Working with unusual date formats in Powershell? - powershell

Question

I am working on a GUI-based Powershell tool to help users easily find out when their AD password is going to expire. Due to Covid restrictions, most users and not on-site and rely on VPN to connect to AD. A by-product of this is that many do not see the automatic pop-up in Windows to remind them of them to set a new password soon. Those that are on-site see the notification OK. It's a not a group-policy problem. The tool will be will be rolled-out in two different languages - one representing the 'mothership' (where is English is not normally spoken) and English for all other countries.
Some of the (mostly) Eastern European countries use a short date format that reads like 'd.M.yyyy.' - according to settings menu when one changes the 'Region' setting in Windows.
The tool calculates the difference between today and the expiry data and outputs the number of days to a text field. The actual expiry is display correctly in its own text field.
Some of the source code behind it all...
$thisUser = [Environment]::UserName
#make string
"net user " + $thisUser + " /domain"
#make cmd string
$fetch_net_user = "net user " + $thisUser + " /domain"
#execute command and store to variable
$net_user_data_array = Invoke-Expression $fetch_net_user
#Gets password expiry date (with header)
$password_expiry_with_header = $net_user_data_array[11]
#extracts only the date and assigns to new variable (the hours and minutes) can be ignored)
$password_expiry_as_string = $password_expiry_with_header.Split(' ')[-2]
# Home countries - works OK
try{
$password_expiry_as_dateTime = [datetime]::ParseExact($password_expiry_as_string, 'dd.MM.yyyy', $null)
}
# Others - works OK
catch{
$password_expiry_as_dateTime = [datetime]::ParseExact($password_expiry_as_string, 'dd/MM/yyyy', $null)
# where problem occurs
catch{
$password_expiry_as_dateTime = [datetime]::ParseExact($password_expiry_as_string, 'd.M.yyyy.', $null)
}
finally{
#show GUI error window...
}
#fetch date... converted to yesterday to fix an off-by-one bug!
$today = Get-Date
$rightNow = $today.AddDays(-1)
#calc days left
$daysRemaining = (New-TimeSpan -Start $rightNow -End $password_expiry_as_dateTime).Day
# some other code follows, manipulating date values etc. Works with most date formats.
When executed the script will throw several errors.
The first is...
Exception calling "ParseExact" with "3" argument(s): "String was not recognized as a valid DateTime."
Others will follow such as
You cannot call a method on a null-valued expression.
As the difference between today and the expiry date cannot be calulated.
Is there any easy fix for this? I'd rather avoid having to write a long list of 'if' statments for each country/culture. Thanks!
I'm sure the code could be a little bit more elegant, and that will be addressed in a later version. Right now, getting it to work some of the more obscure date formats is my priority.
Something else that I should stress is that this tool works in a 'read only' capacity. No 'Set-Item' commands are used.
Regards,
WL

Answer 1

You have 2 problems:
Multiple date formats used interchangeably
Trailing dots on some strings
The first problem can be solved by passing multiple format strings to ParseExact() - it'll try each in order until it successfully parses the input string (or reaches the end of the list):
[datetime]::ParseExact($password_expiry_as_string, [string[]]#('dd.MM.yyyy', 'dd/MM/yyyy', 'dd.M.yyyy', 'd.M.yyyy'), $null, [System.Globalization.DateTimeStyles]::None)
The second problem can be solved by trimming trailing dots:
[datetime]::ParseExact($password_expiry_as_string.TrimEnd('.'), [string[]]#('dd.MM.yyyy', 'dd/MM/yyyy', 'dd.M.yyyy', 'd.M.yyyy'), $null, [System.Globalization.DateTimeStyles]::None)