Ubuntu Manpage: roff - concepts and history of roff typesetting

NAME

       roff - concepts and history of roff typesetting

DESCRIPTION

roff is the general name for a set of text formatting programs, known under names like
troff, nroff, ditroff, groff, etc. A roff system consists of an extensible text
formatting language and a set of programs for printing and converting to other text
formats. Unix-like operating systems distribute a roff system as a core package.

The most common roff system today is the free software implementation GNU roff, groff(1).
groff implements the look-and-feel and functionality of its ancestors, with many
extensions.

The ancestry of roff is described in section HISTORY. In this document, the term roff
always refers to the general class of roff programs, not to the roff command provided in
early UNIX systems.

In spite of its age, roff is in wide use today, for example, the manual pages on UNIX
systems (man pages), many software books, system documentation, standards, and corporate
documents are written in roff. The roff output for text devices is still unmatched, and
its graphical output has the same quality as other free type-setting programs and is
better than some of the commercial systems.

roff is used to format UNIX manual pages, (or man pages), the standard documentation
system on many UNIX-derived operating systems.

This document describes the history of the development of the roff system; some usage
aspects common to all roff versions, details on the roff pipeline, which is usually hidden
behind front-ends like groff(1); a general overview of the formatting language; some tips
for editing roff files; and many pointers to further readings.

HISTORY

Document formatting by computer dates back to the 1960s. The roff system itself is
intimately connected to the Unix operating system, but its roots go back to the earlier
operating systems CTSS and Multics.

The Predecessor RUNOFF
roff's ancestor RUNOFF was written in the MAD language by Jerry Saltzer for the Compatible
Time Sharing System (CTSS), a project of the Massachusetts Institute of Technology (MIT),
in 1963 and 1964 – note that CTSS commands were all uppercase.

In 1965, MIT's Project MAC teamed with Bell Telephone Laboratories (BTL) and General
Electric to begin the Multics system ⟨http://www.multicians.org⟩. A command called runoff
was written for Multics in the late 60s in the BCPL language, by Bob Morris, Doug McIlroy,
and other members of the Multics team.

Like its CTSS ancestor, Multics runoff formatted an input file consisting of text and
command lines; commands began with a period and were two letters. Output from these
commands was to terminal devices such as IBM Selectric terminals. Multics runoff had
additional features added, such as the ability to do two-pass formatting; it became the
main format for Multics documentation and text processing.

BCPL and runoff were ported to the GCOS system at Bell Labs when BTL left the development
of Multics.

The Classical nroff/troff System
At BTL, there was a need to drive the Graphic Systems CAT typesetter, a graphical output
device from a PDP-11 computer running Unix. As runoff was too limited for this task it
was further developed into a more powerful text formatting system by Joseph F. Ossanna,
who already programmed several runoff ports.

The name runoff was shortened to roff. The greatly enlarged language of Ossanna's version
already included all elements of a full roff system. All modern roff systems try to
implement compatibility to this system. So Joe Ossanna can be called the father of all
roff systems.

This first roff system had three formatter programs.

troff (typesetter roff) generated a graphical output for the CAT typesetter as its only
device.

nroff produced text output suitable for terminals and line printers.

roff was the reimplementation of the former runoff program with its limited features;
this program was abandoned in later versions. Today, the name roff is used to
refer to a troff/nroff system as a whole.

Ossanna's first version was written in the PDP-11 assembly language and released in 1973.
Brian Kernighan joined the roff development by rewriting it in the C programming language.
The C version was released in 1975.

The syntax of the formatting language of the nroff/troff programs was documented in the
famous Troff User's Manual [CSTR #54], first published in 1976, with further revisions up
to 1992 by Brian Kernighan. This document is the specification of the classical troff.
All later roff systems tried to establish compatibility with this specification.

After Ossanna's death in 1977, Kernighan went on with developing troff. In the late
1970s, Kernighan equipped troff with a general interface to support more devices, the
intermediate output format, and the postprocessor system. This completed the structure of
a roff system as it is still in use today; see section USING ROFF. In 1979, these
novelties were described in the paper [CSTR #97]. This new troff version is the basis for
all existing newer troff systems, including groff. On some systems, this device
independent troff got a binary of its own, called ditroff(7). All modern troff programs
already provide the full ditroff capabilities automatically.

Availability
The source code of both the ancient Unix and classical troff weren't available for two
decades. Meanwhile, it is accessible again (on-line) for non-commercial use, cf. section
SEE ALSO.

Free roff
The most important free roff project was the GNU implementation of troff, written from
scratch by James Clark and put under the GNU Public License ⟨http://www.gnu.org/copyleft⟩.
It was called groff (GNU roff). See groff(1) for an overview.

The groff system is still actively developed. It is compatible to the classical troff,
but many extensions were added. It is the first roff system that is available on almost
all operating systems – and it is free. This makes groff the de-facto roff standard
today.

An alternative is Gunnar Ritter's Heirloom Documentation Tools ⟨http://heirloom.sf.net⟩
project, started in 2005, which provides enhanced versions of the various roff tools found
in the OpenSolaris and Plan 9 operating systems, now available under free licenses.

USING ROFF

Most people won't even notice that they are actually using roff. When you read a system
manual page (man page) roff is working in the background. roff documents can be viewed
with a native viewer called xditview(1x), a standard program of the X window distribution,
see X(7x). But using roff explicitly isn't difficult either.

Some roff implementations provide wrapper programs that make it easy to use the roff
system on the shell command line. For example, the GNU roff implementation groff(1)
provides command line options to avoid the long command pipes of classical troff; a
program grog(1) tries to guess from the document which arguments should be used for a run
of groff; people who do not like specifying command line options should try the groffer(1)
program for graphically displaying groff files and man pages.

The roff Pipe
Each roff system consists of preprocessors, roff formatter programs, and a set of device
postprocessors. This concept makes heavy use of the piping mechanism, that is, a series
of programs is called one after the other, where the output of each program in the queue
is taken as the input for the next program.

The preprocessors generate roff code that is fed into a roff formatter (e.g. troff), which
in turn generates intermediate output that is fed into a device postprocessor program for
printing or final output.

All of these parts use programming languages of their own; each language is totally
unrelated to the other parts. Moreover, roff macro packages that were tailored for
special purposes can be included.

Most roff documents use the macros of some package, intermixed with code for one or more
preprocessors, spiced with some elements from the plain roff language. The full power of
the roff formatting language is seldom needed by users; only programmers of macro packages
need to know about the gory details.

Preprocessors
A roff preprocessor is any program that generates output that syntactically obeys the
rules of the roff formatting language. Each preprocessor defines a language of its own
that is translated into roff code when run through the preprocessor program. Parts
written in these languages may be included within a roff document; they are identified by
special roff requests or macros. Each document that is enhanced by preprocessor code must
be run through all corresponding preprocessors before it is fed into the actual roff
formatter program, for the formatter just ignores all alien code. The preprocessor
programs extract and transform only the document parts that are determined for them.

There are a lot of free and commercial roff preprocessors. Some of them aren't available
on each system, but there is a small set of preprocessors that are considered as an
integral part of each roff system. The classical preprocessors are

tbl for tables.
eqn for mathematical formulæ.
pic for drawing diagrams.
refer for bibliographic references.
soelim for including macro files from standard locations.
chem for drawing chemical formulæ.

Other known preprocessors that are not available on all systems include

grap for constructing graphical elements.
grn for including gremlin(1) pictures.

Formatter Programs
A roff formatter is a program that parses documents written in the roff formatting
language or uses some of the roff macro packages. It generates intermediate output, which
is intended to be fed into a single device postprocessor that must be specified by a
command-line option to the formatter program. The documents must have been run through
all necessary preprocessors before.

The output produced by a roff formatter is represented in yet another language, the
intermediate output format or troff output. This language was first specified in
[CSTR #97]; its GNU extension is documented in groff_out(5). The intermediate output
language is a kind of assembly language compared to the high-level roff language. The
generated intermediate output is optimized for a special device, but the language is the
same for every device.

The roff formatter is the heart of the roff system. The traditional roff had two
formatters, nroff for text devices and troff for graphical devices.

Often, the name troff is used as a general term to refer to both formatters.

Devices and Postprocessors
Devices are hardware interfaces like printers, text or graphical terminals, etc., or
software interfaces such as a conversion into a different text or graphical format.

A roff postprocessor is a program that transforms troff output into a form suitable for a
special device. The roff postprocessors are like device drivers for the output target.

For each device there is a postprocessor program that fits the device optimally. The
postprocessor parses the generated intermediate output and generates device-specific code
that is sent directly to the device.

The names of the devices and the postprocessor programs are not fixed because they greatly
depend on the software and hardware abilities of the actual computer. For example, the
classical devices mentioned in [CSTR #54] have greatly changed since the classical times.
The old hardware doesn't exist any longer and the old graphical conversions were quite
imprecise when compared to their modern counterparts.

For example, the Postscript device post in classical troff had a resolution of 720 units
per inch, while groff's ps device has 72000, a refinement of factor 100.

Today the operating systems provide device drivers for most printer-like hardware, so it
isn't necessary to write a special hardware postprocessor for each printer.

ROFF PROGRAMMING

Documents using roff are normal text files decorated by roff formatting elements. The
roff formatting language is quite powerful; it is almost a full programming language and
provides elements to enlarge the language. With these, it became possible to develop
macro packages that are tailored for special applications. Such macro packages are much
handier than plain roff. So most people will choose a macro package without worrying
about the internals of the roff language.

Macro Packages
Macro packages are collections of macros that are suitable to format a special kind of
documents in a convenient way. This greatly eases the usage of roff. The macro
definitions of a package are kept in a file called name.tmac (classically tmac.name). All
tmac files are stored in one or more directories at standardized positions. Details on
the naming of macro packages and their placement is found in groff_tmac(5).

A macro package that is to be used in a document can be announced to the formatter by the
command line option -m, see troff(1), or it can be specified within a document using the
file inclusion requests of the roff language, see groff(7).

Famous classical macro packages are man for traditional man pages, mdoc for BSD-style
manual pages; the macro sets for books, articles, and letters are me (probably from the
first name of its creator Eric Allman), ms (from Manuscript Macros), and mm (from
Memorandum Macros).

The roff Formatting Language
The classical roff formatting language is documented in the Troff User's Manual
[CSTR #54]. The roff language is a full programming language providing requests,
definition of macros, escape sequences, string variables, number or size registers, and
flow controls.

Requests are the predefined basic formatting commands similar to the commands at the shell
prompt. The user can define request-like elements using predefined roff elements. These
are then called macros. A document writer will not note any difference in usage for
requests or macros; both are written on a line on their own starting with a dot.

Escape sequences are roff elements starting with a backslash `\'. They can be inserted
anywhere, also in the midst of text in a line. They are used to implement various
features, including the insertion of non-ASCII characters with \(, font changes with \f,
in-line comments with \", the escaping of special control characters like \\, and many
other features.

Strings are variables that can store a string. A string is stored by the .ds request.
The stored string can be retrieved later by the \* escape sequence.

Registers store numbers and sizes. A register can be set with the request .nr and its
value can be retrieved by the escape sequence \n.

FILE NAME EXTENSIONS

       Manual  pages  (man  pages)  take  the  section number as a file name extension, e.g., the
       filename for this document is roff.7, i.e., it is kept in section 7 of the man pages.

       The classical macro packages take the package name as an extension,  e.g.  file.me  for  a
       document  using  the  me  macro  package, file.mm for mm, file.ms for ms, file.pic for pic
       files, etc.

       But there is no general naming scheme for roff documents, though file.tr for troff file is
       seen now and then.  Maybe there should be a standardization for the filename extensions of
       roff files.

       File name extensions can be very handy in conjunction with the less(1) pager.  It provides
       the  possibility to feed all input into a command-line pipe that is specified in the shell
       environment variable LESSOPEN.  This process is not well documented, so here an example:

              LESSOPEN='|lesspipe %s'

       where lesspipe is either a system supplied command or a shell script of your own.

EDITING ROFF

The best program for editing a roff document is Emacs (or Xemacs), see emacs(1). It
provides an nroff mode that is suitable for all kinds of roff dialects. This mode can be
activated by the following methods.

When editing a file within Emacs the mode can be changed by typing `M-x nroff-mode', where
M-x means to hold down the Meta key (or Alt) and hitting the x key at the same time.

But it is also possible to have the mode automatically selected when the file is loaded
into the editor.

• The most general method is to include the following 3 comment lines at the end of
the file.

.\" Local Variables:
.\" mode: nroff
.\" End:

• There is a set of file name extensions, e.g. the man pages that trigger the
automatic activation of the nroff mode.

• Theoretically, it is possible to write the sequence

.\" -*- nroff -*-

as the first line of a file to have it started in nroff mode when loaded.
Unfortunately, some applications such as the man program are confused by this; so
this is deprecated.

All roff formatters provide automated line breaks and horizontal and vertical spacing. In
order to not disturb this, the following tips can be helpful.

• Never include empty or blank lines in a roff document. Instead, use the empty
request (a line consisting of a dot only) or a line comment .\" if a structuring
element is needed.

• Never start a line with whitespace because this can lead to unexpected behavior.
Indented paragraphs can be constructed in a controlled way by roff requests.

• Start each sentence on a line of its own, for the spacing after a dot is handled
differently depending on whether it terminates an abbreviation or a sentence. To
distinguish both cases, do a line break after each sentence.

• To additionally use the auto-fill mode in Emacs, it is best to insert an empty roff
request (a line consisting of a dot only) after each sentence.

The following example shows how optimal roff editing could look.

This is an example for a
.I roff
document.
.
This is the next sentence in the same paragraph.
.
This is a longer sentence stretching over several
lines; abbreviations like `cf.' are easily
identified because the dot is not followed by a
line break.
.
In the output, this will still go to the same
paragraph.

Besides Emacs, some other editors provide nroff style files too, e.g. vim(1), an extension
of the vi(1) program.

AUTHORS

       Copyright (C) 2000,  2001,  2002,  2003,  2004,  2006,  2007,  2008,  2009  Free  Software
       Foundation, Inc.

       This  document  is distributed under the terms of the FDL (GNU Free Documentation License)
       version 1.3 or later.  You should have received a copy of the FDL on your  system,  it  is
       also available on-line at the GNU copyleft site ⟨http://www.gnu.org/copyleft/fdl.html⟩.

       This document is part of groff, the GNU roff distribution.  It was written by Bernd Warken
       ⟨groff-bernd.warken-72@web.de⟩; it is maintained by Werner Lemberg ⟨wl@gnu.org⟩.