我想为客户创建发票scrlttr2。在此我通过设置文档日期\setkomavar{date}{\today}。
我重复使用这个日期日期自动将付款截止日期添加到信尾（截止日期 =今天的日期+未来 14 天）。
\today如果仅使用文档日期（参见 MWE），则这完全可以正常工作。
最小工作示例（MWE）：
\documentclass{scrlttr2}
\usepackage{advdate}
\setkomavar{date}{\today}
\begin{document}
Today is \today. Please pay until \AdvanceDate[14]\today.
\end{document}
但是，我还想使用自定义日期，例如 2018-05-05 作为单据日期。您知道如何根据任意日期而不是\today仅根据日期生成上述付款期限吗？
在最好的情况下，我可以将\today以及插入2018-05-05到-命令中\setkomavar{date}，因此以下示例应该将 14 天添加到我的自定义日期（使用自定义日期时）以及\today日期（如果用作\today文档日期）：
\documentclass{scrlttr2}
\usepackage{advdate}
\setkomavar{date}{2018-05-05}
\begin{document}
Today is \today. Please pay until \AdvanceDate[14]\date.
\end{document}
也许有用的软件包是：
答案1
首先，\today和变量的内容是有区别的date。设置变量date不会改变\today。请看以下示例：
\documentclass{scrlttr2}
\begin{document}
% default value of date variable is \today
Today is \today{} and the variable date stores \usekomavar{date}.
% changing value for variable date does not change \today!
\setkomavar{date}{2018-05-05}
Today is \today{} and the date variable stores \usekomavar{date}.
\end{document}
结果
该包advdate提供了附加命令\SaveDate，\SetDate和\DayAfter（参见包文档），可用于获取所需的结果。
首先，我们advdate在宏中将今天的日期保存为 dd/mm/yyyy（的所有宏都使用此语法）\invoicedate。
% Save dd/mm/yyyy for today
\newcommand*\invoicedate{}
\SaveDate[\invoicedate]
\invoicedate然后将用于自动设置 KOMA-Script 变量date和新变量paymentdate。您不必手动设置或更改这些变量！
\setkomavar{date}{{\SetDate[\invoicedate]\today}}
\newkomavar{paymentdate}
\setkomavar{paymentdate}{{\SetDate[\invoicedate]\DayAfter[14]}}
只有当你想为变量date（和依赖变量paymentdate）设置一个固定值时，你才需要使用以下宏\setinvoicedate。请注意，此宏会更改\invoicedate 和设置 KOMA-Scripts 变量date并paymentdate自动执行。因此您只需将此宏用于不同的发票/信函日期。
\newcommand*\setinvoicedate[1]{%
\ifstr{#1}{today}
{\SaveDate[\invoicedate]}%
{\renewcommand*\invoicedate{#1}}%
}
语法为\setinvoicedate{dd/mm/yyyy}。例如：
\setinvoicedate{24/12/2018}
您可以\setinvoicedate在一份文件中多次使用，例如，如果您的文件中有多张发票。如果您想将发票/信件日期重置为今天的日期，您可以使用
\setinvoicedate{today}
完整示例：
\documentclass{scrlttr2}
\usepackage{advdate}
% Save dd/mm/yyyy for today
\newcommand*\invoicedate{}
\SaveDate[\invoicedate]
\setkomavar{date}{{\SetDate[\invoicedate]\today}}
\newkomavar{paymentdate}
\setkomavar{paymentdate}{{\SetDate[\invoicedate]\DayAfter[14]}}
% should be possible to use a different invoicedate
\newcommand*\setinvoicedate[1]{%
\ifstr{#1}{today}
{\SaveDate[\invoicedate]}%
{\renewcommand*\invoicedate{#1}}%
}
% set a different invoice date
% syntax: \setinvoicedate{dd/mm/yyyy}
% if it should be reset to \today use \setinvoicedate{today}
\setinvoicedate{24/12/2018}
\newcommand\demo{% only for this example
\begin{itemize}
\item The invoice date is \usekomavar{date}.
\item Please pay until \usekomavar{paymentdate}.
\item But today is the \today.
\end{itemize}%
\bigskip
}
\begin{document}
\demo
\setinvoicedate{11/03/2019}%
Change the invoice date to \usekomavar{date}: \demo
\setinvoicedate{today}%
Reset the invoice date to today: \demo
\end{document}
或者使用课程选项numericaldate：
或者用包isodate来格式化日期输出：
代码：
\documentclass[english]{scrlttr2}
\usepackage{isodate}
\isodate
\usepackage{advdate}
% Save dd/mm/yyyy for today
\newcommand*\invoicedate{}
\SaveDate[\invoicedate]
% should be possible to use a different invoicedate
\newcommand*\setinvoicedate[1]{%
\ifstr{#1}{today}
{\SaveDate[\invoicedate]}%
{\renewcommand*\invoicedate{#1}}%
}
\setkomavar{date}{{\SetDate[\invoicedate]\today}}
\newkomavar{paymentdate}
\setkomavar{paymentdate}{{\SetDate[\invoicedate]\DayAfter[14]}}
% set a different invoice date
% syntax: \setinvoicedate{dd/mm/yyyy}
% if it should be reset to \today use \setinvoicedate{today}
\setinvoicedate{24/12/2018}
\newcommand\demo{% only for this example
\begin{itemize}
\item The invoice date is \usekomavar{date}.
\item Please pay until \usekomavar{paymentdate}.
\item But today is the \today.
\end{itemize}%
\bigskip
}
\begin{document}
\demo
\setinvoicedate{11/03/2019}%
Change the invoice date to \usekomavar{date}: \demo
\setinvoicedate{today}%
Reset the invoice date to today: \demo
\end{document}
更新关于以下评论：
为了避免周六或周日的付款日期，您可以加载包裹scrdate并使用
\setkomavar{paymentdate}{{%
\SetDate[\invoicedate]%
\ifnum\todaysnumber=6\DayAfter[16]% Saturday -> Monday
\else\ifnum\todaysnumber=0\DayAfter[15]% Sunday -> Monday
\else\DayAfter[14]
\fi\fi
}}
例子：
\documentclass{scrlttr2}
\usepackage{scrdate}% <- added
\usepackage{advdate}
% Save dd/mm/yyyy for today
\newcommand*\invoicedate{}
\SaveDate[\invoicedate]
\setkomavar{date}{{\SetDate[\invoicedate]\today}}
\newkomavar{paymentdate}
\setkomavar{paymentdate}{{% <- changed
\SetDate[\invoicedate]%
\ifnum\todaysnumber=6\DayAfter[16]% Saturday -> Monday
\else\ifnum\todaysnumber=0\DayAfter[15]% Sunday -> Monday
\else\DayAfter[14]
\fi\fi
}}
% should be possible to use a different invoicedate
\newcommand*\setinvoicedate[1]{%
\ifstr{#1}{today}
{\SaveDate[\invoicedate]}%
{\renewcommand*\invoicedate{#1}}%
}
% set a different invoice date
% syntax: \setinvoicedate{dd/mm/yyyy}
% if it should be reset to \today use \setinvoicedate{today}
\setinvoicedate{11/08/2018}
\newcommand\demo{% only for this example
\begin{itemize}
\item The invoice date is \usekomavar{date}.
\item Please pay until \usekomavar{paymentdate}.
\item But today is the \today.
\end{itemize}%
\bigskip
}
\begin{document}
\demo
\setinvoicedate{12/08/2019}%
Change the invoice date to \usekomavar{date}: \demo
\setinvoicedate{13/08/2018}%
Change the invoice date to \usekomavar{date}: \demo
\setinvoicedate{today}%
Reset the invoice date to today: \demo
\end{document}
答案2
datetime2这是一个基于的简单版本这个答案。请注意，使用 KOMA 变量日期并不像看起来那么容易，我为此引入了一个单独的命令（它被\edef编辑为允许\today作为值）。这将用于设置 KOMA 变量并进行计算。
\documentclass{scrlttr2}
% from https://tex.stackexchange.com/a/237129
\usepackage[calc,useregional]{datetime2}
\newcount\myct
\newcount\datecount
\newcommand{\myday}[2][0]{%
\DTMsavedate{mydate}{#2}%
\DTMsaveddateoffsettojulianday{mydate}{#1}{\myct}%
\DTMsavejulianday{mydate}{\number\myct}%
\DTMusedate{mydate}%
}
\edef\tmpdate{2018-05-05}
\setkomavar{date}{\tmpdate}
\begin{document}
Today is \today. Please pay until \myday[14]{2018-05-05}. This is still \today. \myday[14]{\tmpdate}
\end{document}