Net.Mail.SmtpClient($smtpServer, 587)
$smtp.EnableSsl = $true
#Enter the sending email address and password here
$smtp.Credentials = New-Object System.Net.NetworkCredential("email#my.com", "password");
$smtp.Send($sender, $user, $subject, $body)

Answer 1

Perhaps easier than a do{..} until(..) here is to loop using a for loop and I would use a try{..} catch{..} on this.
Inside the loop get the ip address fresh, don't get that once and keep looping over that instance.
Something like this perhaps (left out the emailing stuff)
$logFile = Join-Path -Path $PSScriptRoot -ChildPath 'IP_Check_Log.txt'
$FailureThreshold = 5
# find old ip
$oldip = [IPAddress](Get-Content .\ip.txt)
$ipchanged = $false
$currentip = $null
for ($i = 0; $i -lt $FailureThreshold; $i++) {
try {
# try to get the get current ip address
$currentip = [IPAddress](New-Object net.webclient).DownloadString("http://api.ipify.org")
if ($currentip -eq $oldip) {
Write-Output "IP Address Unchanged - Monitoring Continues."
Add-Content -Path $logFile -Value "$currentTime - IP Unchanged. "
exit 0
}
else {
$ipchanged = $true
}
}
catch {
$currentip = $null
$ipchanged = $false
Write-Output "Ping Failed!"
Add-Content -Path $logFile -Value "$currentTime - IP Check Failed - Retrying"
}
Start-Sleep -Seconds 2
}
# test if the above returned a $currentip not $null and if boolean $ipchanged is $true
if (($currentip) -and $ipchanged) {
Write-Output "IP Address Changed!"
Add-Content -Path $logFile -Value "$currentTime - IP Address Changed. "
Add-Content -Path $logFile -Value "*****************************************************************************"
# refresh the .\ip.txt file to store the new ip?
Set-Content -Path .\ip.txt -Value $currentip.IPAddressToString
# send the email
}
I use casts to [IPAddress] because if the .DownloadString() fails OR it returns something which is not an IP address, you will enter the catch block so you can deal with the error