Getting the # of days difference between two dates in Powershell

Question

I am trying to get the number of days difference in Windows powershell, I am extracting the last date of the year i.e.. 20171231(yyyyMMdd) from a text file that I have locally stored the date in that file.

Here is the below code that I am trying but not able to get the difference of the days, am getting the wrong output by directly subtracting, if am converting the string extracted from the file and then subtract it with the date type, even then am getting the wrong output.

$DateStr = (Get-Date).ToString("yyyyMMdd")

$content = Get-Content C:\Users\Date.txt 

$diff = $content.ToString();

#Convert it to the date type
$diff = [datetime]::parseexact($diff, 'yyyyMMdd', $null)

#$diff3 = $diff - $DateStr

Answer 1

Use New-TimeSpan as it represents a time interval. Like so,

$d1 = '2017-01-01'
$d2 = '2017-05-01'
$ts = New-TimeSpan -Start $d1 -End $d2
$ts.Days # Check results
120

Answer 2

A quick, dirty, one line powershell script to get the difference between current date and any future date:

[math]::Ceiling((([DateTime]'mm-dd-yyyy')-(Get-Date)).TotalDays)

Answer 3

$DateStr is going to be a string, so it can't be parsed as a date. You can also use new-timespan to get the difference between two dates.

$Date = Get-Date

$diff = Get-Content C:\Users\Date.txt -raw

#Convert it to the date type
$diff = [datetime]::parseexact($diff, 'yyyyMMdd', $null)

$diff3 = New-TimeSpan -Start $diff -end $Date

#Number of days
$diff3.days