Fancyhead Display Custom Shorten Version Of \leftmark

Question

Good day,

I would like to display a custom shorten version of the \leftmark with Fancyhdr.

Ideally it would be some type of switch with a case for each chapter.

Right now this is what the header's code looks like:

\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhead{}
\fancyfoot{}
\fancyhead[LO,RE]{\slshape \leftmark} % I would like to implement the string converter here

In pseudo-code it could be something like this:

var headerText = \leftmark
switch headerText:
  case "The very long chapter name":
    headerText = "The chapter name"
  case "Chapter two is also very long":
    headerText = "Chapter two"
  ...
\fancyhead[LO,RE]{\slshape headerText}

An important point in what I'm trying to do is that the output string could be totally different from the original.

Thank you in advance!

EDIT: I'm using Pandoc to convert a Markdown file into a PDF. So it would be nice to have a solution compatible with this method of generating books. Thank you!

Answer 1

Here is a solution that more or less implements your pseudo code. You can add this in the beginning of your converted LaTeX code (pandoc output).

Update: we have to be careful not to use this trick for chapters that put non-alphabetic characters in \leftmark or in their title. See below.

\documentclass{book}
\usepackage{fancyhdr}
\usepackage{lipsum}
\pagestyle{fancy}
\fancyhead{}
\fancyfoot{}
% Pseudo code:
% var headerText = \leftmark
% switch headerText:
%   case "The very long chapter name":
%     headerText = "The chapter name"
%   case "Chapter two is also very long":
%     headerText = "Chapter two"
%   ...
% \fancyhead[LO,RE]{\slshape headerText}
% Implementation:
\newcommand\chaptertitle[2]{\expandafter\def\csname=#1=\endcsname{#2}}
\newcommand\shorttitle[1]{\expandafter\csname=\leftmark=\endcsname}
\renewcommand{\chaptermark}[1]{\markboth{#1}{}}
\chaptertitle{One chapter with a very large chapter title}{Chapter One}
\chaptertitle{Another chapter title that really is much too long}{Chapter Two}
\fancyhead[LO,RE]{\slshape \shorttitle{\leftmark}} % I would like to implement the string converter here
                                % 
\begin{document}
\chapter{One chapter with a very large chapter title}
\lipsum
\chapter{Another chapter title that really is much too long}
\lipsum
\end{document}

This gives problems for chapters that use non-alphabetic characters in \markboth, for example \tableofcontents and similar ones. You can solve this by using the original header for these:

Update 2: The \newpage after \tableofcontents should be a \cleardoublepage (if documentclass book is used), otherwise there might be an empty page that still uses the bad \leftmark. Actually it is nicer to do a \newpage first, then change the header to be empty, then do a \cleardoublepage, and then change the header to its new form. In this case, if there is an empty page it will not have a header, which looks nicer. Such a page is always an even page, so we just change the header for even pages. So that is done with this update.

\renewcommand\contentsname{Index}
\fancyhead[RE]{\slshape \leftmark}
\tableofcontents
\newpage
\fancyhead[RE]{}
\cleardoublepage
\fancyhead[RE]{\slshape \shorttitle{\leftmark}}