Provided by: groff_1.22.4-4build1_amd64 
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 postprocessor, 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 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
formats 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 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 document 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 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.
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 stacking of 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 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 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 Groff: The GNU Implementation of troff, the groff
Texinfo manual, 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 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 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 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 commands. 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 subsection “Device Control Commands” below.
However, 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, writing, 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 syntactical 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 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 analogous 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 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 compatibility reasons.
p n Begin a new page in the outprint. The page number is set to n. This page is
completely independent 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” below.
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 resolution.
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 current 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 measured 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 subsection “Separation” above.
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 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
analogous 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 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 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 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 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 commands.
In the following, the syntax element ⟨line-break⟩ means a syntactical line break as
defined in subsection “Separation” above.
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); see
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” below.
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 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 preceding command on the same line ends with an argument of
variable length a separating 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 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” below.
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, or gropdf(1) to output directly to PDF.
• 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.
• 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 output format is compatible with this specification except for
the following features.
• 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 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 rescaling mechanism similar to the classical 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 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 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/1.22.4/font/devname/DESC
Device description file for device name.
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.
AUTHORS
James Clark wrote an early version of this document, which described only the differences
between ditroff(7)'s output format and that of GNU roff. The present version was
completely rewritten in 2001 by Bernd Warken ⟨groff-bernd.warken-72@web.de⟩.
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.
Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner Lemberg, is the
primary groff manual. You can browse it interactively with “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 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. 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⟩.