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 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 sytem 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 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
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.
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¶
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. |
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 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 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:
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
- 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.
SEE ALSO¶
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¶
- troff.org
The historical troff site provides
an overview and pointers to all historical aspects of
roff.
- Multics
The Multics site 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
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
- Developers at AT&T Bell Labs
Bell Labs Computing and
Mathematical Sciences Research provides a search facility for tracking
information on the early developers.
- Plan 9
The Plan 9 operating
system by AT&T Bell Labs.
- runoff
Jerry
Saltzer's home page stores some documents using the ancient RUNOFF
formatting language.
- CSTR Papers
The Bell Labs CSTR
site stores the original
troff manuals (CSTR #54, #97, #114, #116,
#122) and famous historical documents on programming.
- GNU roff
The groff web site
provides the free
roff implementation
groff, the actual standard
roff.
Historical roff Documentation¶
Many classical
troff documents are still available on-line. The two main
manuals of the
troff language are
- [CSTR #54]
- J. F. Ossanna,
Nroff/Troff
User's Manual Bell Labs, 1976; revised by Brian Kernighan, 1992.
- [CSTR #97]
- Brian Kernighan,
A
Typesetter-independent TROFF 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 Bell Labs, August 1984.
- [CSTR #116]
- Brian W. Kernighan,
PIC –
A Graphics Language for Typesetting 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 Bell Labs, April 1986.
Manual Pages¶
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.
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
This document is part of
groff, the GNU
roff distribution. It was
written by Bernd Warken it is maintained by Werner Lemberg