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2019

  • in bash
  • 1 min read

Bash timezone checks

If you try to build an over-complicated scheduler using bash, you may run into issues when it comes to Daylight Saving Time. While it is a good idea to use Coordinated Universal Time (UTC), you might want to make sure you do not run into issues. The examples will use the date with the +"%H:%M" format.

Using date with the -u option: 

$ date -u +"%H:%M"
03:59

Using date after specifying the timezone with TZ= 

$ TZ="UTC" date +"%H:%M"
03:59

Here is a way to ensure you include the appropriate Daylight Saving Time and its dates of applicability. The example is from the 21.5.6 Specifying the Time Zone with TZ page.

In North American Eastern Standard Time (EST) and Eastern Daylight Time (EDT), the normal offset from UTC is 5 hours; since this is west of the prime meridian, the sign is positive. Summer time begins on March’s second Sunday at 2:00am, and ends on November’s first Sunday at 2:00am.

EST+5EDT

Here are some examples using date +"%H:%M" for timezones in the continental United States: 

$ TZ=":EST+5EDT" date +"%H:%M"
22:59
$ TZ=":CST+6CDT" date +"%H:%M"
21:59
$ TZ=":MST+7MDT" date +"%H:%M"
20:59
$ TZ=":PST+8PDT" date +"%H:%M"
19:59