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” below. 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.

There is a free archive about historical RUNOFF documents. You can get it anonymously by the shell
command
$git clone https://github.com/bwarken/RUNOFF_historical.git

As well, there is a new project for writing a program that can read RUNOFF files , but it does not yet
work so far. You can get an early version anonymously by the shell command
$git clone https://github.com/bwarken/runoff.git

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” below. 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.
Nowadays, it is accessible again (on-line) for non-commercial use; see SEE ALSO, below.

groff — free GNU 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.

Free Heirloom roff
An alternative is Gunnar Ritter's Heirloom roff project 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. You can get this package with the shell command:
$ git clone https://github.com/n-t-roff/heirloom-doctools

Moreover, one finds there the Original Documenter's Workbench Release 3.3.

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. 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 formulae.
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.

       More details for file name extensions can be found at groff_filenames(5).

EDITING ROFF

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 judicious line breaking in a roff input file.

This is an example of a
.I roff
document that you can type into your text editor.
.
This is the next sentence in the same paragraph.
.
This is a longer sentence stretching over several input lines;
abbreviations like cf. are easily identified because the dot is
not followed by a line break.
.
In the output, this sentence continues the same paragraph.

Editing with Emacs
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 press 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.

Editing with Vim
Besides Emacs, some other editors provide nroff style files too, e.g. vim(1), an extension of the vi(1)
program. Vim's highlighting can be made to recognize roff files by setting the filetype option in a Vim
modeline. For this feature to work, your copy of vim must be built with support for, and configured to
enable, several features; consult the editor's online help topics “auto-setting”, “filetype”, and
“syntax”. Then put the following at the end of your roff files, after any Emacs configuration:

.\" vim: set filetype=groff:

Replace “groff” in the above with “nroff” if you want highlighing that does not recognize many of the GNU
extensions to roff, such as request, register, and string names longer than two characters.

AUTHORS

       This document was written by Bernd Warken.