PowerShell convert string to datetime

Fun with time in PowerShell

PowerShell makes it very easy to have fun with dates and time which is really handy, for example, when creating logs timestamps or genearting users expiration date in an AD environment.

# Get current date and add 30 days
[datetime]$expirationDate = (Get-Date).AddDays(30)

# Output
Wednesday, September 2, 2020 4:45:19 PMM

As you can guess from the strong typed variable expirationDate is a datetime object and such it supports properties and methods on of which is .ToString() which will convert object to a string.

# Get String from datetime
$expirationDate.ToString('MM/dd/yyyy')

09/02/2020

# Get date string in other formats
$expirationDate.ToString('dd.MM.yyyy')

# Swiss format
02.09.2020

$expirationDate.ToString('dd/MM/yyyy')

# Italian format
02/09/2020

From date to string and back

Converting from datetime to a string is easy but what if we have a date in string format, for example coming from a SQL query or an AD attribute, and we need to convert it back to a datetime objec to, say, perform comparison or calculations?

This is easily accomplished via the ParseExact method of the datetime object. Building from the previous exampel let’s assume our date string is 02/09/2020

# Parse and convert string
$testConversion = [datetime]::ParseExact('02/09/2020', 'dd/MM/yyyy', $null)

$testConversion

Wednesday, September 2, 2020 12:00:00 AM

# Get type
PS C:\Users\dc.sys> $testConversion.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     DateTime                                 System.ValueType

Note how the object has been converted to DateTime as expectted. A common pitfall in the process is the second argument to the ParseExact method as the specified date format must match that of the input string.

Note: Both arguments can of course be variables as long as they’re in the correct format and not $null

A neat feature of the ParseExact method is that you can even output another string with a different date format.

# Parse input and output string in the desired format
[datetime]::parseexact($invoice, 'dd-MMM-yy', $null).ToString('yyyy-MM-dd')

# Output
2020-09-02