RE: date bug

[Aganan, Nicholas]

Normally we use '+%<param>' to get the desired information. Why don't we
use '-%<param> to denote the 'last or previous' value or maybe use
'+%-<param>'

Example:
  %-b   locale's abbreviated previous month name (e.g., Jan)
  %-B   locale's full previous month name (e.g., January)
  %-C   previous century; like %Y, except omit last two digits (e.g.,
21)
  %-m   previous month (01..12)
  %-W   previous week number of year, with Monday as first day of week
(00..53)
  %-y   last two digits of the previous year (00..99)
  %-Y   previous year


Sorry, I'm not a programmer, I'm only a SysAd (your end user :). I want
to help but can't do anything.

-----Original Message-----
From: Eric Blake [mailto:address@hidden 
Sent: Thursday, April 24, 2008 8:52 AM
To: Aganan, Nicholas; bug-coreutils
Subject: Re: date bug

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Please keep replies on the list, so that others may chime in.

According to Aganan, Nicholas on 4/24/2008 6:28 AM:
| You said "'last month' is documented to be equivalent to
| 'alter only the month field, then renormalize'" but your computation
is
| based on the date. 'last month' should provide the name of the
previous
| month with no dates.

You are looking at +%b in isolation.  But the code currently doesn't
work
that way.  When -d is encountered, the code computes a complete date,
orthogonal to the date components that are later requested by the +
format
string.  Therefore, "last month" on Mar 31 results in Feb 31, which must
be normalized, prior to even looking at what is to be output.

|
| If this month is Mar and you execute the 'last month' parameter the
| expected output should be Feb regardless what date it is.
|
| The best way to test this theory is by asking a person candidly "If
this
| month is March, what was last month?" or "What is today's month? What
| was last month?".
|
| If users want to get the date, I think the right parameter is '<num>
| days ago' or '<num> weeks ago'.

Then please propose a patch to improve date's behavior.  I think it
would
be reasonable to make the -d computation be a bit smarter about what
fields need to be normalized based on what fields will be output, but
the
task is not trivial, and I am not volunteering for the work.

|
| I found the workaround solution by using '31 days ago' if it is the
31st
| day of the month.

And that is what the manual recommends, too, since it does not result in
an ambiguous date that needs normalization.

|
| I will certainly move to 6.11.
|
| Thanks and more power.
|

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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