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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 out-
put 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 postprocessor, this out-
put does not show up normally. This is why it is called intermediate within the groff system. The groff program pro-
vides the option -Z to inhibit postprocessing, such that the produced 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 for-
mats can be viewed directly with gxditview(1).
The main purpose of the intermediate output concept is to facilitate the development of postprocessors 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 programming language for text processing, the intermediate
output language is a kind of low-level assembler language by specifying all positions on the page for writing and draw-
ing.
The pre-groff roff versions are denoted as classical troff. The intermediate output produced by groff is fairly read-
able, 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 com-
mands with or without arguments. In this document, the term "command" always refers to the intermediate output language,
never to the roff language used for document formatting. There are commands for positioning and text writing, for draw-
ing, and for device controlling.
Separation
Classical troff output had strange requirements on whitespace. The groff output parser, however, is smart about white-
space 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 commands 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. Com-
mands 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 new-
line 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 commands were designed to request a syntac-
tical 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 split
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 indicator 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 indica-
tors 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 characters (this is,
glyphs). The names of glyphs and fonts can be of arbitrary length. A glyph 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 termi-
nated 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 commands. The groff pro-
logue 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. However, the parser for the intermediate out-
put 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, writing, and drawing com-
mands 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 loca-
tion 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 arbi-
trary 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, syn-
tactical 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 syntactical space is only necessary when two integer arguments would clash or if the preceding argu-
ment ends with a string argument.
C xxx<white-space>
Print a glyph (special character) named xxx. The trailing syntactical space or line break is necessary to allow
glyph names of arbitrary length. The glyph is printed at the current print position; the glyph's size is read
from the font file. The print position is not changed.
c c Print glyph with single-letter name c at the current print position; the glyph'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) relative 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 different 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 com-
mands 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 glyph with index n (an integer, normally non-negative) of the current font. The print position is not
changed. If -T html or -T xhtml is used, negative values are emitted also to indicate 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 classical 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 com-
patibility reasons.
p n Begin a new page in the outprint. The page number is set to n. This page is completely independent of pages for-
merly 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 xyz...<white-space>
t xyz... dummy-arg<white-space>
Print a word, i.e., a sequence of glyphs with single-letter names x, y, z, etc., 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 glyph should be printed at the current position, the current horizontal position
should then be increased by the width of the first glyph, and so on for each glyph. The widths of the glyph are
read from the font file, scaled for the current point size, and rounded to a multiple of the horizontal resolu-
tion. Special characters (glyphs with names longer than a single letter) cannot be printed using this command;
use the C command for those glyphs. This command is a groff extension; it is only used for devices whose DESC
file contains the tcommand keyword; see groff_font(5).
u n xyz...<white-space>
Print word with track kerning. This is the same as the t command except that after printing each glyph, the cur-
rent horizontal position is increased by the sum of the width of that glyph 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) relative 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 performed 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 integer 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 syntactical line break.
troff output follows the classical spacing rules (no space between command and subcommand, all arguments 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 representing a size mea-
sured in basic units u. The h arguments stand for horizontal distances where positive means right, negative left. The v
arguments 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 formatter 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 position; 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 generated by the groff escape sequences \D'F ...' and \M (with no other corre-
sponding 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 compo-
nent 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 inbetween to intermediate 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 reasons, 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 posi-
tion. 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 arbitrary 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 character. 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 writings like x i_like_groff and x roff_is_groff are accepted as well to mean the same com-
mands.
In the following, the syntax element <line-break> means a syntactical line break as defined in section 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 com-
mand 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 pro-
logue.
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 character. 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 otherwise. 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, emitting a single glyph was mostly done by a very strange command that combined a horizontal
move and the printing of a glyph. 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 glyph with single-letter name c.
In groff, arbitrary syntactical space around and within this command is allowed to be added. Only when a preced-
ing command on the same line ends with an argument of variable length a separating space is obligatory. In clas-
sical 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 glyphs 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 functionality.
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.
o 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.
o 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> "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.
o 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> "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 out-
put format is compatible with this specification except for the following features.
o The classical quasi device independence is not yet implemented.
o The old hardware was very different from what we use today. So the groff devices are also fundamentally 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 resolution of 72000 units per inch. Maybe, by implementing some rescal-
ing mechanism similar to the classical quasi device independence, these could be integrated into modern groff.
o The B-spline command D~ is correctly handled by the intermediate output parser, but the drawing routines aren't imple-
mented in some of the postprocessor programs.
o The argument of the commands s and x H has the implicit unit scaled point z in groff, while classical 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 param-
eter either did not exist, had a different name, or seem to have had a different resolution. So conflicts with classi-
cal devices are very unlikely.
o 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/1.20.1/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. This parser is the definitive 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 documentation 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 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 comprehensive documentation on the out-
put 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. Ossanna and Brian Kernighan isn't as comprehensive 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, 2005, 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 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 - published under the GPL -
that described only parts of the groff extensions of the output language. It was rewritten in 2002 by Bernd Warken and
is maintained by Werner Lemberg <wlATgnu.org>.
Groff Version 1.20.1 9 January 2009 GROFF_OUT(5)
