What is ‘include’ Command in LaTeX?

The \include command in LaTeX is used to import the contents of another LaTeX file into your current document. It’s a powerful tool for organizing and structuring large documents, especially for projects like books, theses, or reports. Here’s a guide on how to use the \include command in LaTeX.

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Basic Syntax

The basic syntax for the \include command is as follows.

\include{filename}

Replace filename with the actual filename of the file you want to include (without the .tex extension). It can be used anywhere within the document body (between \begin{document} and \end{document}).

Note:

The file extension (e.g., .tex) is optional with the \include command, as LaTeX assumes .tex by default. Therefore, you only need to provide the base filename.
Ensure that the file you want to include is in the same directory as your main LaTeX document, or provide the correct relative or absolute path to the file.

Function of ‘\include’

It includes the entire contents of another .tex file in your current document.
It is useful for modularizing your code, separating reusable sections, and organizing large projects.

Behavior of ‘\include’

Starts a new .aux file for the included file, used for cross-referencing.
Inserts a page break before the included content. In other words, the \include command always starts a new page before including the content. If you want to include content without starting a new page, consider using \input instead.
Only includes the content after the first \begin{document} in the included file.

Example

Assume you have a main LaTeX file named main.tex and two separate files, section1.tex and section2.tex, each containing the content for a specific section.

\documentclass{article}

\begin{document}

\title{My Document}
\author{John Doe}
\maketitle

\tableofcontents

\include{section1}
\include{section2}

\end{document}

Important Points

The \include command is often used for chapters in larger documents. Each included file is considered a separate unit, and LaTeX creates separate auxiliary files for each included file.
You can use the \includeonly command with a comma-separated list of file names in the preamble to selectively include certain files during compilation. It can be useful when working on large documents to speed up the compilation process. For example, \includeonly{filename1,filename2} will only include filename1 and filename2 during compilation.
Avoid cyclical includes (including a file that includes itself).