Source code for isdst.vbs

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Option Explicit
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Dim blnDST
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Dim dtmDate
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Dim strArg, strDate, strTimeZone
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dtmDate = Now
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If WScript.Arguments.Named.Count   > 0 Then Syntax

If WScript.Arguments.Unnamed.Count > 0 Then

	For Each strArg In WScript.Arguments.Unnamed

		strDate = Trim( strDate & " " & strArg )

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	Next
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	On Error Resume Next
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	If IsDate( strDate ) Then
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		dtmDate = CDate( strDate )
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	Else
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		Syntax
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	End If
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	On Error Goto 0
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End If
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blnDST = isDST( dtmDate )
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WScript.Echo "Date/time   : " & vbTab & dtmDate     & vbCrLf _

           & "Timezone    : " & vbTab & strTimeZone & vbCrLf _

           & "Date in DST : " & vbTab & blnDST

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If Not blnDST Then WScript.Quit 2
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Function isDST( myDate )
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' Returns TRUE if the specified date is in daylight Saving Time, or FALSE if not.

' The function ignores the 'ambiguous hour' right after the Standard Time transition.

	Dim myDay, myHour, myMinute, myMonth, myYear

	Dim lngDaylight, lngLocDate, lngStandard

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	Dim colItems, objItem, objWMIService
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	Dim strTZDST, strTZStd
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	' Parse the specified date/time
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	myDate   = CDate( myDate )
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	myDay    = DatePart( "d",    myDate )
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	myMonth  = DatePart( "m",    myDate )
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	myYear   = DatePart( "yyyy", myDate )
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	myHour   = DatePart( "h",    myDate )
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	myMinute = DatePart( "n",    myDate )
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```

	Set objWMIService = GetObject( "winmgmts://./root/cimv2" )

	Set colItems = objWMIService.ExecQuery( "SELECT * FROM Win32_TimeZone", , 48 )

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	For Each objItem in colItems
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		With objItem
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			' Convert the Daylight Start date/time, specified date/time and Standard Start date/time to long integers (YYYYMMDDHHmm)

			lngDaylight = .DaylightMinute + 100 * .DaylightHour + 10000 * LastDoW( .DaylightDayOfWeek, .DaylightMonth, myYear, .DaylightDay ) + 1000000 * .DaylightMonth + 100000000 * myYear

			lngLocDate  =  myMinute       + 100 *  myHour       + 10000 * myDay                                                               + 1000000 *  myMonth       + 100000000 * myYear

			lngStandard = .StandardMinute + 100 * .StandardHour + 10000 * LastDoW( .StandardDayOfWeek, .StandardMonth, myYear, .StandardDay ) + 1000000 * .StandardMonth + 100000000 * myYear

			' Store the names for DST and Standard Time

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			strTZDST    = .DaylightName
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			strTZStd    = .StandardName
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		End With
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	Next
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	Set colItems = Nothing
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	Set objWMIService = Nothing
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```

	' Now that we have the long integers for the date/times, the actual comparison is quite straightforward

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	If lngLocDate < lngDaylight Then
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		isDST       = False
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		strTimeZone = strTZStd
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	ElseIf lngLocDate >= lngStandard Then
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		isDST       = False
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		strTimeZone = strTZStd
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	Else
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		isDST       = True
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		strTimeZone = strTZDST
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	End If
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End Function
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```

Function LastDoW( myDoW, myMonth, myYear, myWoM )

' Returns the day of the month for the specified week day, month, year and week of month

' e.g. LastDoW( 0, 3, 2011, 5 ) will return the last (5) Sunday (0) of March (3) 2011, which is 27

```
	Dim i, j
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	j = 0
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	LastDoW = 0
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	For i = 1 To 31
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		If myWoM > j Then
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			If IsDate( myYear & "-" & myMonth & "-" & i ) Then

				If DatePart( "w", CDate( myYear & "-" & myMonth & "-" & i ), vbSunday ) = myDoW + 1 Then

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						j = j + 1
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						LastDoW = i
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				End If
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			End If
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		End If
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	Next
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End Function
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Sub Syntax
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	Dim strMsg
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	strMsg = vbCrLf _
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	       & "isDST.vbs,  Version 1.10" _
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	       & vbCrLf _
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	       & "Check if the current or specified date/time is in Daylight Saving Time" _

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	       & vbCrLf & vbCrLf _
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	       & "Usage:"  & vbTab & "ISDST.VBS  [ date  time ]" _

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	       & vbCrLf & vbCrLf _
```

	       & "Notes:" & vbTab & "Displays the result on screen, and returns 'errorlevel' 0 if the" _

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	       & vbCrLf _
```

	       & "      " & vbTab & "date is in DST, or 2 if not (1 is reserved for command line errors)." _

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	       & vbCrLf _
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	       & "      " & vbTab & "If no date/time is specified, the current date/time is assumed." _

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	       & vbCrLf _
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	       & "      " & vbTab & "DST is checked according to the timezone rules for the current" _

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	       & vbCrLf _
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	       & "      " & vbTab & "year, as found in the registry." _

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	       & vbCrLf _
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	       & "      " & vbTab & "The script ignores the 'ambiguous hour' right after the transition" _

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	       & vbCrLf _
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	       & "      " & vbTab & "to Standard Time." _

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	       & vbCrLf & vbCrLf _
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	       & "Written by Rob van der Woude" _

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	       & vbCrLf _
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	       & "http://www.robvanderwoude.com"

```
	WScript.Echo strMsg
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	WScript.Quit 1
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End Sub
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```