Best Practice - If match return result - powershell

Question

Use Case
The below script is to be placed in a scheduled task to notify me if my public IP Address changes
The IF match condition is not the correct behaviour
What would be the best way to match if the IP Address changed and output that to host?
Code
$ip = Invoke-RestMethod http://ipinfo.io/json | select -ExpandProperty ip
$date = (get-date).date
$value = "{0} - {1}" -f ($date),($ip)
Add-Content -Value $value -Path "C:\users\Sumeet\Documents\WindowsPowerShell\ip.txt"
$file = Get-Content -Path "C:\users\Sumeet\Documents\WindowsPowerShell\ip.txt"
if ($file | Select-String -Pattern $ip) {
clear-host
write-host "Match found at $_ your public IP interface has changed"
}
File Output
Date - IP
9/06/2018 12:00:00 AM - 121.211.177.20
9/06/2018 12:00:00 AM - 121.211.177.20
Output

Answer 1

I think something similar would be more helpful, as #LotPings suggested. You should update the file only if there is a change and follow up with notification as needed.
Also note, that change of IP can occur at anytime, but your scheduled task will let you know only whenever it is scheduled to run.
$ip = Invoke-RestMethod http://ipinfo.io/json | select -ExpandProperty ip
$date = (get-date).date
$value = "{0} - {1}" -f ($date),($ip)
$file = Get-Content -Path "E:\Code\powershell\myPS\2018\Jun\checkPublicIP\ip.txt"
if ($file | Select-String -Pattern $ip) {
Write-Host "IP is not changed"
}
else {
#Adding current IP to the file
Add-Content -Value $value -Path "E:\Code\powershell\myPS\2018\Jun\checkPublicIP\ip.txt"
#Add more code as needed for notification / email / alert.
}

Answer 2

Handling of data is IMO done easier when using csv files as columns/properties are assigned on import.
Because of my locale which doesn't support the date separator / or tt for AM/PM I had to use a CultureInfo object.
## Q:\Test\2018\06\09\SO_50771712.ps1
$File = "$Env:USERPROFILE\Documents\WindowsPowerShell\ip.csv"
$CIUS = New-Object System.Globalization.CultureInfo("en-US")
$Actual = [PSCustomObject]#{
Date = (get-date).ToString("d/M/yyyy hh:mm:ss tt",$CIUS)
IP = (Invoke-RestMethod http://ipinfo.io/json).ip
}
if (!(Test-Path $File)){'"Date","IP"'|Set-Content $File}
$Last=Import-Csv $File|Sort-Object {[DateTime]$_.Date}|Select-Object -Last 1
If ($Last.ip -ne $Actual.ip){
Write-Host ("Last ip : {0} from: {1}" -f $LAst.IP,$Last.date)
Write-Host ("New ip : {0} from: {1}" -f $Actual.IP,$Actual.date)
Export-Csv $File -InputObject $Actual -Append -NoTypeInformation
}
Sample output:
> Q:\Test\2018\06\09\SO_50771712.ps1
Last ip : 92.123.13.83 from: 9/6/2018 09:19:21 PM
New ip : 92.123.13.84 from: 9/6/2018 09:34:59 PM
> gc $file
"Date","IP"
"9/6/2018 08:51:00 PM","92.123.13.82"
"9/6/2018 09:19:21 PM","92.123.13.83"
"9/6/2018 09:34:59 PM","92.123.13.84"