GROFF_OUT(5) GROFF_OUT(5)
NAME
groff_out - groff intermediate output format
DESCRIPTION
This manual page describes the intermediate output format of the GNU roff(7) text processing system
groff(1). This output is produced by a run of the GNU troff(1) program. It contains already all
device-specific information, but it is not yet fed into a device postprocessor program.
As the GNU roff processor groff(1) is a wrapper program around troff that automatically calls a post-processor, postprocessor,
processor, this output does not show up normally. This is why it is called intermediate within the
groff system. The groff program provides the option -Z to inhibit postprocessing, such that the pro-duced produced
duced intermediate output is sent to standard output just like calling troff manually.
In this document, the term troff output describes what is output by the GNU troff program, while
intermediate output refers to the language that is accepted by the parser that prepares this output
for the postprocessors. This parser is smarter on whitespace and implements obsolete elements for
compatibility, otherwise both formats are the same. Both formats can be viewed directly with
gxditview(1).
The main purpose of the intermediate output concept is to facilitate the development of postproces-sors postprocessors
sors by providing a common programming interface for all devices. It has a language of its own that
is completely different from the groff(7) language. While the groff language is a high-level pro-gramming programming
gramming language for text processing, the intermediate output language is a kind of low-level assem-bler assembler
bler language by specifying all positions on the page for writing and drawing.
The pre-groff roff versions are denoted as classical troff. The intermediate output produced by
groff is fairly readable, while classical troff output was hard to understand because of strange
habits that are still supported, but not used any longer by GNU troff.
LANGUAGE CONCEPTS
During the run of troff, the roff input is cracked down to the information on what has to be printed
at what position on the intended device. So the language of the intermediate output format can be
quite small. Its only elements are commands with or without arguments. In this document, the term
"command" always refers to the intermediate output language, never to the roff language used for doc-ument document
ument formatting. There are commands for positioning and text writing, for drawing, and for device
controlling.
Separation
Classical troff output had strange requirements on whitespace. The groff output parser, however, is
smart about whitespace by making it maximally optional. The whitespace characters, i.e., the tab,
space, and newline characters, always have a syntactical meaning. They are never printable because
spacing within the output is always done by positioning commands.
Any sequence of space or tab characters is treated as a single syntactical space. It separates com-mands commands
mands and arguments, but is only required when there would occur a clashing between the command code
and the arguments without the space. Most often, this happens when variable length command names,
arguments, argument lists, or command clusters meet. Commands and arguments with a known, fixed
length need not be separated by syntactical space.
A line break is a syntactical element, too. Every command argument can be followed by whitespace, a
comment, or a newline character. Thus a syntactical line break is defined to consist of optional
syntactical space that is optionally followed by a comment, and a newline character.
The normal commands, those for positioning and text, consist of a single letter taking a fixed number
of arguments. For historical reasons, the parser allows to stack such commands on the same line, but
fortunately, in groff intermediate output, every command with at least one argument is followed by a
line break, thus providing excellent readability.
The other commands -- those for drawing and device controlling -- have a more complicated structure;
some recognize long command names, and some take a variable number of arguments. So all D and x com-mands commands
mands were designed to request a syntactical line break after their last argument. Only one command,
`x X' has an argument that can stretch over several lines, all other commands must have all of their
arguments on the same line as the command, i.e., the arguments may not be splitted by a line break.
Empty lines, i.e., lines containing only space and/or a comment, can occur everywhere. They are just
ignored.
Argument Units
Some commands take integer arguments that are assumed to represent values in a measurement unit, but
the letter for the corresponding scale indicator is not written with the output command arguments;
see groff(7) and the groff info file for more on this topic. Most commands assume the scale indica-tor indicator
tor u, the basic unit of the device, some use z, the scaled point unit of the device, while others,
such as the color commands expect plain integers. Note that these scale indicators are relative to
the chosen device. They are defined by the parameters specified in the device's DESC file; see
groff_font(5).
Note that single characters can have the eighth bit set, as can the names of fonts and special char-acters. characters.
acters. The names of characters and fonts can be of arbitrary length. A character that is to be
printed will always be in the current font.
A string argument is always terminated by the next whitespace character (space, tab, or newline); an
embedded # character is regarded as part of the argument, not as the beginning of a comment command.
An integer argument is already terminated by the next non-digit character, which then is regarded as
the first character of the next argument or command.
Document Parts
A correct intermediate output document consists of two parts, the prologue and the body.
The task of the prologue is to set the general device parameters using three exactly specified com-mands. commands.
mands. The groff prologue is guaranteed to consist of the following three lines (in that order):
x T device
x res n h v
x init
with the arguments set as outlined in the section Device Control Commands. But the parser for the
intermediate output format is able to swallow additional whitespace and comments as well.
The body is the main section for processing the document data. Syntactically, it is a sequence of
any commands different from the ones used in the prologue. Processing is terminated as soon as the
first x stop command is encountered; the last line of any groff intermediate output always contains
such a command.
Semantically, the body is page oriented. A new page is started by a p command. Positioning, writ-ing, writing,
ing, and drawing commands are always done within the current page, so they cannot occur before the
first p command. Absolute positioning (by the H and V commands) is done relative to the current
page, all other positioning is done relative to the current location within this page.
COMMAND REFERENCE
This section describes all intermediate output commands, the classical commands as well as the groff
extensions.
Comment Command
#anything<end_of_line>
A comment. Ignore any characters from the # character up to the next newline character.
This command is the only possibility for commenting in the intermediate output. Each comment can be
preceded by arbitrary syntactical space; every command can be terminated by a comment.
Simple Commands
The commands in this subsection have a command code consisting of a single character, taking a fixed
number of arguments. Most of them are commands for positioning and text writing. These commands are
smart about whitespace. Optionally, syntactical space can be inserted before, after, and between the
command letter and its arguments. All of these commands are stackable, i.e., they can be preceded by
other simple commands or followed by arbitrary other commands on the same line. A separating syntac-tical syntactical
tical space is only necessary when two integer arguments would clash or if the preceding argument
ends with a string argument.
C xxx<white_space>
Print a special groff character named xxx. The trailing syntactical space or line break is
necessary to allow character names of arbitrary length. The character is printed at the cur-rent current
rent print position; the character's size is read from the font file. The print position is
not changed.
c c Print character c at the current print position; the character's size is read from the font
file. The print position is not changed.
f n Set font to font number n (a non-negative integer).
H n Move right to the absolute vertical position n (a non-negative integer in basic units u) rela-tive relative
tive to left edge of current page.
h n Move n (a non-negative integer) basic units u horizontally to the right. [CSTR #54] allows
negative values for n also, but groff doesn't use this.
m color_scheme [component ...]
Set the color for text (glyphs), line drawing, and the outline of graphic objects using dif-ferent different
ferent color schemes; the analoguous command for the filling color of graphic objects is DF.
The color components are specified as integer arguments between 0 and 65536. The number of
color components and their meaning vary for the different color schemes. These commands are
generated by the groff escape sequence \m. No position changing. These commands are a groff
extension.
mc cyan magenta yellow
Set color using the CMY color scheme, having the 3 color components cyan, magenta, and
yellow.
md Set color to the default color value (black in most cases). No component arguments.
mg gray
Set color to the shade of gray given by the argument, an integer between 0 (black) and
65536 (white).
mk cyan magenta yellow black
Set color using the CMYK color scheme, having the 4 color components cyan, magenta,
yellow, and black.
mr red green blue
Set color using the RGB color scheme, having the 3 color components red, green, and
blue.
N n Print character with index n (an integer, normally non-negative) of the current font. The
print position is not changed. If -T html is used, negative values are emitted also to indi-cate indicate
cate an unbreakable space with given width. For example, N -193 represents an unbreakable
space which has a width of 193u. This command is a groff extension.
n b a Inform the device about a line break, but no positioning is done by this command. In classi-cal classical
cal troff, the integer arguments b and a informed about the space before and after the current
line to make the intermediate output more human readable without performing any action. In
groff, they are just ignored, but they must be provided for compatibility reasons.
p n Begin a new page in the outprint. The page number is set to n. This page is completely inde-pendent independent
pendent of pages formerly processed even if those have the same page number. The vertical
position on the outprint is automatically set to 0. All positioning, writing, and drawing is
always done relative to a page, so a p command must be issued before any of these commands.
s n Set point size to n scaled points (this is unit z in GNU troff). Classical troff used the
unit points (p) instead; see section COMPATIBILITY.
t xxx<white_space>
t xxx dummy_arg<white_space>
Print a word, i.e., a sequence of characters xxx terminated by a space character or a line
break; an optional second integer argument is ignored (this allows the formatter to generate
an even number of arguments). The first character should be printed at the current position,
the current horizontal position should then be increased by the width of the first character,
and so on for each character. The widths of the characters are read from the font file,
scaled for the current point size, and rounded to a multiple of the horizontal resolution.
Special characters cannot be printed using this command (use the C command for named charac-ters). characters).
ters). This command is a groff extension; it is only used for devices whose DESC file con-tains contains
tains the tcommand keyword; see groff_font(5).
u n xxx<white_space>
Print word with track kerning. This is the same as the t command except that after printing
each character, the current horizontal position is increased by the sum of the width of that
character and n (an integer in basic units u). This command is a groff extension; it is only
used for devices whose DESC file contains the tcommand keyword; see groff_font(5).
V n Move down to the absolute vertical position n (a non-negative integer in basic units u) rela-tive relative
tive to upper edge of current page.
v n Move n basic units u down (n is a non-negative integer). [CSTR #54] allows negative values
for n also, but groff doesn't use this.
w Informs about a paddable whitespace to increase readability. The spacing itself must be per-formed performed
formed explicitly by a move command.
Graphics Commands
Each graphics or drawing command in the intermediate output starts with the letter D followed by one
or two characters that specify a subcommand; this is followed by a fixed or variable number of inte-ger integer
ger arguments that are separated by a single space character. A D command may not be followed by
another command on the same line (apart from a comment), so each D command is terminated by a syntac-tical syntactical
tical line break.
troff output follows the classical spacing rules (no space between command and subcommand, all argu-ments arguments
ments are preceded by a single space character), but the parser allows optional space between the
command letters and makes the space before the first argument optional. As usual, each space can be
any sequence of tab and space characters.
Some graphics commands can take a variable number of arguments. In this case, they are integers rep-resenting representing
resenting a size measured in basic units u. The arguments called , , ..., h1, h2, ..., hn stand for
horizontal distances where positive means right, negative left. The arguments called , , ..., v1,
v2, ..., vn stand for vertical distances where positive means down, negative up. All these distances
are offsets relative to the current location.
Unless indicated otherwise, each graphics command directly corresponds to a similar groff \D escape
sequence; see groff(7).
Unknown D commands are assumed to be device-specific. Its arguments are parsed as strings; the whole
information is then sent to the postprocessor.
In the following command reference, the syntax element <line_break> means a syntactical line break as
defined in section Separation.
D~ h1 v1 h2 v2 ... hn vn<line_break>
Draw B-spline from current position to offset (h1, v1), then to offset (h2, v2) if given, etc.
up to (hn, vn). This command takes a variable number of argument pairs; the current position
is moved to the terminal point of the drawn curve.
Da h1 v1 h2 v2<line_break>
Draw arc from current position to (h1, v1)+(h2, v2) with center at (h1, v1); then move the
current position to the final point of the arc.
DC d<line_break>
DC d dummy_arg<line_break>
Draw a solid circle using the current fill color with diameter d (integer in basic units u)
with leftmost point at the current position; then move the current position to the rightmost
point of the circle. An optional second integer argument is ignored (this allows to the for-matter formatter
matter to generate an even number of arguments). This command is a groff extension.
Dc d<line_break>
Draw circle line with diameter d (integer in basic units u) with leftmost point at the current
position; then move the current position to the rightmost point of the circle.
DE h v<line_break>
Draw a solid ellipse in the current fill color with a horizontal diameter of h and a vertical
diameter of v (both integers in basic units u) with the leftmost point at the current posi-tion; position;
tion; then move to the rightmost point of the ellipse. This command is a groff extension.
De h v<line_break>
Draw an outlined ellipse with a horizontal diameter of h and a vertical diameter of v (both
integers in basic units u) with the leftmost point at current position; then move to the
rightmost point of the ellipse.
DF color_scheme [component ...]<line_break>
Set fill color for solid drawing objects using different color schemes; the analoguous command
for setting the color of text, line graphics, and the outline of graphic objects is m. The
color components are specified as integer arguments between 0 and 65536. The number of color
components and their meaning vary for the different color schemes. These commands are gener-ated generated
ated by the groff escape sequences \D'F ...' and \M (with no other corresponding graphics
commands). No position changing. This command is a groff extension.
DFc cyan magenta yellow<line_break>
Set fill color for solid drawing objects using the CMY color scheme, having the 3 color
components cyan, magenta, and yellow.
DFd <line_break>
Set fill color for solid drawing objects to the default fill color value (black in most
cases). No component arguments.
DFg gray<line_break>
Set fill color for solid drawing objects to the shade of gray given by the argument, an
integer between 0 (black) and 65536 (white).
DFk cyan magenta yellow black<line_break>
Set fill color for solid drawing objects using the CMYK color scheme, having the
4 color components cyan, magenta, yellow, and black.
DFr red green blue<line_break>
Set fill color for solid drawing objects using the RGB color scheme, having the 3 color
components red, green, and blue.
Df n<line_break>
The argument n must be an integer in the range -32767 to 32767.
0 <= n <= 1000
Set the color for filling solid drawing objects to a shade of gray, where 0 corresponds
to solid white, 1000 (the default) to solid black, and values in between to intermedi-
ate shades of gray; this is obsoleted by command DFg.
n < 0 or n > 1000
Set the filling color to the color that is currently being used for the text and the
outline, see command m. For example, the command sequence
mg 0 0 65536
Df -1
sets all colors to blue.
No position changing. This command is a groff extension.
Dl h v<line_break>
Draw line from current position to offset (h, v) (integers in basic units u); then set current
position to the end of the drawn line.
Dp h1 v1 h2 v2 ... hn vn<line_break>
Draw a polygon line from current position to offset (h1, v1), from there to offset (h2, v2),
etc. up to offset (hn, vn), and from there back to the starting position. For historical rea-sons, reasons,
sons, the position is changed by adding the sum of all arguments with odd index to the actual
horizontal position and the even ones to the vertical position. Although this doesn't make
sense it is kept for compatibility. This command is a groff extension.
DP h1 v1 h2 v2 ... hn vn<line_break>
The same macro as the corresponding Dp command with the same arguments, but draws a solid
polygon in the current fill color rather than an outlined polygon. The position is changed in
the same way as with Dp. This command is a groff extension.
Dt n<line_break>
Set the current line thickness to n (an integer in basic units u) if n>0; if n=0 select the
smallest available line thickness; if n<0 set the line thickness proportional to the point
size (this is the default before the first Dt command was specified). For historical reasons,
the horizontal position is changed by adding the argument to the actual horizontal position,
while the vertical position is not changed. Although this doesn't make sense it is kept for
compatibility. This command is a groff extension.
Device Control Commands
Each device control command starts with the letter x followed by a space character (optional or arbi-
trary space/tab in groff) and a subcommand letter or word; each argument (if any) must be preceded by
a syntactical space. All x commands are terminated by a syntactical line break; no device control
command can be followed by another command on the same line (except a comment).
The subcommand is basically a single letter, but to increase readability, it can be written as a
word, i.e., an arbitrary sequence of characters terminated by the next tab, space, or newline charac-ter. character.
ter. All characters of the subcommand word but the first are simply ignored. For example, troff
outputs the initialization command x i as x init and the resolution command x r as x res. But writ-ings writings
ings like x i_like_groff and x roff_is_groff resp. are accepted as well to mean the same commands.
In the following, the syntax element <line_break> means a syntactical line break as defined in sec-tion section
tion Separation.
xF name<line_break>
(Filename control command)
Use name as the intended name for the current file in error reports. This is useful for
remembering the original file name when groff uses an internal piping mechanism. The input
file is not changed by this command. This command is a groff extension.
xf n s<line_break>
(font control command)
Mount font position n (a non-negative integer) with font named s (a text word), cf.
groff_font(5).
xH n<line_break>
(Height control command)
Set character height to n (a positive integer in scaled points z). Classical troff used the
unit points (p) instead; see section COMPATIBILITY.
xi<line_break>
(init control command)
Initialize device. This is the third command of the prologue.
xp<line_break>
(pause control command)
Parsed but ignored. The classical documentation reads pause device, can be restarted.
xr n h v<line_break>
(resolution control command)
Resolution is n, while h is the minimal horizontal motion, and v the minimal vertical motion
possible with this device; all arguments are positive integers in basic units u per inch.
This is the second command of the prologue.
xS n<line_break>
(Slant control command)
Set slant to n degrees (an integer in basic units u).
xs<line_break>
(stop control command)
Terminates the processing of the current file; issued as the last command of any intermediate
troff output.
xt<line_break>
(trailer control command)
Generate trailer information, if any. In groff, this is actually just ignored.
xT xxx<line_break>
(Typesetter control command)
Set name of device to word xxx, a sequence of characters ended by the next whitespace charac-ter. character.
ter. The possible device names coincide with those from the groff -T option. This is the
first command of the prologue.
xu n<line_break>
(underline control command)
Configure underlining of spaces. If n is 1, start underlining of spaces; if n is 0, stop
underlining of spaces. This is needed for the cu request in nroff mode and is ignored other-wise. otherwise.
wise. This command is a groff extension.
xX anything<line_break>
(X-escape control command)
Send string anything uninterpreted to the device. If the line following this command starts
with a + character this line is interpreted as a continuation line in the following sense.
The + is ignored, but a newline character is sent instead to the device, the rest of the line
is sent uninterpreted. The same applies to all following lines until the first character of a
line is not a + character. This command is generated by the groff escape sequence \X. The
line-continuing feature is a groff extension.
Obsolete Command
In classical troff output, the writing of a single character was mostly done by a very strange com-mand command
mand that combined a horizontal move and the printing of a character. It didn't have a command code,
but is represented by a 3-character argument consisting of exactly 2 digits and a character.
ddc Move right dd (exactly two decimal digits) basic units u, then print character c.
In groff, arbitrary syntactical space around and within this command is allowed to be added.
Only when a preceding command on the same line ends with an argument of variable length a sep-arating separating
arating space is obligatory. In classical troff, large clusters of these and other commands
were used, mostly without spaces; this made such output almost unreadable.
For modern high-resolution devices, this command does not make sense because the width of the charac-ters characters
ters can become much larger than two decimal digits. In groff, this is only used for the devices
X75, X75-12, X100, and X100-12. For other devices, the commands t and u provide a better functional-ity. functionality.
ity.
POSTPROCESSING
The roff postprocessors are programs that have the task to translate the intermediate output into
actions that are sent to a device. A device can be some piece of hardware such as a printer, or a
software file format suitable for graphical or text processing. The groff system provides powerful
means that make the programming of such postprocessors an easy task.
There is a library function that parses the intermediate output and sends the information obtained to
the device via methods of a class with a common interface for each device. So a groff postprocessor
must only redefine the methods of this class. For details, see the reference in section FILES.
EXAMPLES
This section presents the intermediate output generated from the same input for three different
devices. The input is the sentence hell world fed into groff on the command line.
High-resolution device ps
shell> echo hell world | groff -Z -T ps
x T ps
x res 72000 1 1
x init
p1
x font 5 TR
f5
s10000
V12000
H72000
thell
wh2500
tw
H96620
torld
n12000 0
x trailer
V792000
x stop
This output can be fed into the postprocessor grops(1) to get its representation as a PostScript
file.
Low-resolution device latin1
This is similar to the high-resolution device except that the positioning is done at a minor scale.
Some comments (lines starting with #) were added for clarification; they were not generated by the
formatter.
shell> echo hell world | groff -Z -T latin1
# prologue
x T latin1
x res 240 24 40
x init
# begin a new page
p1
# font setup
x font 1 R
f1
s10
# initial positioning on the page
V40
H0
# write text `hell'
thell
# inform about a space, and do it by a horizontal jump
wh24
# write text `world'
tworld
# announce line break, but do nothing because ...
n40 0
# ... the end of the document has been reached
x trailer
V2640
x stop
This output can be fed into the postprocessor grotty(1) to get a formatted text document.
Classical style output
As a computer monitor has a very low resolution compared to modern printers the intermediate output
for the X devices can use the jump-and-write command with its 2-digit displacements.
shell> echo hell world | groff -Z -T X100
x T X100
x res 100 1 1
x init
p1
x font 5 TR
f5
s10
V16
H100
# write text with old-style jump-and-write command
ch07e07l03lw06w11o07r05l03dh7
n16 0
x trailer
V1100
x stop
This output can be fed into the postprocessor xditview(1x) or gxditview(1) for displaying in X.
Due to the obsolete jump-and-write command, the text clusters in the classical output are almost
unreadable.
COMPATIBILITY
The intermediate output language of the classical troff was first documented in [CSTR #97]. The
groff intermediate output format is compatible with this specification except for the following fea-tures. features.
tures.
The classical quasi device independence is not yet implemented.
The old hardware was very different from what we use today. So the groff devices are also funda-mentally fundamentally
mentally different from the ones in classical troff. For example, the classical PostScript device
was called post and had a resolution of 720 units per inch, while groff's ps device has a resolu-tion resolution
tion of 72000 units per inch. Maybe, by implementing some rescaling mechanism similar to the clas-sical classical
sical quasi device independence, these could be integrated into modern groff.
The B-spline command D~ is correctly handled by the intermediate output parser, but the drawing
routines aren't implemented in some of the postprocessor programs.
The argument of the commands s and x H has the implicit unit scaled point z in groff, while classi-cal classical
cal troff had point (p). This isn't an incompatibility, but a compatible extension, for both units
coincide for all devices without a sizescale parameter, including all classical and the groff text
devices. The few groff devices with a sizescale parameter either did not exist, had a different
name, or seem to have had a different resolution. So conflicts with classical devices are very
unlikely.
The position changing after the commands Dp, DP, and Dt is illogical, but as old versions of groff
used this feature it is kept for compatibility reasons.
The differences between groff and classical troff are documented in groff_diff(7).
FILES
/usr/share/groff/1.19.2/font/devname/DESC
Device description file for device name.
<groff_source_dir>/src/libs/libdriver/input.cpp
Defines the parser and postprocessor for the intermediate output. It is located relative to
the top directory of the groff source tree, e.g. @GROFFSRCDIR@. This parser is the defini-tive definitive
tive specification of the groff intermediate output format.
SEE ALSO
A reference like groff(7) refers to a manual page; here groff in section 7 of the man-page documenta-tion documentation
tion system. To read the example, look up section 7 in your desktop help system or call from the
shell prompt
shell> man 7 groff
For more details, see man(1).
groff(1)
option -Z and further readings on groff.
groff(7)
for details of the groff language such as numerical units and escape sequences.
groff_font(5)
for details on the device scaling parameters of the DESC file.
troff(1)
generates the device-independent intermediate output.
roff(7)
for historical aspects and the general structure of roff systems.
groff_diff(7)
The differences between the intermediate output in groff and classical troff.
gxditview(1)
Viewer for the intermediate output.
grodvi(1), grohtml(1), grolbp(1), grolj4(1), grops(1), grotty(1)
the groff postprocessor programs.
For a treatment of all aspects of the groff system within a single document, see the groff info file.
It can be read within the integrated help systems, within emacs(1) or from the shell prompt by
shell> info groff
The classical troff output language is described in two AT&T Bell Labs CSTR documents available on-line online
line at Bell Labs CSTR site <http://cm.bell-labs.com/cm/cs/cstr.html.
[CSTR #97]
A Typesetter-independent TROFF by Brian Kernighan is the original and most concise documenta-tion documentation
tion on the output language; see CSTR #97 <http://cm.bell-labs.com/cm/cs/cstr/97.ps.gz.
[CSTR #54]
The 1992 revision of the Nroff/Troff User's Manual by J. F. Osanna and Brian Kernighan isn't
as concise as [CSTR #97] regarding the output language; see CSTR #54 <http://cm.bell-labs.com/
cm/cs/cstr/54.ps.gz.
AUTHORS
Copyright (C) 1989, 2001, 2002, 2003, 2004 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 with this package; 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 is based on a former version - pub-lished published
lished under the GPL - that described only parts of the groff extensions of the output language. It
has been rewritten 2002 by Bernd Warken and is maintained by
Werner Lemberg <wl@gnu.org>.
Groff Version 1.19.2 3 July 2005 GROFF_OUT(5)
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