HowTo_TestAddrEntryEmptyField

How can I test if a field is empty when using an adr file?

Tests on empty fields are simply tests on an empty argument. Unlike tests on specific contents, which are preferably performed with \Ifstr, the test on an empty field is therefore better performed with \IfArgIsEmpty. Both statements are provided by package scrbase and are therefore automatically available when using any KOMA-Script class.

Both statements can thus be used for personalized German serial letters, for example (the example is in German, because German gendering is much more complicated than in English):

\begin{filecontents}{\jobname.adr}
% {last name}{first name}{street}{zip code}{city}{gender}{}{abbreviation}
\addrentry{Muster}{}{Stra\ss e 1}{12345}{Hier}{}{}{}{TESTA}
\addrentry{Nachname}{Peter}{Stra\ss e 2}{54321}{Dort}{m}{}{}{TESTB}
\addrentry{}{Petra}{Stra\ss e 3}{98765}{Anderswo}{f}{}{}{TESTC}
\addrentry{}{}{Stra\ss e 1}{12345}{Hier}{}{}{}{TESTD}
\end{filecontents}

\documentclass{scrlttr2}

\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}

% Empfänger: #1 = Vorname, #2 = Nachname, #3 = Ersatzbezeichnung
\newcommand*{\IntelliName}[3]{%
  \IfArgIsEmpty{#1}{%
    \IfArgIsEmpty{#2}{#3}{ #2}%
  }{
    #1%
    \IfArgIsEmpty{#2}{}{\ #2}%
  }%
}

\renewcommand{\addrentry}[9]{%
  \begin{letter}{%
      \IntelliName{#2}{#1}{Bewohner:in}\\
      #3\\
      #4 #5%
    }
    \opening{Hallo\IntelliName{#2}{#1}{},}

    wir teilen Ihnen hiermit mit, dass das Haus demnächst
    mit einer Videoklingelanlage.
    Jede\Ifstr{#6}{m}{r Bewohner}{%
      \Ifstr{#6}{f}{ Bewohnerin}{ Person, die hier wohnt,}%
    }
    erhält einen eigenen Zugangscode für unsere geniale
    SmartPhone-App \texttt{WatchMeEveryWhery}.

    \closing{Mit freundlichen Grüßen}\
  \end{letter}
}

\setkomavar{subject}{Neue Klingelanlage}
\setkomavar{fromname}{Ausbeuter \& Co.}
\setkomavar{fromaddress}{Wir-kriegen-alle-Weg 666\\77777 Freibeuting}
\setkomavar{signature}{Ihre Hausverwaltung}
\let\raggedsignature\raggedright

\begin{document}
\input{\jobname.adr}
\end{document}

In the definition of \IntelliName, the \IfArgIsEmpty tests are used to ensure that meaningful addressing can take place regardless of whether the last name and first name fields in the adr file are actually assigned. If both the first name (argument 1) and the last name (argument 2) are empty, the replacement name from argument 3 is used.

With the nested \Ifstr test in the letter text, a gender-specific naming is ensured. For this purpose, the sixth argument of \addrentry is evaluated accordingly.