Converts a Timestamp (Epochdate) into Datetime AND Converts a Datetime into a Unix Timestamp (Epochdate)

UnixTimeStampTools.ps1

function ConvertFrom-UnixTimeStamp
{
   <#
         .SYNOPSIS
         Converts a Timestamp (Epochdate) into Datetime

         .DESCRIPTION
         Converts a Timestamp (Epochdate) into Datetime

         .PARAMETER TimeStamp
         Timestamp (Epochdate)

         .PARAMETER Milliseconds
         Is the given Timestamp (Epochdate) in Miliseconds instead of Seconds?

         .EXAMPLE
         PS C:\> ConvertFrom-UnixTimeStamp -TimeStamp 1547839380

         Converts a Timestamp (Epochdate) into Datetime

         .EXAMPLE
         PS C:\> ConvertFrom-UnixTimeStamp -TimeStamp 1547839380712 -Milliseconds

         Converts a Timestamp (Epochdate) into Datetime, given value is in Milliseconds

         .NOTES
         Added the 'UniFi' (Alias for the switch 'Milliseconds') because the API returns miliseconds instead of seconds
   #>

   [CmdletBinding(ConfirmImpact = 'None')]
   [OutputType([datetime])]
   param
   (
      [Parameter(Mandatory,
            ValueFromPipeline,
            Position = 0,
      HelpMessage = 'Timestamp (Epochdate)')]
      [ValidateNotNullOrEmpty()]
      [Alias('Epochdate')]
      [long]
      $TimeStamp,
      [Parameter(ValueFromPipeline,
            ValueFromPipelineByPropertyName,
      Position = 1)]
      [Alias('UniFi')]
      [switch]
      $Milliseconds = $false
   )

   begin
   {
      # Set some defaults
      $UnixStartTime = '1/1/1970'

      # Cleanup
      $Result = $null
   }

   process
   {
      try
      {
         if ($Milliseconds)
         {
            $Result = ((Get-Date -Date $UnixStartTime -ErrorAction Stop -WarningAction SilentlyContinue).AddMilliseconds($TimeStamp))
         }
         else
         {
            try
            {
               $Result = ((Get-Date -Date $UnixStartTime -ErrorAction Stop -WarningAction SilentlyContinue).AddSeconds($TimeStamp))
            }
            catch
            {
               # Try a Fallback!
               $Result = ((Get-Date -Date $UnixStartTime -ErrorAction Stop -WarningAction SilentlyContinue).AddMilliseconds($TimeStamp))
            }
         }
      }
      catch
      {
         # get error record
         [Management.Automation.ErrorRecord]$e = $_

         # retrieve information about runtime error
         $info = [PSCustomObject]@{
            Exception = $e.Exception.Message
            Reason    = $e.CategoryInfo.Reason
            Target    = $e.CategoryInfo.TargetName
            Script    = $e.InvocationInfo.ScriptName
            Line      = $e.InvocationInfo.ScriptLineNumber
            Column    = $e.InvocationInfo.OffsetInLine
         }

         Write-Verbose -Message $info

         Write-Error -Message ($info.Exception) -ErrorAction Stop

         # Only here to catch a global ErrorAction overwrite
         break
      }
   }

   end
   {
      $Result
   }
}

function ConvertTo-UnixTimeStamp
{
   <#
         .SYNOPSIS
         Converts a Datetime into a Unix Timestamp (Epochdate)

         .DESCRIPTION
         Converts a Datetime into a Unix Timestamp (Epochdate)

         .PARAMETER Date
         The Date String that shoul be converted, default is now (if none is given)

         .PARAMETER Milliseconds
         Should the Timestamp (Epochdate) in Miliseconds instead of Seconds?

         .EXAMPLE
         PS C:\> ConvertTo-UnixTimeStamp

         Converts the actual time into a Unix Timestamp (Epochdate)

         .EXAMPLE
         PS C:\> ConvertTo-UnixTimeStamp -Milliseconds

         Converts the actual time into a Unix Timestamp (Epochdate), in milliseconds

         .EXAMPLE
         PS C:\> ConvertTo-UnixTimeStamp -Date ((Get-Date).AddDays(-1))

         Covert the same time yesterday into a Unix Timestamp (Epochdate)

         .EXAMPLE
         PS C:\> ConvertTo-UnixTimeStamp -Date ((Get-Date).AddDays(-1)) -Milliseconds

         Covert the same time yesterday into a Unix Timestamp (Epochdate), in milliseconds

         .NOTES
         Added the 'UniFi' (Alias for the switch 'Milliseconds') because the API returns miliseconds instead of seconds
   #>

   [CmdletBinding(ConfirmImpact = 'None')]
   [OutputType([long])]
   param
   (
      [Parameter(ValueFromPipeline,
            ValueFromPipelineByPropertyName,
      Position = 0)]
      [ValidateNotNullOrEmpty()]
      [Alias('TimeStamp', 'DateTimeStamp')]
      [datetime]
      $Date = (Get-Date),
      [Parameter(ValueFromPipeline,
            ValueFromPipelineByPropertyName,
      Position = 1)]
      [Alias('UniFi')]
      [switch]
      $Milliseconds = $false
   )

   begin
   {
      # Set some defaults
      $UnixStartTime = '1/1/1970'

      # Cleanup
      $Result = $null
   }

   process
   {
      try
      {
         if ($Milliseconds)
         {
            $Result = ([long]((New-TimeSpan -Start (Get-Date -Date $UnixStartTime -ErrorAction Stop -WarningAction SilentlyContinue) -End (Get-Date -Date $Date -ErrorAction Stop -WarningAction SilentlyContinue) -ErrorAction Stop -WarningAction SilentlyContinue).TotalMilliseconds))
         }
         else
         {
            $Result = ([long]((New-TimeSpan -Start (Get-Date -Date $UnixStartTime -ErrorAction Stop -WarningAction SilentlyContinue) -End (Get-Date -Date $Date -ErrorAction Stop -WarningAction SilentlyContinue) -ErrorAction Stop -WarningAction SilentlyContinue).TotalSeconds))
         }
      }
      catch
      {
         # get error record
         [Management.Automation.ErrorRecord]$e = $_

         # retrieve information about runtime error
         $info = [PSCustomObject]@{
            Exception = $e.Exception.Message
            Reason    = $e.CategoryInfo.Reason
            Target    = $e.CategoryInfo.TargetName
            Script    = $e.InvocationInfo.ScriptName
            Line      = $e.InvocationInfo.ScriptLineNumber
            Column    = $e.InvocationInfo.OffsetInLine
         }

         Write-Verbose -Message $info

         Write-Error -Message ($info.Exception) -ErrorAction Stop

         # Only here to catch a global ErrorAction overwrite
         break
      }
   }

   end
   {
      $Result
   }
}