etoolbox

Provides advanced programming tools and utilities for creating LaTeX classes and packages, with particular focus on e-TeX functionality.

Overview

Serves as a comprehensive toolkit for LaTeX developers and package authors, offering modern programming facilities and enhanced functionality beyond LaTeX's basic capabilities.

Implements convenient front-end interfaces to e-TeX primitives, making them more accessible to package developers.
Includes robust list processing functions, boolean switches, and hooks for document manipulation.
Offers efficient alternatives to traditional LaTeX programming constructs without modifying the core LaTeX kernel.
Particularly valuable for class and package authors developing sophisticated LaTeX extensions or customizations.
Commonly used in conjunction with other packages to implement advanced document formatting and automation features.

Getting Started

To use etoolbox, include it in your document preamble:

\documentclass{article}
\usepackage{etoolbox}

This package is primarily intended for package authors. The main functionality is:

% Example of a common etoolbox command
\appto\somecommand{additional content}

Examples

Using etoolbox to define and manipulate lists.

\documentclass{article}
\usepackage{etoolbox}

% Define a list
\newcommand{\mylist}{}
\begin{document}
\section{List manipulation with etoolbox}

% Add items to the list
\listadd{\mylist}{Apple}
\listadd{\mylist}{Banana}
\listadd{\mylist}{Cherry}

% Process the list
\noindent Items in my list:\par
\renewcommand*{\do}[1]{\textbullet\ #1\par}
\dolistloop{\mylist}

% Check if an item exists in the list
\noindent Checking list contents:\par
\ifinlist{Banana}{\mylist}{Banana is in the list.}{Banana is not in the list.}\par
\ifinlist{Orange}{\mylist}{Orange is in the list.}{Orange is not in the list.}
\end{document}

Using etoolbox's patching commands to modify existing commands.

\section{Original section}

% Let's patch the \section command to add stars before and after the title
\makeatletter
\pretocmd{\@sect}{\par\noindent Before patching: }{}{}
\apptocmd{\@sect}{\par\noindent After patching}{}{}
\makeatother

\section{Modified section}

Now let's make a more substantial modification to the section command:

% Create a completely patched version that adds stars around the title
\makeatletter
\patchcmd{\@sect}{#7}{$\star$ #7 $\star$}{}{}
\makeatother

\section{Starred section}

This section has stars around its title.

Using etoolbox's boolean facilities and conditional commands.

\documentclass{article}
\usepackage{etoolbox}

% Define some boolean flags
\newbool{draftmode}
\booltrue{draftmode}
\newbool{printimages}
\boolfalse{printimages}

\begin{document}
\section{Using boolean flags}

% Using boolean values to control document behavior
\ifbool{draftmode}
  {\textbf{Draft Mode:} This document is in draft mode.}
  {This document is in final mode.}

\par\bigskip

% Toggle a boolean
\notbool{printimages}{\booltrue{printimages}}{\boolfalse{printimages}}

% Check the toggled value
\ifbool{printimages}
  {Images will be printed.}
  {Images will not be printed.}

\par\bigskip

% Using numeric comparison
\newcommand{\score}{85}
\ifnumcomp{\score}{>}{70}
  {The score of \score\ is passing.}
  {The score of \score\ is failing.}

\par\bigskip

% Using string comparison
\newcommand{\status}{complete}
\ifstrequal{\status}{complete}
  {The project is complete.}
  {The project is still in progress.}
\end{document}