PowerShell: seconds since 1970?

A common date epoch is the 1st January 1970, or at least the number of seconds from this date. So if you want you convert the current date and time, or specified date and time to this epoch then knowing these commands may be useful. Recently I needed this to use with VMWare Workstation to configure a VM to always start at the same date and time. The VMX configuration option rtc.Startime can be set but requires the number of seconds since the epoch as it’s value.

Why PowerShell

Well this can be done in VBScript easily but I would have to write the script and run it. One advantage I have, if using Windows, is that PowerShell can be execute directly  at the prompt, so I can just type the code, no PS1 file required.  This is very much in the same way as I would with a Linux shell. PowerShell ships with Windows Vista, Server 2008, Windows 7 and Server 2008R2 can be downloaded and installed on other Windows Platforms.

Start PowerShell Prompt or ISE

Of course we need the PowerShell started so fire-up up your prompt or if you have the Graphical ISE.
PowerShell has a cmdlet called New-TimeSpan that takes two arguments (the first and second date). As you can see from below the code is not difficult. We pass the the epoch  time as the first argument and the current date and time as the second.

$EpochDiff = New-TimeSpan “01 January 1970 00:00:00” $(Get-Date)
write-host $EpochDiff.TotalSeconds

The only difficulty with this code is that it will result in the number of seconds and decimal places. We want the result to the nearest second.  PowerShell is very cool in the fact that if I user the Convert to Integer Function, [INT],  this will both convert to a whole number and round to the nearest whole number rather than failing if the source has decimal places. Look at the following code to improve our result.

$EpochDiff = New-TimeSpan “01 January 1970 00:00:00” $(Get-Date)
$EpochSecs = [INT] $EpochDiff.TotalSeconds
write-host $EpochSecs