There is a really nice package, lineno, which provides line-numbering and various options for customization, some of which I will discuss further below. The most common use is continuous line numbering throughout the document. The following two lines in the preamble will do the trick:
\usepackage{lineno}
\linenumbers
General lineno package example
Options
Some of the options the package provides include:
- [left]: Line numbers in left margin (default)
- [right]: Line numbers in right margin
- [switch]: Line number in outer margin (left for even, right for odd pages)
- [switch*]: Line numbers in inner margin
- [pagewise]: Restart numbering on every page
- [running]: Continuously number lines (default)
- [modulo]: Print only multiples of five
- [displaymath, mathlines]: Line numbers for math environments (both needed)
Example:
\usepackage[switch, modulo]{lineno}
\linenumbers
Line-numbers for a paragraph
The package provides a linenumbers environment to number a single paragraph.
\documentclass[11pt]{article}
\usepackage[english]{babel}
\usepackage{lineno, blindtext}
\begin{document}
\blindtext
\begin{linenumbers}
\blindtext
\end{linenumbers}
\blindtext
\end{document}
Paragraph line number example
If you do not leave an empty line between the previous and the actual paragraph, the previous may also get numbered.
Line numbers for math environments
We saw how math environments can be automatically wrapped for lines to be numbered. To number only a single set of equations, rather than the whole document, use the following code (from the lineno documentation):
\begin{linenomath*}
\begin{eqnarray}
b_1 &=& a_{11}x_1 + a_{12}x_2 \\
b_2 &=& a_{21}x_1 + a_{22}x_2
\end{eqnarray}
\end{linenomath*}
Numbering every other line
Instead of using the modulo option, it is possible to number every nth line (e.g. every second):
\usepackage{lineno}
\linenumbers
\modulolinenumbers[2]
Customizing numbers
The font of the numbers is readily changed by redefining linenumberfont. The default font style/size used is:
\renewcommand\linenumberfont{\normalfont\tiny\sffamily}
Since linenumber is just a counter, it is possible to change it to roman (roman/Roman) numbers or alphabetic characters (alph/Alph, max 26!):
\documentclass[11pt]{article}
\usepackage[english]{babel}
\usepackage{lineno, blindtext, color}
\linenumbers
\modulolinenumbers[2]
\renewcommand\thelinenumber{\color{red}\Roman{linenumber}}
\begin{document}
\blindtext
\end{document}
Customized line number example
Referencing line numbers
The package also implements labels/references to specific line numbers using linelabel/lineref. And by loading the hyperref package (always load last), clicking the references brings the user directly to the corresponding line.
\documentclass{article}
\usepackage{lineno, hyperref}
\linenumbers
\begin{document}
Some text.\linelabel{lne:label1}
\clearpage
See line \lineref{lne:label1}.
\end{document}
Documentation
Package documentation (user manual) for lineno.