roff - concepts and history of roff typesetting
roff is the general name for a set of type-setting programs, known
under names like troff, nroff, ditroff, groff, etc. A roff type-setting
system consists of an extensible text formatting language and a
set of programs for printing and converting to other text formats.
Traditionally, it is the main text processing system of Unix; every
Unix-like operating system still distributes a roff system as a core
package.
The most common roff system today is the free software implementation
GNU roff, groff(1). The pre-groff implementations are referred to as
classical (dating back as long as 1973). groff implements the lookand-feel
and functionality of its classical ancestors, but has many
extensions. As groff is the only roff system that is available for
every (or almost every) computer system it is the de-facto roff standard
today.
In some ancient Unix systems, there was a binary called roff that
implemented the even more ancient runoff of the Multics operating system,
cf. section HISTORY. The functionality of this program was very
restricted even in comparison to ancient troff; it is not supported any
longer. Consequently, in this document, the term roff always refers to
the general meaning of roff system, not to the ancient roff binary.
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.
The most popular application of roff is the concept of manual pages or
shortly man pages; this is the standard documentation system on many
operating systems.
This document describes the historical facts around 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); an general overview of the formatting language; some
tips for editing roff files; and many pointers to further readings.
The roff text processing system has a very long history, dating 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 [Toc] [Back]
The evolution of roff is intimately related to the history of the operating
systems. Its predecessor runoff was written by Jerry Saltzer on
the CTSS operating system (Compatible Time Sharing System) as early as
1961. When CTSS was further developed into the operating system Multics
<http://www.multicians.org>, the famous predecessor of Unix from
1963, runoff became the main format for documentation and text processing.
Both operating systems could only be run on very expensive computers
at that time, so they were mostly used in research and for official
and military tasks.
The possibilities of the runoff language were quite limited as compared
to modern roff. Only text output was possible in the 1960s. This
could be implemented by a set of requests of length 2, many of which
are still identically used in roff. The language was modelled according
to the habits of typesetting in the pre-computer age, where lines
starting with a dot were used in manuscripts to denote formatting
requests to the person who would perform the typesetting manually later
on.
The runoff program was written in the PL/1 language first, later on in
BCPL, the grandmother of the C programming language. In the Multics
operating system, the help system was handled by runoff, similar to
roff's task to manage the Unix manual pages. There are still documents
written in the runoff language; for examples see Saltzer's home page,
cf. section SEE ALSO.
The Classical nroff/troff System
In the 1970s, the Multics off-spring Unix became more and more popular
because it could be run on affordable machines and was easily available
for universities at that time. At MIT (the Massachusetts Institute of
Technology), there was a need to drive the Wang 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 Josef F. Osanna, a main
developer of the Multics operating system and programmer of several
runoff ports.
The name runoff was shortened to roff. The greatly enlarged language
of Osanna's concept included already all elements of a full roff sys-
tem. All modern roff systems try to implement compatibility to this
system. So Joe Osanna 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 sytem as
a whole.
Osanna 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 Osanna had died in 1977 by a heart-attack at the age of about 50,
Kernighan went on with developing troff. The next milestone was to
equip 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.
Commercialization [Toc] [Back]
A major degradation occurred when the easily available Unix 7 operating
system was commercialized. A whole bunch of divergent operating systems
emerged, fighting each other with incompatibilities in their
extensions. Luckily, the incompatibilities did not fight the original
troff. All of the different commercial roff systems made heavy use of
Osanna/Kernighan's open source code and documentation, but sold them as
"their" system -- with only minor additions.
The source code of both the ancient Unix and classical troff weren't
available for two decades. Fortunately, Caldera bought SCO UNIX in
2001. In the following, Caldera made the ancient source code accessible
on-line for non-commercial use, cf. section SEE ALSO.
Free roff [Toc] [Back]
None of the commercial roff systems could attain the status of a successor
for the general roff development. Everyone was only interested
in their own stuff. This led to a steep downfall of the once excellent
Unix operating system during the 1980s.
As a counter-measure to the galopping commercialization, AT&T Bell Labs
tried to launch a rescue project with their Plan 9 operating system.
It is freely available for non-commercial use, even the source code,
but has a proprietary license that empedes the free development. This
concept is outdated, so Plan 9 was not accepted as a platform to bundle
the main-stream development.
The only remedy came from the emerging free operatings systems (386BSD,
GNU/Linux, etc.) and software projects during the 1980s and 1990s.
These implemented the ancient Unix features and many extensions, such
that the old experience is not lost. In the 21st century, Unix-like
systems are again a major factor in computer industry -- thanks to free
software.
The most important free roff project was the GNU port of troff, created
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.
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 [Toc] [Back]
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.
sh# cat file | ... | preproc | ... | troff options | postproc
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 [Toc] [Back]
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 formulae
pic for drawing diagrams
refer for bibliographic references
soelim for including macro files from standard locations
Other known preprocessors that are not available on all systems include
chem for drawing chemical formulae.
grap for constructing graphical elements.
grn for including gremlin(1) pictures.
Formatter Programs [Toc] [Back]
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 [Toc] [Back]
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, while groff's ps device has 72000, a refinement of factor
100.
Today the operating systems provide device drivers for most printerlike
hardware, so it isn't necessary to write a special hardware postprocessor
for each printer.
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 [Toc] [Back]
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 [Toc] [Back]
The classical roff formatting language is documented in the Troff Us-
er'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 nonASCII
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.
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 commandline
pipe that is specified in the shell environment variable LESSOPEN.
This process is not well documented, so here an example:
sh# LESSOPEN='|lesspipe %s'
where lesspipe is either a system supplied command or a shell script of
your own.
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.
o The most general method is to include the following 3 comment lines
at the end of the file.
.\" Local Variables:
.\" mode: nroff
.\" End:
o There is a set of file name extensions, e.g. the man pages that trigger
the automatic activation of the nroff mode.
o 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.
o 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.
o 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.
o 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.
o 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 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.
UNIX(R) is a registered trademark of the Open Group. But things have
improved considerably after Caldera had bought SCO UNIX in 2001.
There is a lot of documentation on roff. The original papers on classical
troff are still available, and all aspects of groff are documented
in great detail.
Internet sites [Toc] [Back]
troff.org
The historical troff site <http://www.troff.org> provides an
overview and pointers to all historical aspects of roff.
Multics
The Multics site <http://www.multicians.org> contains a lot of
information on the MIT projects, CTSS, Multics, early Unix, including
runoff; especially useful are a glossary and the many
links to ancient documents.
Unix Archive
The Ancient Unixes Archive <http://www.tuhs.org/Archive/> provides
the source code and some binaries of the ancient Unixes
(including the source code of troff and its documentation) that
were made public by Caldera since 2001, e.g. of the famous Unix
version 7 for PDP-11 at the Unix V7 site <http://www.tuhs.org/
Archive/PDP-11/Trees/V7>.
Developers at AT&T Bell Labs
Bell Labs Computing and Mathematical Sciences Research <http://
cm.bell-labs.com/cm/index.html> provides a search facility for
tracking information on the early developers.
Plan 9 The Plan 9 operating system <http://plan9.bell-labs.com> by AT&T
Bell Labs.
runoff Jerry Saltzer's home page <http://web.mit.edu/Saltzer/www/
publications/pubs.html> stores some documents using the ancient
runoff formatting language.
CSTR Papers
The Bell Labs CSTR site <http://cm.bell-labs.com/cm/cs/
cstr.html> stores the original troff manuals (CSTR #54, #97,
#114, #116, #122) and famous historical documents on programming.
GNU roff
The groff web site <http://www.gnu.org/software/groff> provides
the free roff implementation groff, the actual standard roff.
Historical roff Documentation [Toc] [Back]
Many classical documents are still available on-line. The two main
manuals of the troff language are
[CSTR #54]
J. F. Osanna, Nroff/Troff User's Manual <http://
cm.bell-labs.com/cm/cs/54.ps>; Bell Labs, 1976; revised by Brian
Kernighan, 1992.
[CSTR #97]
Brian Kernighan, A Typesetter-independent TROFF <http://
cm.bell-labs.com/cm/cs/97.ps>, Bell Labs, 1981, revised March
1982.
The "little language" roff papers are
[CSTR #114]
Jon L. Bentley and Brian W. Kernighan, GRAP -- A Language for
Typesetting Graphs <http://cm.bell-labs.com/cm/cs/114.ps>; Bell
Labs, August 1984.
[CSTR #116]
Brian W. Kernighan, PIC -- A Graphics Language for Typesetting
<http://cm.bell-labs.com/cm/cs/116.ps>; Bell Labs, December
1984.
[CSTR #122]
J. L. Bentley, L. W. Jelinski, and B. W. Kernighan, CHEM -- A
Program for Typesetting Chemical Structure Diagrams, Computers
and Chemistry <http://cm.bell-labs.com/cm/cs/122.ps>; Bell Labs,
April 1986.
Manual Pages [Toc] [Back]
Due to its complex structure, a full roff system has many man pages,
each describing a single aspect of roff. Unfortunately, there is no
general naming scheme for the documentation among the different roff
implementations.
In groff, the man page groff(1) contains a survey of all documentation
available in groff.
On other systems, you are on your own, but troff(1) might be a good
starting point.
Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc.
This document is distributed under the terms of the FDL (GNU Free Documentation
License) version 1.1 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 <bwarken@mayn.de>; it is maintained by Werner
Lemberg <wl@gnu.org>.
Groff Version 1.19 1 May 2003 ROFF(7)
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