Calculating PowerShell ticks in Bash

Question

I am translating a PowerShell script in Bash.

This is how the ticks for current datetime are obtained in PowerShell:

[System.DateTime]::Now.Ticks;

By following the definition of Ticks , this is how I am trying to approximate the same calculation using the date command in bash:

echo $(($(($(date -u '+%s') - $(date -d "0001-01-01T00:00:00.0000000 UTC" '+%s'))) * 10000000 ))

This is what I got the last time I tried:

$ echo $(($(($(date -u '+%s') - $(date -d "0001-01-01T00:00:00.0000000 UTC" '+%s'))) * 10000000 )) ; pwsh -c "[System.DateTime]::Now.Ticks;"
637707117310000000
637707189324310740

In particular, the first 7 digits are identical, but digits in position 8 and 9 are still too different between the two values.

I calculated that this means there is just a 2 hours difference between the 2 values. But why? It cannot be the timezone, since I specified UTC timezone in both date commands, right? What do you think?

Note: my suspects about the timezone are increasing, since I am currently based in UTC+2 (therefore 2 hours difference from UTC), but how is this possible since I explicitly specified UTC as timezone in the date commands?

Answer 1

Solved it! The problem wasn't in the date commands, it was in the PowerShell command, which was using the +2 Timezone (CEST time). To fix this, I am now using UtcNow instead of Now .

This is what I am getting now:

$ echo $(($(($(date -u '+%s') - $(date -d "0001-01-01T00:00:00.0000000 UTC" '+%s'))) * 10000000 )) ; pwsh -c "[System.DateTime]::UtcNow.Ticks;"
637707132410000000
637707132415874110

As you can see, now all the digits are identical, except for the last 7th digits, since I added zeros on purpose to convert from seconds to ticks, as I am not interested in fractions of seconds (for now) and I consider them negligible.

Alternative way
Another way to make the two values identical (still excluding fractions of seconds), is to remove the -u option in the first date command in order to use the current time zone, and replace UTC with +0200 in the second date command. If I do this, I can leave Now on the PowerShell command (instead of replacing it with UtcNow ).

By doing this, I am getting:

$ echo $(($(($(date '+%s') - $(date -d "0001-01-01T00:00:00.0000000 +0200" '+%s'))) * 10000000)) ; pwsh -c "[System.DateTime]::Now.Ticks;"
637707218060000000
637707218067248090