The TEX file (.tex)

The basics

What is a TEX file?

Anatomy

What's inside a TEX file

A LaTeX file has two parts: the preamble, which sets up the document, and the body between \begin{document} and \end{document}, which holds the content. Commands start with a backslash. Here is a short but complete file, part by part.

% notes.tex: compile with  pdflatex notes.tex
\documentclass[a4paper,11pt]{article}
\usepackage{amsmath}

\title{Notes}
\author{Ada Example}

\begin{document}
\maketitle

\section{Introduction}\label{sec:intro}
Text with \emph{emphasis} and maths: $E = mc^2$.
\begin{equation}
  \int_0^1 x^2 \, dx = \frac{1}{3}
\end{equation}
As Section~\ref{sec:intro} shows, \LaTeX{} numbers things for you.
\end{document}

1. 1% notes.tex: …

   A comment

   % hides the rest of the line from TeX. A literal percent sign has to be written \%.

2. 2\documentclass[a4paper,11pt]{article}

   The document class

   Always first. The class (article, report, book, beamer for slides, or a journal's own) decides the layout: page size, fonts, how headings look. Options go in square brackets, required arguments in braces.

3. 3\usepackage{amsmath}

   A package

   Adds features, here better maths environments. A real document often loads ten or twenty packages. Each must be installed in the TeX distribution, or compiling stops with File not found.

4. 4\title{Notes} \author{…}

   Document information

   Stored now, printed later by \maketitle. The class decides how the title block looks.

5. 5\begin{document}

   The start of the body

   Everything before it is the preamble, which may only set things up. Text before this line is an error.

6. 6\section{Introduction}\label{sec:intro}

   A numbered section with a label

   LaTeX numbers sections, equations, figures and tables itself. \label gives the number a name that \ref can use anywhere else in the document.

7. 7\emph{emphasis}

   Markup by meaning

   \emph says "emphasise this", and the class picks italics. This separation of content and appearance is the point of LaTeX.

8. 8$E = mc^2$

   Inline maths

   Dollar signs switch to maths mode, where letters become italic variables and ^ makes a superscript. Forgetting one is the source of the classic Missing $ inserted error.

9. 9\begin{equation} … \end{equation}

   A displayed equation

   Centred on its own line and numbered. \frac, \int and \, (a thin space) are maths commands.

10. 10Section~\ref{sec:intro}

    A cross-reference

    \ref prints the number of the label. The ~ is a space where the line may not break. On the first compile it prints ??, because numbers are only known at the end; the second run fills it in.

11. 11\end{document}

    The end

    Anything after this line is ignored, which is why some authors keep notes there.

Versions and variants

TeX vs LaTeX, and pdfTeX vs XeTeX vs LuaTeX

Tools

Distributions, editors and Overleaf

Under the hood

The build cycle and auxiliary files

$ pdflatex notes.tex      # run 1: writes labels to notes.aux, prints ?? for references
$ pdflatex notes.tex      # run 2: reads notes.aux, references are filled in
$ bibtex notes            # only with a .bib file: writes notes.bbl
$ pdflatex notes.tex      # run 3 (and 4): citations appear
$ latexmk -pdf notes.tex  # or let latexmk work out how many runs are needed

Troubleshooting

Common LaTeX errors and what they mean

How to

How to convert a TEX file to PDF, Word or HTML

Security

Is it safe to compile a TEX file?

Free downloads

Sample TEX files to download

Free sample TeX and LaTeX files, plus the PDFs they compile to, for testing editors, converters, compile services and previews. Every file compiles without errors or overfull boxes in TeX Live 2023.

Loading…

What's inside sample-article.tex

The file is commented: open it in a text editor and each numbered comment marks one of these parts. Compare it with sample-article.pdf, which is this file compiled.

1. Comments 1 to 3: class and preamble

   article on A4 at 11 pt, then geometry, amsmath, booktabs, tikz, microtype and hyperref, and the title, author and PDF metadata.

2. Comment 4: your own command

   \newcommand{\file}[1]{\texttt{#1}} defines \file{…}, used for file names throughout.

3. Comment 5: sections and labels

   Numbered sections with \label, referred to with \ref and cited with \cite.

4. Comment 6: maths

   Inline maths, a numbered equation and an align block lined up at &, referred to with \eqref.

5. Comment 7: a table

   A floating table with booktabs rules and a caption, comparing three engines.

6. Comment 8: a figure drawn in code

   A TikZ diagram of the build cycle: no image file, so it stays sharp at any zoom.

7. Comment 9: why two runs

   References and the page number in section 5 are only filled in on the second pdflatex run, from the .aux file.

8. Comment 10: the bibliography

   A thebibliography list with two entries, so no BibTeX run is needed.

All sample TEX files

• Commented LaTeX article

  sample-article.tex · 4.9 KB (5,057 bytes)

  Sections, maths, a table, a TikZ figure, cross-references and a bibliography, with ten numbered comments. Compiles with pdflatex (twice) using only standard packages.

  • Testing LaTeX compile services and editors
  • Teaching the parts of a LaTeX document
  DownloadOpen

• The article, compiled

  sample-article.pdf · 185.1 KB (189,571 bytes)

  Two A4 pages produced by pdfTeX from sample-article.tex, with embedded Type 1 fonts, PDF bookmarks and clickable references.

  • Comparing your own build with the expected output
  • Checking converters against a known result
  DownloadOpen

• Minimal plain TeX

  sample-plain.tex · 796 bytes

  Plain TeX without LaTeX: a font loaded by hand, text, inline and displayed maths, and \bye. Compile with pdftex (PDF) or tex (DVI).

  • Testing that a tool tells plain TeX from LaTeX
  • The smallest useful TeX document
  DownloadOpen

• UTF-8 with non-Latin scripts

  sample-unicode.tex · 2.2 KB (2,258 bytes)

  Accented Latin, Greek, Russian, Japanese, Arabic and Hebrew (right to left) with babel and system fonts (DejaVu, Noto Serif CJK). Needs XeLaTeX (or LuaLaTeX); pdfLaTeX stops with babel errors.

  • Checking encoding handling in editors and pipelines
  • Testing which engine a compile service uses
  DownloadOpen

• The UTF-8 file, compiled with XeLaTeX

  sample-unicode.pdf · 56.6 KB (57,983 bytes)

  One page from sample-unicode.tex, with the Arabic and Hebrew paragraphs set right to left and the fonts embedded.

  • Comparing font and script rendering
  • Checking text extraction from a multilingual PDF
  DownloadOpen

• Beamer slide deck

  sample-slides.tex · 1.7 KB (1,787 bytes)

  Three frames in the built-in Madrid theme at 16:9: a title slide, a list revealed step by step (\item<2->), and two columns with a table and a block. Compiles to five PDF pages with pdflatex.

  • Testing Beamer support in compile services
  • A starting point for LaTeX slides
  DownloadOpen

Ways to test with them

• Compile services: upload sample-article.tex and compare the result with sample-article.pdf. ?? in place of numbers means the service ran LaTeX only once.
• Engine detection: sample-unicode.tex compiles under XeLaTeX and stops under pdfLaTeX with This macro is available only in LuaLaTeX and XeLaTeX, so it shows at once which engine a service runs.
• Previews and syntax highlighting: open the .tex files in your viewer: comments, commands, maths and environments should be told apart.
• Conversion: run pandoc sample-article.tex -o out.docx or your converter and check which parts survive: headings, equations, the table, the TikZ figure.

Free to use for testing, teaching and demos, commercially or not, with no attribution needed. A link back to this page is always appreciated.

Questions

TEX files, frequently asked