Basics of Writing Unix Man Pages

2022-11-24T00:00:00-05:00

On Unix-like systems, the documents that one views with the man command (known as “man pages”) are written in a markup language called “roff” (short for “run off”) that dates back to the pre-Unix days in the 1960’s. roff is technically a full-blown programming language with numerous features, but you only need to know a very small subset in order to produce most man pages. This article will describe that subset so that you can go on to write man pages for your own software.

Man pages, like most roff documents, use a roff macro package that defines a set of high-level commands. The macro package used by most man pages is, unsurprisingly, the man package, and that is what is covered here. Some man pages instead use the mdoc package, which originated in BSD. Modern versions of the man command use the mandoc package for processing man pages, which autodetects whether a file is written using man or mdoc and processes it accordingly.

Contents

roff Syntax
Document Structure Commands
Font Commands
Additional Escape Sequences
Man Page Conventions
Rendering a Man Page
A Sample Man Page
Further References

roff Syntax

A roff file is composed of a mixture of control lines — lines that start with a control character, usually a period or single-quote — and text lines — lines that do not.

Control lines are commands to roff (also known as requests). They consist of a control character & a command name followed by some number of space-separated (not tab-separated!) arguments. To include spaces in an argument, either escape them with a backslash or enclose the entire argument in double-quotes; to use double-quotes inside an argument, write them as \(dq.

For example, the input:

.B Bold
and brash?  More like
.IR Belongs " in the " Trash.

contains the command .B (for making text bold) with the argument “Bold” and the command .IR (for alternating between italic and roman text) with the arguments “Belongs” (which will be italic), “ in the ” (which will be roman), and “Trash” (which will be italic). This is all rendered as:

Bold and brash? More like Belongs in the Trash.

There may be any number of spaces & tabs (or none at all) between the control character and the command name, but the control character must be the first character in the line.
A line with just a period is ignored.

Text lines give the text that will be displayed. They can contain escape sequences, inline commands that start with backslashes.

Whitespace around escape sequences is significant and is not discarded. The syntax of an escape sequence allows roff to automatically determine where it ends; for example, escape sequences starting with \( are always followed by two more characters to complete the sequence, and so an escape sequence like \(em (em-dash) can be embedded in the middle of a word: foo\(embar becomes “foo—bar”.
To start a text line with a period, precede the period with either a backslash or the escape sequence \&.
To render a literal backslash in text, use the escape sequence \\\\, \e, or \(rs.

For example, the input from above can be rewritten using escape sequences like so:

\fBBold\fR and brash?  More like \fIBelongs\fR in the \fITrash.\fR

A comment consists of a backslash and double quote (\") and extends to the end of the line. A full-line comment can be formed by using the command .\".

A single logical line can be broken across multiple physical lines by placing a backslash at the end of each physical line.

Document Structure Commands

.TH title section [footer-middle] [footer-outside] [header-middle]

This must be the first non-comment command in a man page, and it must appear exactly once. It sets the page title (which is conventionally in all-caps) and section number for the man page (see “Manual Sections” below) to the given values, to be displayed in the form title(section) at the left & right sides of the header of the rendered manual page.

The remaining three arguments are optional. To omit an argument but still be able to specify an argument after it, write \& in place of the omitted argument.

If footer-middle is given, it will be rendered in the middle of the footer. This argument is usually set to the date the man page was written.
If footer-outside is given, it will be rendered on the left side of the footer. This is usually set to the version of the software being documented.
If header-middle is given, it will be rendered in the middle of the header. If it is omitted and section is a number from 1 to 9, certain versions of man will supply a default value.

.SH [name]

Start a section with the given name. If no argument is given, the next line will be used as the name.

.SS [name]

Start a subsection with the given name. If no argument is given, the next line will be used as the name.

.LP or .PP or .P

Paragraph break, resetting any indentation caused by the .TP, .IP, or .HP command

.TP [n]

Start a labelled, indented paragraph. The next text line after this command is the paragraph label, and any following text lines up to the next .PP will be indented. If a numeric argument is given, the paragraph will be indented by that many columns.

.IP [text] [n]

Start an indented paragraph. The text argument, if given, will be used as the paragraph’s bullet/“tag”; this is usually the bullet escape sequence (\(bu), the em-dash escape sequence (\(em), or a number followed by a period. If no text argument is supplied, no bullet will be present, but the following paragraph will still be indented; this can be used to start a new indented paragraph after an initial indented paragraph created by .TP, .IP, or .HP.

If a numeric second argument is given, the paragraph will be indented by that many columns.

.HP [n]

Start an indented paragraph in which the first line is not indented. If a numeric second argument is given, the paragraph will be indented by that many columns.

.RS [n]

Increase the amount of indentation until a corresponding .RE. If a numeric second argument is given, the indentation will be increased by that many columns.

.RE

Undo the increase in indentation caused by the last .RS

.br

Insert a line break

.sp

Skip a line

.sp N

Skip N lines

Font Commands

The following escape sequences can be used to change the font within a text line:

\fB: Change the font to bold
\fI: Change the font to italic (on a terminal, underlined)
\fR: Change the font to roman
\fP: Change back to the previous font

The following requests render an argument in a given font:

.B [text]: Renders the given text (or the text of the next line if no argument is given) in bold with a word break before & after.
.I [text]: Renders the given text (or the text of the next line if no argument is given) in italic (on a terminal, underlined) with a word break before & after.

The following commands take multiple arguments and render them in alternating fonts. A word break/whitespace will be inserted before & after the arguments, but there will be no words breaks/whitespace inserted between the arguments. For example, the following:

This is
.BI very styled
text.

will render as:

This is verystyled text.

.RB text ...: Renders the given arguments in alternating roman and bold, roman first.
.BR text ...: Renders the given arguments in alternating bold and roman, bold first.
.RI text ...: Renders the given arguments in alternating roman and italic/underlined, roman first.
.IR text ...: Renders the given arguments in alternating italic/underlined and roman, italic/underlined first.
.BI text ...: Renders the given arguments in alternating bold and italic/underlined, bold first.
.IB text ...: Renders the given arguments in alternating italic/underlined and bold, italic/underlined first.

Tip

While modern groff lets you use these commands with any number of arguments, traditional implementations limit usage to six arguments; keep this in mind if you want to make your man page portable.

Additional Escape Sequences

Select Non-ASCII Characters

See grof_char(7) for the complete set of available character escape sequences.

Escape	Character
`\(bu`	bullet (•)
`\*R`	registration symbol (®)
`\*(Tm`	trademark symbol (™)
`\(co`	copyright (©)
`\(em`	em-dash (—)
`\(en`	en-dash (–)
`\(rq`	right double-quote (“)
`\(lq`	left double-quote (”)
`\(oq`	left single-quote (‘)
`\(cq`	right single-quote (’)

Note

When viewing a man page in the terminal, not all installations will display Unicode characters. On systems that display man pages in ASCII (which include macOS as of Big Sur), non-ASCII characters will be rendered as the visually closest ASCII character where possible.

Special ASCII Characters

Some output devices transform certain ASCII input characters to similar Unicode characters, so the following escape sequences can be used to ensure that the desired ASCII character appears in the rendered man page:

Escape	Character
`\(aq`	Apostrophe (‘)
`\(ga`	Grave accent (`)
`\(ha`	Caret/circumflex accent (^)
`\(ti`	Tilde (~)
`\-`	Hyphen/minus (-)

Other

A backslash followed by a space produces a non-breaking space that remains at a fixed width when text is justified.
\~ produces a non-breaking space that nevertheless stretches like a normal inter-word space when justifying text.
\& produces a non-printable, zero-width character. It can be placed next to a token to deprive it of any special meaning; for example, it can be placed after a period at the end of an abbreviation to prevent it from being treated as the end of a sentence.

Man Page Conventions

Manual Sections

Each man page is traditionally placed into one of nine manual sections (not to be confused with the sections within a man page created by the .SH command; for that, see below). The pages for a given section are stored together, and the section number is also used as the file extension. The sections are:

Commands for use by general users
C system calls
C library functions, libraries, & headers
Devices, special files, and sockets
File formats
Games
Miscellaneous
Commands for use by system administrators (including servers/daemons)
C kernel functions

Sections of a Man Page

The contents of a man page are divided into sections by the .SH command. Different sources give slightly different lists of the “standard” sections, but the most common, in roughly the order they should appear in a man page, are:

NAME

Gives the name of the man page and a short description of what it documents. This is usually considered the only mandatory section.

In order for a man page named “foobar” to be properly indexed by whatis and apropos, NAME must be the first section in the man page, and the .SH NAME line must be followed immediately by a line of the form foobar \- short description of foobar.

SYNOPSIS

Shows the syntax for invoking a command or calling a C function.

The synopsis for a command usually follows the following conventions:

Text that should be entered as-is by the user (e.g., options and the name of the command) should be in bold, while placeholder text that should be replaced with some value by the user (e.g., command arguments) should be in italics/underlined.
Optional syntax elements (e.g., most options) should be enclosed in square brackets.
Alternative forms of a syntax element (e.g., the short and long form of an option) should be separated by whitespace and a vertical bar.
Syntax elements that can be repeated (e.g., arguments that can be given multiple times) are indicated by appending three periods (...).

See A Sample Man Page below for an example of these rules in action.

DESCRIPTION

An explanation of what the command, function, etc. does

OPTIONS

A list of any command-line options a program takes and their meanings. This list is usually created using .TP or .IP to produce paragraphs labeled with the option they describe, with each option in bold and any argument it may take in italics/underlined.

EXIT STATUS

A list of the possible exit statuses for a command and their meanings

ENVIRONMENT

A description of any environment variables that affect the command or function

FILES

A description of any files the command uses (configuration files, startup files, etc.). It is recommended that file paths be styled in italics/underlined.

NOTES

Any miscellaneous notes

BUGS

A list of known shortcomings in the documented software or functionality

EXAMPLES

Examples of how to use the software or functionality

AUTHORS

A list of the authors of the software and/or man page

REPORTING BUGS

Information on how to report any bugs found in the software

COPYRIGHT

SEE ALSO

A comma-separated list of related man pages and/or other documents. References to other man pages should be formatted with the name in bold and the section number in roman enclosed in parentheses.

Other Conventions

Use \- instead of plain - for ASCII hyphens, e.g., in command-line options. Use plain - in hyphenated words.
Blank lines are discouraged, as they may not render correctly in all output formats. Use the .sp command instead to produce a blank line, or use .PP to start a new paragraph.
Each sentence should typically start on a new line.
Use only a single space between words in text; multiple spaces will not be collapsed into one when rendering.

Rendering a Man Page

To render a man page in the terminal the way that man would, run man -l path/to/man/page. (On macOS, you have to instead run mandoc -a path/to/man/page). You may also want to pass the --warnings option (-Wall for mandoc) in order to catch any problematic syntax.

If your version of man does not support the -l option, you can instead run groff (GNU roff, the typical roff implementation on nearly all Unix machines nowadays) directly with groff -man -Tutf8 path/to/man/page | less -is.

Of course, groff can render to more than just terminals by changing the value passed to the -T option in the groff command. Values of interest include pdf, ps (for PostScript), and html; these require the gropdf, grops, and grohtml commands, respectively, to be installed in order to work.

A Sample Man Page

.TH FOOBAR 1 2022-11-24 v1.0
.SH NAME
foobar \- foo all your bars
.SH SYNOPSIS
.B foobar
[\fB\-a\fR \fIarg\fP]
.RB [ \-f | \-\-fu ]
.RB [ \-xyz ]
.IR "bar " ...
.SH DESCRIPTION
.B foobar
takes a list of one or more
.IR bar s
and foos each of them.
.PP
In detail, lorem ipsum dolor sit amet, consectetur adipisicing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi
ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore
eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non proident,
sunt in culpa qui officia deserunt mollit anim id est laborum.
.SH OPTIONS
.TP
.BI "\-a " arg
Put the apple at
.IR arg .
.TP
.BR \-f ", " \-\-fu
Do a FUBAR instead.
.IP
Note that this can permanently destroy your computer.
.IP \fB\-x\fR
Be exact about it.
.TP
.B -y
Be yucky about it.
.IP \fB-z\fR
Be zucchini about it.
.SH FILES
.TP
.I ~/.cache/foo
This is where the bars are stored.
.SH "SEE ALSO"
.BR man (1),
.BR groff (7),
.BR groff_man (7)
.PP
.I A Brief History of Foo
by Fabian Oscar Oh
.PP
.RI < https://www.example.com/foo/bar.html >

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Rendered:

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Further References

groff(7) man page: <https://man7.org/linux/man-pages/man7/groff.7.html>
groff_char(7) man page: <https://man7.org/linux/man-pages/man7/groff_char.7.html>
groff_man(7) man page: <https://man7.org/linux/man-pages/man7/groff_man.7.html>
man-pages(7) man page: <https://man7.org/linux/man-pages/man7/man-pages.7.html>

Knowledge Bits - groff

Basics of Writing Unix Man Pages