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Re: date bug (documentation bug?)

From: Eric Blake
Subject: Re: date bug (documentation bug?)
Date: Sat, 29 Apr 2006 16:12:51 -0600
User-agent: Thunderbird (Windows/20060308)

Hash: SHA1

According to stefano.sabatini-lala on 4/26/2006 10:25 AM:
> date doesn't work as expexcted after reading the man page.
> In order to set the date you need to do:
> $ date <date in some weird format>
> The command:
> $ date --set=<date in some weird format>
> doesn't appear to work.

Thanks for the report.  Actually, date without arguments is the only use
of the weird format.  When you use the --set option, you get the same date
parsing used by the --date option, which has an entire chapter devoted to
the various constructs parsed in the info manual (see 'info coreutils
date').  Unfortunately, the non-option format is so weird that --date (and
thus --set) do not reliably parse it; it looks too ambiguous and lacks
context to make it obvious what underlying format was intended.

> For example look at this session:
> address@hidden:~$ LANGUAGE=en_US sudo date 0426172006
> Qua Abr 26 17:20:00 WEST 2006
> address@hidden:~$ LANGUAGE=en_US sudo date --set=0426172006
> date: invalid date `0426172006'
> address@hidden:~$ LANGUAGE=en_US sudo  date --set="0426172006"
> date: invalid date `0426172006'
> The first command syntax (the only that actually work) isn't
> documented in the man page. 

Actually it is.  The date man page is auto-generated from 'date --help'
output, and as of the latest stable release of coreutils, 5.94, both
contain the synopsis of "date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]"

Try instead doing:
LANGUAGE=en_US sudo date --set='Qua Abr 26 17:20:00 WEST 2006'

If you then have a problem, then you have uncovered a bug in date; we
desire that we can unambiguously parse any output that date produces when
no format string was supplied.

> It's quite puzzling!

If you have any suggestions how the documentation could be made clearer,
or think you can patch the date parser to accept the weird format of date
as a valid argument to --date/--set, we would love to hear your ideas.

- --
Life is short - so eat dessert first!

Eric Blake             address@hidden
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