Bug in date command?

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Operating Systems Linux Bug in date command?
# 1  
Wrench Bug in date command?

Why is the result of this command off (or less) by one hour

date --date "1979-10-26 +54 hours" +%Y%m%d%H

The result is

It actually should be

It does it with adding minutes as well and only occurs on Oct. 26, from what I can tell. What's going on here?

Last edited by Scott; 08-06-2013 at 06:34 PM.. Reason: Please use code tags
# 2  
Spring forward, fall back.

When do the clocks change?

# 3  
Originally Posted by Scott
Spring forward, fall back.
Yep. In the UK and North America and a few other places, DST ended within the specified 54 hour interval: Daylight Saving Time Around the World 1979

# 4  
Quite interesting and esoteric.

How would you work around this?

---------- Post updated at 09:40 PM ---------- Previous update was at 09:18 PM ----------

Looking back at the results of the date command now (with the way I'm using it), I'm finding the answers to be off by +1 or -1 hr depending on the month (not just March and October). It may be a bigger problem.
# 5  
Originally Posted by hsemune
Quite interesting and esoteric.

How would you work around this?
What is there to work around? There is nothing wrong with the result. The only possible issue is that your date format is ambiguous because it does not include a timezone.

If you prefer to avoid daylight savings time, use UTC.

# 6  
Hi Alister,

Adding daylight savings time or any other time zones does not correct this issue. I still see the hour result being incremented by -1 or 1, whether it's in March, October, July, February, November. I'm still befuddled by this...


---------- Post updated at 09:47 AM ---------- Previous update was at 08:15 AM ----------

I wrote an if statement adding or subtracting an hour when I encounter this, so the problem is solved for me. But it's less than ideal that I have to write additional code to work around an important and widely used script function.
# 7  
I think the question has already been answered, but to reduce confusion, perhaps include the time zone %Z to see what is happening...
$ date --date "1979-10-26" '+%Y%m%d%H %Z'
1979102600 GMTDT

$ date --date "1979-10-26 +54 hours" '+%Y%m%d%H %Z'
1979102805 GMTST

$ date --utc --date "1979-10-26 +54 hours" '+%Y%m%d%H %Z'
1979102806 UTC


If you are still "befuddled", then that is to be expected. The first page of info date provides a quote...
File: coreutils.info,  Node: Date input formats

28 Date input formats

First, a quote:

     Our units of temporal measurement, from seconds on up to months,
     are so complicated, asymmetrical and disjunctive so as to make
     coherent mental reckoning in time all but impossible.  Indeed, had
     some tyrannical god contrived to enslave our minds to time, to
     make it all but impossible for us to escape subjection to sodden
     routines and unpleasant surprises, he could hardly have done
     better than handing down our present system.  It is like a set of
     trapezoidal building blocks, with no vertical or horizontal
     surfaces, like a language in which the simplest thought demands
     ornate constructions, useless particles and lengthy
     circumlocutions.  Unlike the more successful patterns of language
     and science, which enable us to face experience boldly or at least
     level-headedly, our system of temporal calculation silently and
     persistently encourages our terror of time.

     ...  It is as though architects had to measure length in feet,
     width in meters and height in ells; as though basic instruction
     manuals demanded a knowledge of five different languages.  It is
     no wonder then that we often look into our own immediate past or
     future, last Tuesday or a week from Sunday, with feelings of
     helpless confusion.  ...

     -- Robert Grudin, `Time and the Art of Living'.

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