Determine Daylight Savings status for different ti

Question

Is there a slick way in PowerShell to ascertain if a past date in another time zone is Daylight Savings or not? Here is the situation, our database is in Europe and the times and dates are local to that server. Since Europe and America start and stop DST at different times, i need to take into account the hour difference for those times. Thanks for your advice.

Answer 1

There is no need to try to determine whether DST is in effect or not. Just let the .NET Framework do the conversion for you.

First, decide which time zone IDs you are converting from and to.

You said your input time was in Europe, but you didn't specify exactly where. Like the US, Europe has multiple time zones. I'll assume you meant CET/CEST (UTC+1/+2). In Windows, you can use any of the following identifiers for this:

• "Central Europe Standard Time"
• "Central European Standard Time"
• "Romance Standard Time" (why? who knows.)
• "W. Europe Standard Time" (don't get fooled by the name, it's still central)

These are all the same (in Windows) except for their display names. If you want to be precise in which one you pick, refer to the CLDR reference.

For the US Central time zone, use "Central Standard Time".

Then just use the TimeZoneInfo.ConvertTimeBySystemTimeZoneId function, as follows:

# collect your input (through db, or whatever mechanism you have)
$inputDateTime = Get-Date -Date "2017-06-27 00:00:00"

# pick your time zones
$fromTimeZone = "Central Europe Standard Time"  # EU
$toTimeZone = "Central Standard Time"           # USA

# convert
$outputDateTime = [System.TimeZoneInfo]::ConvertTimeBySystemTimeZoneId(
  $inputDateTime, $fromTimeZone, $toTimeZone)

# output
Write-Output $outputDateTime