Method to convert Windows time zones to IANA time zone database in PowerShell

I wasn’t able to find a good method for converting windows time zones to the IANA format I needed. This method isn’t perfect but it gets the job done for my purposes.

First you need to get the windowsZones.xml file from:
https://github.com/unicode-org/cldr/blob/main/common/supplemental/windowsZones.xml

The following PowerShell script converts the XML into the body of the switch statement used in the lookup script. This is based on another script I found here on StackOverflow.

# https://github.com/unicode-org/cldr/blob/main/common/supplemental/windowsZones.xml

# Download the xml file.
[Xml]$xml = Get-Content -Path "windowsZones.xml"

# Parse the fields we want from the XML.
$mappings1 = $xml.supplementalData.windowsZones.mapTimezones.mapZone | select Type,Other 

# Extrapolate extra rows for entries that contain more than one IANA name seperated by spaces.
# Example: |<mapZone other="Alaskan Standard Time" territory="US" type="America/Anchorage America/Juneau America/Nome America/Sitka America/Yakutat"/>
$mappings2 = $mappings1 | %{
    $mapping = $_
    $_.Type.Split(" ") | %{
        New-Object PSObject -Property @{type = $_; other = $mapping.other}
    }  
}

# Remove dup's
$mappings3 = $mappings2 | sort type -Unique

# Generate the case statements.
$mappings3 | %{ [String]::Format("`"{1}`" {{`"{0}`"}}", $_.Type, $_.Other)}

I need the switch to return only one entry so I pruned that list down. Here’s the lookup script:

$CurrentTimeZone = Get-TimeZone

$tz = Switch -Wildcard ($CurrentTimeZone.id)
{ 
  "Afghanistan Standard Time"       { "Asia/Kabul" }
  "Alaskan Standard Time"           { "America/Anchorage" }
  "Aleutian Standard Time"          { "America/Adak" }
  "Altai Standard Time"             { "Asia/Barnaul" }
  "Arab Standard Time"              { "Asia/Bahrain" }
  "Arabian Standard Time"           { "Asia/Dubai" }
  "Arabic Standard Time"            { "Asia/Baghdad" }
  "Argentina Standard Time"         { "America/Buenos_Aires" }
  "Astrakhan Standard Time"         { "Europe/Astrakhan" }
  "Atlantic Standard Time"          { "America/Halifax" }
  "Atlantic Standard Time"          { "Atlantic/Bermuda" }
  "AUS Central Standard Time"       { "Australia/Darwin" }
  "Aus Central W. Standard Time"    { "Australia/Eucla" }
  "AUS Eastern Standard Time"       { "Australia/Sydney" }
  "Azerbaijan Standard Time"        { "Asia/Baku" }
  "Azores Standard Time"            { "Atlantic/Azores" }
  "Bahia Standard Time"             { "America/Bahia" }
  "Bangladesh Standard Time"        { "Asia/Dhaka" }
  "Belarus Standard Time"           { "Europe/Minsk" }
  "Bougainville Standard Time"      { "Pacific/Bougainville" }
  "Canada Central Standard Time"    { "America/Regina" }
  "Cape Verde Standard Time"        { "Atlantic/Cape_Verde" }
  "Caucasus Standard Time"          { "Asia/Yerevan" }
  "Cen. Australia Standard Time"    { "Australia/Adelaide" }
  "Central America Standard Time"   { "America/Costa_Rica" }
  "Central Asia Standard Time"      { "Asia/Bishkek" }
  "Central Brazilian Standard Time" { "America/Cuiaba" }
  "Central Europe Standard Time"    { "Europe/Prague" }
  "Central European Standard Time"  { "Europe/Warsaw" }
  "Central Pacific Standard Time"   { "Pacific/Guadalcanal" }
  "Central Standard Time (Mexico)"  { "America/Mexico_City" }
  "Central Standard Time"           { "America/Chicago" }
  "Chatham Islands Standard Time"   { "Pacific/Chatham" }
  "China Standard Time"             { "Asia/Hong_Kong" }
  "Cuba Standard Time"              { "America/Havana" }
  "Dateline Standard Time"          { "Etc/GMT+12" }
  "E. Africa Standard Time"         { "Africa/Nairobi" }
  "E. Australia Standard Time"      { "Australia/Brisbane" }
  "E. Europe Standard Time"         { "Europe/Chisinau" }
  "E. South America Standard Time"  { "America/Sao_Paulo" }
  "Easter Island Standard Time"     { "Pacific/Easter" }
  "Eastern Standard Time (Mexico)"  { "America/Cancun" }
  "Eastern Standard Time"           { "America/New_York" }
  "Egypt Standard Time"             { "Africa/Cairo" }
  "Ekaterinburg Standard Time"      { "Asia/Yekaterinburg" }
  "Fiji Standard Time"              { "Pacific/Fiji" }
  "FLE Standard Time"               { "Europe/Helsinki" }
  "Georgian Standard Time"          { "Asia/Tbilisi" }
  "GMT Standard Time"               { "Europe/London" }
  "Greenland Standard Time"         { "America/Godthab" }
  "Greenwich Standard Time"         { "Atlantic/Reykjavik" }
  "GTB Standard Time"               { "Europe/Athens" }
  "Haiti Standard Time"             { "America/Port-au-Prince" }
  "Hawaiian Standard Time"          { "Pacific/Honolulu" }
  "India Standard Time"             { "Asia/Calcutta" }
  "Iran Standard Time"              { "Asia/Tehran" }
  "Israel Standard Time"            { "Asia/Jerusalem" }
  "Jordan Standard Time"            { "Asia/Amman" }
  "Kaliningrad Standard Time"       { "Europe/Kaliningrad" }
  "Korea Standard Time"             { "Asia/Seoul" }
  "Libya Standard Time"             { "Africa/Tripoli" }
  "Line Islands Standard Time"      { "Pacific/Kiritimati" }
  "Lord Howe Standard Time"         { "Australia/Lord_Howe" }
  "Magadan Standard Time"           { "Asia/Magadan" }
  "Magallanes Standard Time"        { "America/Punta_Arenas" }
  "Marquesas Standard Time"         { "Pacific/Marquesas" }
  "Mauritius Standard Time"         { "Indian/Mauritius" }
  "Middle East Standard Time"       { "Asia/Beirut" }
  "Montevideo Standard Time"        { "America/Montevideo" }
  "Morocco Standard Time"           { "Africa/Casablanca" }
  "Mountain Standard Time (Mexico)" { "America/Mazatlan" }
  "Mountain Standard Time"          { "America/Denver" }
  "Myanmar Standard Time"           { "Asia/Rangoon" }
  "N. Central Asia Standard Time"   { "Asia/Novosibirsk" }
  "Namibia Standard Time"           { "Africa/Windhoek" }
  "Nepal Standard Time"             { "Asia/Katmandu" }
  "New Zealand Standard Time"       { "Pacific/Auckland" }
  "Newfoundland Standard Time"      { "America/St_Johns" }
  "Norfolk Standard Time"           { "Pacific/Norfolk" }
  "North Asia East Standard Time"   { "Asia/Irkutsk" }
  "North Asia Standard Time"        { "Asia/Krasnoyarsk" }
  "North Korea Standard Time"       { "Asia/Pyongyang" }
  "Omsk Standard Time"              { "Asia/Omsk" }
  "Pacific SA Standard Time"        { "America/Santiago" }
  "Pacific Standard Time (Mexico)"  { "America/Tijuana" }
  "Pacific Standard Time"           { "America/Los_Angeles" }
  "Pakistan Standard Time"          { "Asia/Karachi" }
  "Paraguay Standard Time"          { "America/Asuncion" }
  "Qyzylorda Standard Time"         { "Asia/Qyzylorda" }
  "Romance Standard Time"           { "Europe/Brussels" }
  "Russia Time Zone 10"             { "Asia/Srednekolymsk" }
  "Russia Time Zone 11"             { "Asia/Anadyr" }
  "Russia Time Zone 3"              { "Europe/Samara" }
  "Russian Standard Time"           { "Europe/Moscow" }
  "SA Eastern Standard Time"        { "America/Recife" }
  "SA Pacific Standard Time"        { "America/Bogota" }
  "SA Western Standard Time"        { "America/Puerto_Rico" }
  "Saint Pierre Standard Time"      { "America/Miquelon" }
  "Sakhalin Standard Time"          { "Asia/Sakhalin" }
  "Samoa Standard Time"             { "Pacific/Apia" }
  "Sao Tome Standard Time"          { "Africa/Sao_Tome" }
  "Saratov Standard Time"           { "Europe/Saratov" }
  "SE Asia Standard Time"           { "Asia/Bangkok" }
  "Singapore Standard Time"         { "Asia/Singapore" }
  "South Africa Standard Time"      { "Africa/Johannesburg" }
  "South Sudan Standard Time"       { "Africa/Juba" }
  "Sri Lanka Standard Time"         { "Asia/Colombo" }
  "Sudan Standard Time"             { "Africa/Khartoum" }
  "Syria Standard Time"             { "Asia/Damascus" }
  "Taipei Standard Time"            { "Asia/Taipei" }
  "Tasmania Standard Time"          { "Australia/Hobart" }
  "Tocantins Standard Time"         { "America/Araguaina" }
  "Tokyo Standard Time"             { "Asia/Tokyo" }
  "Tomsk Standard Time"             { "Asia/Tomsk" }
  "Tonga Standard Time"             { "Pacific/Tongatapu" }
  "Transbaikal Standard Time"       { "Asia/Chita" }
  "Turkey Standard Time"            { "Europe/Istanbul" }
  "Turks And Caicos Standard Time"  { "America/Grand_Turk" }
  "Ulaanbaatar Standard Time"       { "Asia/Ulaanbaatar" }
  "US Eastern Standard Time"        { "America/Indianapolis" }
  "US Mountain Standard Time"       { "America/Phoenix" }
  "UTC"                             { "Etc/UTC" }
  "UTC+12"                          { "Pacific/Funafuti" }
  "UTC+13"                          { "Pacific/Enderbury" }
  "UTC-02"                          { "Atlantic/South_Georgia" }
  "UTC-08"                          { "Pacific/Pitcairn" }
  "UTC-09"                          { "Pacific/Gambier" }
  "UTC-11"                          { "Pacific/Midway" }
  "Venezuela Standard Time"         { "America/Caracas" }
  "Vladivostok Standard Time"       { "Asia/Vladivostok" }
  "Volgograd Standard Time"         { "Europe/Volgograd" }
  "W. Australia Standard Time"      { "Australia/Perth" }
  "W. Central Africa Standard Time" { "Africa/Algiers" }
  "W. Europe Standard Time"         { "Europe/Berlin" }
  "W. Mongolia Standard Time"       { "Asia/Hovd" }
  "West Asia Standard Time"         { "Asia/Almaty" }
  "West Bank Standard Time"         { "Asia/Hebron" }
  "West Pacific Standard Time"      { "Pacific/Guam" }
  "Yakutsk Standard Time"           { "Asia/Yakutsk" }
  "Yukon Standard Time"             { "America/Whitehorse" }
}

write-host $CurrentTimeZone
write-host $tz

You can simplify your code significantly by using XPath to lookup mappings directly against the XML document:

$xPath = '//supplementalData/windowsZones/mapTimezones/mapZone[@other = "Bahia Standard Time"]'
$bahiaEntry = $xml.SelectSingleNode($xPath)
$bahiaEntry.Type   # resolves to `America/Bahia`

Wrapping this in a function is trivial, but you may want to additionally host the function in a module, like so:

New-Module -Name tzResolutionModule -ScriptBlock {
  function Resolve-WindowsTimeZoneId {
    param(
      [Parameter(ValueFromPipeline, ValueFromPipelineByPropertyName)]
      [Alias('Id')]
      [string]$TZIdentifier = $(Get-TimeZone |% Id))

    process {
      $xPathExpression = '//supplementalData/windowsZones/mapTimezones/mapZone[@other = "{0}"]' -f $TZIdentifier
      $mapZoneEntry = $script:_timeZoneMap.SelectSingleNode($xPathExpression)

      if (-not $mapZoneEntry){
        throw "Unable to resolve time zone label '${TZIdentifier}'"
      }
      else {
        # we found at least one entry, output the first corresponding IANA identifier
        return -split $mapZoneEntry.Type |Select-Object -First 1
      }
    }
  }

  $_timeZoneMap = Invoke-RestMethod -Uri https://github.com/unicode-org/cldr/raw/main/common/supplemental/windowsZones.xml
} |Import-Module -Force

Wrapping the Resolve-WindowsTimeZoneId in a module allows us to take advantage of module-scoped variables for persistent storage – in this case to ensure we only download the zone mapping document once, on module import.

Now you can do:

PS ~> Resolve-WindowsTimeZoneId 'Central Standard Time'
America/Chicago

And get a near-instant response – but thanks to the [Parameter(...)] and [Alias(...)] decorators on the function parameter, you can now also do:

Get-TimeZone |Resolve-WindowsTimeZoneId
# or
'Central Standard Time' |Resolve-WindowsTimeZoneId

Filed under: Kiến thức lập trình - @ 11:49

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Method to convert Windows time zones to IANA time zone database in PowerShell