Suppose there is a file, f.

Is it possible to calculate every date (in YYYY-MM-DD format) that

a) falls between the last modification date of f and the current time, and
b) is a certain day of the week, say Wednesday or Saturday

in sh?

The idea is, I want to call a program with YYYY-MM-DD as parameter with
YYYY-MM-DD being every Saturday and Wednesday since the last time the
script was run.

In C, I'd probably start with the start date in seconds since the epoch,
check what day of week it is and add number of seconds till desired day of
week and then number of seconds in a week until we're in the future.

Can something like that be done in a shell script?

(preferably POSIX, but GNU should also be available on the target machine)

Thanks

--
Erwin Lindemann

On 2008-03-16, Erwin Lindemann wrote:
>
> Suppose there is a file, f.
>
> Is it possible to calculate every date (in YYYY-MM-DD format) that
>
> a) falls between the last modification date of f and the current time, and
> b) is a certain day of the week, say Wednesday or Saturday
>
> in sh?
>
> The idea is, I want to call a program with YYYY-MM-DD as parameter with
> YYYY-MM-DD being every Saturday and Wednesday since the last time the
> script was run.
>
> In C, I'd probably start with the start date in seconds since the epoch,

With GNU date, that is available using the %s specifier.

> check what day of week it is and add number of seconds till desired day of
> week and then number of seconds in a week until we're in the future.
>
> Can something like that be done in a shell script?
>
> (preferably POSIX, but GNU should also be available on the target machine)

Try the date arithmetic section of the FAQ:
<http://cfaj.freeshell.org/shell/cus-faq.html#6>

Also, Chapter 8 of my book, which is online at
<http://cfaj.freeshell.org/shell/ssr/08-The-Dating-Game.shtml>

--
Chris F.A. Johnson, author <http://cfaj.freeshell.org/shell/>
Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
===== My code in this post, if any, assumes the POSIX locale
===== and is released under the GNU General Public Licence

On Mar 15, 6:07 pm, Erwin Lindemann <elind...@wupp.invalid> wrote:
> Suppose there is a file, f.
>
> Is it possible to calculate every date (in YYYY-MM-DD format) that
>
> a) falls between the last modification date of f and the current time, and
> b) is a certain day of the week, say Wednesday or Saturday
>
> in sh?
>
> The idea is, I want to call a program with YYYY-MM-DD as parameter with
> YYYY-MM-DD being every Saturday and Wednesday since the last time the
> script was run.
>
> In C, I'd probably start with the start date in seconds since the epoch,
> check what day of week it is and add number of seconds till desired day of
> week and then number of seconds in a week until we're in the future.
>
> Can something like that be done in a shell script?
>
> (preferably POSIX, but GNU should also be available on the target machine)
>
> Thanks
>
> --
> Erwin Lindemann

ruby -rdate -e'p Date:AYNAMES[Date.parse($*[0]).wday]==
"Saturday"' 2008-03-15