Re: date bug

[Eric Blake]

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According to Aganan, Nicholas on 4/23/2008 9:22 AM:
|
|    VERSION:  6.4

You might want to consider upgrading; the latest stable version is 6.11.

| root @ surplus# date 033100002008
|
| Mon Mar 31 00:00:00 EDT 2008
|
|
|
| [/usr/local/bin]
|
| root @ surplus# /usr/local/bin/date -d 'last month' '+%b'
|
| Mar
| <<<< BUG, should be Feb

Rather than changing your system clock, you can combine dates to test this
in one invocation:

$ date -d 'Mar 28, 2008 last month' +%b
Feb

Your example is not a bug.  'last month' is documented to be equivalent to
'alter only the month field, then renormalize'.  Starting from 'Mar 31'
and altering the month field yields 'Feb 31', but since that is not a read
date, the renormalization process settles on Mar 2 (this year, and Mar 3
on other years).

There are at least three viable means of handling this ambiguity - error
out if altering the month gives an ambiguous date, renormalizing, or
truncating; obviously, the method you wanted was not the method that
coreutils chose, but you can't call it a bug since it was ambiguous in the
first place.  No matter which way we pick, someone will complain that we
picked wrong.  The manual also suggests using unambiguous dates when
trying to switch just months, as in "date -d 'Mar 15, 2008 last month' +%b".

This is also an issue with ambiguous times that fall on daylight savings
boundaries.

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

Eric Blake             address@hidden
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