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Name

groff - front end to the GNU roff document formatting system

Synopsis

Description

groff is the primary front end to the GNU roff document formatting system. GNU roff is a typesetting system that reads plain text input files that include formatting commands to produce output in PostScript, PDF, HTML, DVI, or other formats, or for display to a terminal. Formatting commands can be low-level typesetting primitives, macros from a supplied package, or user-defined macros. All three approaches can be combined. If no file operands are specified, or if file is “-”, groff reads the standard input stream.

A reimplementation and extension of the typesetter from AT&T Unix, groff is present on most POSIX systems owing to its long association with Unix manuals (including man pages). It and its predecessor are notable for their production of several best-selling software engineering texts. groff is capable of producing typographically sophisticated documents while consuming minimal system resources.

The groff command orchestrates the execution of preprocessors, the transformation of input documents into a device-independent page description language, and the production of output from that language.

Options

-h and --help display a usage message and exit.

Because groff is intended to subsume most users’ direct invocations of the troff(1) formatter, the two programs share a set of options. However, groff has some options that troff does not share, and others which groff interprets differently. At the same time, not all valid troff options can be given to groff.

groff-specific options
The following options either do not exist in GNU troff or are interpreted differently by groff.

--version

Write version information for groff and all programs run by it to the standard output stream; that is, the given command line is processed in the usual way, passing -v to the formatter and any pre- or postprocessors invoked.

Transparent options
The following options are passed as-is to the formatter program troff(1) and described in more detail in its man page.

-d name=string

Define string.

-m name

Process name.tmac before input files.

-o list

Output only pages in list.

-r cnumeric-expression
-r register=numeric-expression

Define register.

-w name
-W name

Enable (-w) or inhibit (-W) emission of warnings in category name.

Usage

The architecture of the GNU roff system follows that of other device-independent roff implementations, comprising preprocessors, macro packages, output drivers (or “postprocessors”), a suite of utilities, and the formatter troff at its heart. See roff(7) for a survey of how a roff system works.

The front end programs available in the GNU roff system make it easier to use than traditional roffs that required the construction of pipelines or use of temporary files to carry a source document from maintainable form to device-ready output. The discussion below summarizes the constituent parts of the GNU roff system. It complements roff(7) with groff-specific information.

Getting started
Those who prefer to learn by experimenting or are desirous of rapid feedback from the system may wish to start with a “Hello, world!” document.

$ echo "Hello, world!" | groff -Tascii | sed '/^$/d'
Hello, world!

We used a sed command only to eliminate the 65 blank lines that would otherwise flood the terminal screen. (roff systems were developed in the days of paper-based terminals with 66 lines to a page.)

Today’s users may prefer output to a UTF-8-capable terminal.

$ echo "Hello, world!" | groff -Tutf8 | sed '/^$/d'

Producing PDF, HTML, or TeX’s DVI is also straightforward. The hard part may be selecting a viewer program for the output.

$ echo "Hello, world!" | groff -Tpdf > hello.pdf
$ evince hello.pdf
$ echo "Hello, world!" | groff -Thtml > hello.html
$ firefox hello.html
$ echo "Hello, world!" | groff -Tdvi > hello.dvi
$ xdvi hello.html

Using groff as a REPL
Those with a programmer’s bent may be pleased to know that they can use groff in a read-evaluate-print loop (REPL). Doing so can be handy to verify one’s understanding of the formatter’s behavior and/or the syntax it accepts. Turning on all warnings with -ww can aid this goal.

$ groff -ww -Tutf8
\# This is a comment. Let's define a register.
.nr a 1
\# Do integer arithmetic with operators evaluated left-to-right.
.nr b \n[a]+5/2
\# Let's get the result on the standard error stream.
.tm \n[b]
3
\# Now we'll define a string.
.ds name Leslie\" This is another form of comment.
.nr b (\n[a] + (7/2))
\# Center the next two text input lines.
.ce 2
Hi, \*[name].
Your secret number is \n[b].
\# We will see that the division rounded toward zero.
It is
\# Here's an if-else control structure.
.ie (\n[b] % 2) odd.
.el even.
\# This trick sets the page length to the current vertical
\# position, so that blank lines don't spew when we're done.
.pl \n[nl]u
<Control-D>
Hi, Leslie.
Your secret number is 4.
It is even.

Paper format
In GNU roff, the page dimensions for the formatter troff and for output devices are handled separately. In the formatter, requests are used to set the page length (.pl), page offset (or left margin, .po), and line length (.ll). The right margin is not explicitly configured; the combination of page offset and line length provides the information necessary to derive it. The papersize macro package, automatically loaded by troff, provides an interface for configuring page dimensions by convenient names, like “letter” or “A4”; see groff_tmac(5). The formatter’s default in this installation is “A4”.

It is up to each macro package to respect the page dimensions configured in this way. Some offer alternative mechanisms.

For each output device, the size of the output medium can be set in its DESC file. Most output drivers also recognize a command-line option -p to override the default dimensions and an option -l to use landscape orientation. See groff_font(5) for a description of the papersize directive, which takes an argument of the same form as -p. The output driver’s man page, such as grops(1), may also be helpful. groff uses the command-line option -P to pass options to output devices; for example, use the following for PostScript output on A4 paper in landscape orientation.

groff -Tps -dpaper=a4l -P-pa4 -P-l -ms foo.ms > foo.ps

Front end
The groff program is a wrapper around the troff(1) program. It allows one to specify preprocessors via command-line options and automatically runs the appropriate postprocessor for the selected output device. Doing so, the manual construction of pipelines or management of temporary files required of users of traditional roff(7) systems can be avoided. Use the grog(1) program to infer an appropriate groff command line to format a document.

Language
Input to a roff system is in plain text interleaved with control lines and escape sequences. The combination constitutes a document in one of a family of languages we also call roff; see roff(7) for background. An overview of GNU roff language syntax and features, including lists of all supported escape sequences, requests, and predefined registers, can be found in groff(7). GNU roff extensions to the AT&T troff language, a common subset of roff dialects extant today, are detailed in groff_diff(7).

Preprocessors
A preprocessor interprets a domain-specific language that produces roff language output. Frequently, such input is confined to sections or regions of a roff input file (bracketed with macro calls specific to each preprocessor), which it replaces. Preprocessors therefore often interpret a subset of roff syntax along with their own language. GNU roff provides reimplementations of most preprocessors familiar to users of AT&T troff; these routinely have extended features and/or require GNU troff to format their output.

A preprocessor unique to GNU roff is preconv(1), which converts various input encodings to something GNU troff can understand. When used, it is run before any other preprocessors.

Most preprocessors enclose content between a pair of characteristic tokens. Such a token must occur at the beginning of an input line and use the dot control character. Spaces and tabs must not follow the control character or precede the end of the input line. Deviating from these rules defeats a token’s recognition by the preprocessor. Tokens are generally preserved in preprocessor output and interpreted as macro calls subsequently by troff. The ideal preprocessor is not yet available in groff.

Macro packages
Macro files are roff input files designed to produce no output themselves but instead ease the preparation of other roff documents. When a macro file is installed at a standard location and suitable for use by a general audience, it is termed a macro package.

Macro packages can be loaded prior to any roff input documents with the -m option. The GNU roff system implements most well-known macro packages for AT&T troff in a compatible way and extends them. These have one- or two-letter names arising from intense practices of naming economy in early Unix culture, a laconic approach that led to many of the packages being identified in general usage with the nroff and troff option letter used to invoke them, sometimes to punning effect, as with “man” (short for “manual”), and even with the option dash, as in the case of the s package, much better known as ms or even -ms.

Macro packages serve a variety of purposes. Some are “full-service” packages, adopting responsibility for page layout among other fundamental tasks, and defining their own lexicon of macros for document composition; each such package stands alone and a given document can use at most one.

mom HTML manual for extensive documentation. She—for mom takes the female pronoun—can be specified on the command line as -mom.

Others are supplemental. For instance, andoc is a wrapper package specific to GNU roff that recognizes whether a document uses man or mdoc format and loads the corresponding macro package. It can be specified on the command line as -mandoc. A man(1) librarian program may use this macro file to delegate loading of the correct macro package; it is thus unnecessary for man itself to scan the contents of a document to decide the issue.

Many macro files augment the function of the full-service packages, or of roff documents that do not employ such a package—the latter are sometimes characterized as “raw”. These auxiliary packages are described, along with details of macro file naming and placement, in groff_tmac(5).

Formatters
The formatter, the program that interprets roff language input, is troff(1). It provides the features of the AT&T troff and nroff programs as well as many extensions. The command-line option -C switches troff into compatibility mode, which tries to emulate AT&T troff as closely as is practical to enable the formatting of documents written for the older system.

A shell script, nroff(1), emulates the behavior of AT&T nroff. It attempts to correctly encode the output based on the locale, relieving the user of the need to specify an output device with the -T option and is therefore convenient for use with terminal output devices, described in the next subsection.

GNU troff generates output in a device-independent, but not device-agnostic, page description language detailed in groff_out(5).

Output devices
troff output is formatted for a particular output device, typically specified by the -T option to the formatter or a front end. If neither this option nor the GROFF_TYPESETTER environment variable is used, the default output device is ps. An output device may be any of the following.

Postprocessors
Any program that interprets the output of GNU troff is a postprocessor. The postprocessors provided by GNU roff are output drivers, which prepare a document for viewing or printing. Postprocessors for other purposes, such as page resequencing or statistical measurement of a document, are conceivable.

An output driver supports one or more output devices, each with its own device description file. A device determines its postprocessor with the postpro directive in its device description file; see groff_font(5). The -X option overrides this selection, causing gxditview to serve as the output driver.
grodvi(1)

provides dvi.