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
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 groffsystem. 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
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
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 GNUtroff.
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.
SeparationClassical 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
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
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
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.
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
indicators are relative to the chosen device. They are defined by
the parameters specified in the device's DESC file; see
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.
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 devicex res n h vx init
with the arguments set as outlined in the section Device ControlCommands. 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 groffintermediate 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.
This section describes all intermediate output commands, the
classical commands as well as the groff extensions.
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.
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.
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
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.
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
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
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
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
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
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
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 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
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.
Set fill color for solid drawing objects to the default
fill color value (black in most cases). No component
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,
The argument n must be an integer in the range -32767 to
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
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
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
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
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.
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 posi‐
tion is changed by adding the argument to the actual horizon‐
tal 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 sub‐
command letter or word; each argument (if any) must be preceded by a
syntactical space. All x commands are terminated by a syntacticalline break; no device control command can be followed by another com‐
mand on the same line (except a comment).
The subcommand is basically a single letter, but to increase read‐
ability, 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
In the following, the syntax element ⟨line-break⟩ means a syntacticalline break as defined in section Separation.
(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
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).
(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.
(init control command)
Initialize device. This is the third command of the prologue.
(pause control command)
Parsed but ignored. The classical documentation reads pausedevice, 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.
(Slant control command)
Set slant to n degrees (an integer in basic units u).
(stop control command)
Terminates the processing of the current file; issued as the
last command of any intermediate troff output.
(trailer control command)
Generate trailer information, if any. In groff, this is actu‐
ally just ignored.
(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.
(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. This command is a groff extension.
(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.
In classical troff output, emitting a single glyph was mostly done by
a very strange command that combined a horizontal move and the print‐
ing 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 charac‐
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 deci‐
mal 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
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.
This section presents the intermediate output generated from the same
input for three different devices. The input is the sentence hellworld fed into groff on the command line.
· High-resolution device psshell> echo "hell world" | groff -Z -T ps
x T psx res 72000 1 1x initp1x font 5 TRf5s10000V12000H72000thellwh2500twH96620torldn12000 0x trailerV792000x 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
· Low-resolution device latin1
This is similar to the high-resolution device except that the posi‐
tioning is done at a minor scale. Some comments (lines starting
with #) were added for clarification; they were not generated by
shell> "hell world" | groff -Z -T latin1
# prologuex T latin1x res 240 24 40x init# begin a new pagep1# font setupx font 1 Rf1s10# initial positioning on the pageV40H0# write text ‘hell’thell# inform about a space, and do it by a horizontal jumpwh24# write text ‘world’tworld# announce line break, but do nothing because ...n40 0# ... the end of the document has been reachedx trailerV2640x stop
This output can be fed into the postprocessor grotty(1) to get a for‐
matted 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 X100x res 100 1 1x initp1x font 5 TRf5s10V16H100# write text with old-style jump-and-write commandch07e07l03lw06w11o07r05l03dh7n16 0x trailerV1100x 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.
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
· The B-spline command D~ is correctly handled by the intermediateoutput 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
Device description file for device name.
Defines the parser and postprocessor for the intermediateoutput. 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.
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
shell> man 7 groff
For more details, see man(1).
option -Z and further readings on groff.
for details of the groff language such as numerical units and
for details on the device scaling parameters of the DESC file.
generates the device-independent intermediate output.
for historical aspects and the general structure of roff sys‐
The differences between the intermediate output in groff and
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 inte‐
grated 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
[CSTR #97]A Typesetter-independent TROFF by Brian Kernighan is the orig‐
inal and most comprehensive documentation on the output lan‐
guage; see CSTR #97
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
This page is part of the groff (GNU troff) project. Information
about the project can be found at
⟨http://www.gnu.org/software/groff/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/groff/⟩. This
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⟨ftp://ftp.gnu.org/gnu/groff/⟩ on 2016-10-04. If you discover any
rendering problems in this HTML version of the page, or you believe
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corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
Groff Version 1.22.3 4 November 2014 GROFF_OUT(5)