Packages

How to Create Custom Commands in LaTeX

Custom commands (macros) let you avoid repetition and make your documents easier to maintain. Define a command once in the preamble and use it throughout your document—if you need to change it later, update it in one place.

Basic \newcommand

Define a simple command that expands to fixed text or formatting:

% In the preamble:
\newcommand{\eg}{e.g.,\@}
\newcommand{\ie}{i.e.,\@}
\newcommand{\R}{\mathbb{R}}

% In the document:
The set of real numbers is $\R$.
We observed several species, \eg cats and dogs.

Output: \R expands to the blackboard-bold R, and \eg produces 'e.g.' with correct spacing.

Commands with Arguments

Use [number] to specify how many arguments your command takes. Reference them with #1, #2, etc.:

% Command with 1 argument
\newcommand{\keyword}[1]{\textbf{\textit{#1}}}

% Command with 2 arguments
\newcommand{\highlight}[2]{\colorbox{#1}{\textcolor{white}{#2}}}

% Command with an optional argument (default value in [])
\newcommand{\note}[2][Note]{\textbf{#1:} #2}

% Usage:
\keyword{machine learning}
\highlight{blue}{Important}
\note{This is a default note.}
\note[Warning]{This is a warning.}

Output: keyword produces bold-italic text; highlight creates colored boxes; note has an optional label.

Renewing Existing Commands

Use \renewcommand to override an existing LaTeX command. Be careful—this changes behavior globally.

% Change how \emph behaves (default is italic)
\renewcommand{\emph}[1]{\textbf{#1}}

% Now \emph produces bold instead of italic:
This is \emph{emphasized} text.

% Override the abstract title
\renewcommand{\abstractname}{Executive Summary}

Output: \emph now renders bold text; the abstract section is titled 'Executive Summary'.

Custom Environments

Use \newenvironment to create reusable blocks with begin/end code:

% Define a custom environment
\newenvironment{important}
  {\begin{center}\bfseries\large}  % begin code
  {\end{center}}                     % end code

% More practical: a "note" box
\usepackage{tcolorbox}
\newenvironment{notebox}
  {\begin{tcolorbox}[colback=yellow!10, colframe=yellow!50!black, title=Note]}
  {\end{tcolorbox}}

% Usage:
\begin{important}
  This text is centered, bold, and large.
\end{important}

\begin{notebox}
  Remember to cite your sources.
\end{notebox}

Output: Custom environments produce styled blocks that you can reuse throughout the document.

💡 Tips

•Always define commands in the preamble (before \begin{document})
•Prefix personal commands with a unique letter to avoid conflicts (e.g., \myR instead of \R)
•Use \providecommand instead of \newcommand to define a command only if it doesn't already exist
•For complex macros with conditional logic, look into xparse and \NewDocumentCommand

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