Insert relative date and time specifications?

How can I specify a relative date and let LaTeX insert the resulting absolute one?

For example like this:

\somedatecommand{next thursday}


Which should result in:

Thursday, 20.10.2011


Or:

20.10.2011


Great would be also babel support (e.g. for non-english documents).

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Please have a look at Date calculations and datetime and datenumber package conflict? – Yiannis Lazarides Oct 16 '11 at 16:35
I agree with @YiannisLazarides, this should be solvable using Date calculations, i.e. use the advdate package. – Martin Scharrer Oct 16 '11 at 16:37
@YiannisLazarides, @Martin Scharrer - I have checked out the documentation to advdate and datetime but I can't figure out how to solve this. Today + n days works great - but something like 'next thursday' is different, i.e. the output is the same until the next thursday ... :) – maxschlepzig Oct 16 '11 at 18:19
Feel free to develop the package. Get today's date from system, parse input to \somedatecommand get day offset and provide the new date in the format required. Repeat same for all languages in babel or use the special date and time formats provided. First part is not that difficult and possibly can fit into a post below. – Yiannis Lazarides Oct 16 '11 at 18:34

You could use the datetime package to format the dates and quoting form the package documentation:

As from version 2.42, the datetime package is now compatible with babel, however you must load the datetime package after the babel package.

The harder part is determining the date to print. This can be achieved using \AdvanceDate[n] macro from the advdate package to advance the date by a specified number of days. Then it is just a matter of determining how many days we need to advance to get to "next day-of-week".

To start from a day other than the current day one can use \SetDate[dd/mm/yyyy].

\documentclass{article}
\usepackage{xstring}% Needed for \IfStrEqCase
\usepackage{datenumber}% Date formatting
\usepackage{pgf}% For math
\usepackage[ddmmyyyy]{datetime}
\newdateformat{mydate}{\twodigit{\THEDAY}.\twodigit{\THEMONTH}.\THEYEAR}

\newcounter{dateOffset}%
\newcommand*{\SetDateOffsetForNext}[1]{%
\pgfmathsetcounter{dateOffset}{7-int(\the\value{datedayname})}% Initialize
\IfStrEqCase{#1}{%
{mon}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+1,7))}}%
{tue}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+2,7))}}%
{wed}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+3,7))}}%
{thu}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+4,7))}}%
{fri}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+5,7))}}%
{sat}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+6,7))}}%
{sun}{\pgfmathsetcounter{dateOffset}{int(mod(\the\value{dateOffset}+7,7))}}%
}[\PackageError{\SetDateOffsetForNext}{Do not know "#1" as day of week}{}]%
\IfEq{\the\value{dateOffset}}{0}{\pgfmathsetcounter{dateOffset}{7}}{}%
}%

\newcommand*{\PrintDateForNext}[1]{%
\SetDateOffsetForNext{#1}% Determine date offset
\mydate\today% Print specified date
is next #1\par% debug output
}

\begin{document}
\noindent
Working from current day:
Today is \mydate\today\par
\PrintDateForNext{mon}\par
\PrintDateForNext{tue}\par
\PrintDateForNext{wed}\par
\PrintDateForNext{thu}\par
\PrintDateForNext{fri}\par
\PrintDateForNext{sat}\par
\PrintDateForNext{sun}\par

\bigskip\noindent
Back to May the Fourth Be With You":
\SetDate[04/05/1977]% dd/mm/yyyy
Today is \mydate\today\par
\PrintDateForNext{mon}\par
\PrintDateForNext{tue}\par
\PrintDateForNext{wed}\par
\PrintDateForNext{thu}\par
\PrintDateForNext{fri}\par
\PrintDateForNext{sat}\par
\PrintDateForNext{sun}\par
\end{document}

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Awesome. I have to remember the \pgfmathsetcounter command. – maxschlepzig Oct 20 '11 at 8:27
@Peter Grill, I want to use this code, but I would like to change the date for today, I mean I would like to set '\setdate[02/01/2015]' and after that use '\PrintDateForNext{mon}'. How can I do it? – Gitano Jan 9 '15 at 5:45
@Gitano: You can use \SetDate[dd/mm/yyyy]. Have updated the solution to illustrate this. – Peter Grill Jan 9 '15 at 6:19
@PeterGrill, thanks, but there is a problem, 08.05.1977 is sunday. Now I understand why I had problems. Do you know why? – Gitano Jan 9 '15 at 6:39
@Gitano: Sorry don't know off hand. I'd suggest you post a separate question. Apologies for not testing it thoroughly. – Peter Grill Jan 9 '15 at 7:01