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 Users 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.
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
Users 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.
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 Users 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