groff_out - groff intermediate output format
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.
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.
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 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 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.
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 \$@ the basic unit of the device, some
use \$@ 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. 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.
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 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, 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.
- #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.
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.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Print a special groff character named The trailing syntactical
space or line break is necessary to allow character names of
arbitrary length. The character is printed at the current print position;
the character's size is read from the font file. The print position is not
changed.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Print character at the current print position; the character's size
is read from the font file. The print position is not changed.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set font to font number (a non-negative integer).
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Move right to the absolute vertical position (a non-negative
integer in basic units \$@ relative to left edge of current
page.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Move (a non-negative integer) basic units \$@ horizontally
to the right. [CSTR #54] allows negative values for n
also, but groff doesn't use this.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- 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 commands are a groff extension.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set color using the CMY color scheme, having the 3 color components
cyan, magenta, and yellow.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set color to the default color value (black in most cases). No component
arguments.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set color to the shade of gray given by the argument, an integer between 0
(black) and 65536 (white).
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set color using the CMYK color scheme, having the 4 color
components cyan, magenta, yellow, and black.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set color using the RGB color scheme, having the 3 color components
red, green, and blue.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Print character with index (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
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.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Inform the device about a line break, but no positioning is done by this
command. In classical troff, the integer arguments
and 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.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Begin a new page in the outprint. The page number is set to 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.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Set point size to scaled points (this is unit \$@ in GNU
troff). Classical troff used the unit points
(\$@ instead; see section COMPATIBILITY.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
-
- \)\$*
- Print a word, i.e., a sequence of characters 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
characters). This command is a groff extension; it is only used for
devices whose DESC file contains the tcommand keyword; see
groff_font(5).
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- 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 (an
integer in basic units \$@ This command is a groff
extension; it is only used for devices whose DESC file contains the
tcommand keyword; see groff_font(5).
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Move down to the absolute vertical position (a non-negative integer
in basic units \$@ relative to upper edge of current
page.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Move basic units \$@ down (n is a non-negative
integer). [CSTR #54] allows negative values for n
also, but groff doesn't use this.
- \f[B]\*[@arg1]\f[]\ \f[I]\,\*[@arg2]\/\f[]\$*
- Informs about a paddable whitespace to increase readability. The spacing
itself must be performed explicitly by a move command.
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 \$@ The arguments called \c $\*[@arg1] sub 1$,
$\*[@arg1] sub 2$, .\|.\|., $\*[@arg1] sub n$ \c \{\ \*[@arg1]1,
\*[@arg1]2, \&..., \*[@arg1]n stand for horizontal
distances where positive means right, negative left. The arguments called \c
$\*[@arg1] sub 1$, $\*[@arg1] sub 2$, .\|.\|., $\*[@arg1] sub n$ \c \{\
\*[@arg1]1, \*[@arg1]2, \&..., \*[@arg1]n 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. \
- \f[B]D\*[@sub]\f[]\ \*[@args]\|\*[@linebreak]
- Draw B-spline from current position to offset ($\*[@arg1] sub roman
\*[@index1]$,\ \c \{\ ($\*[@arg1] sub \*[@index1]$,\ \c $\*[@arg2] sub
roman \*[@index2]$)\$* \c \{\ $\*[@arg2] sub \*[@index2]$)\$* \c \{\
(\f[I]\*[@arg1]\*[@index1]\f[],\ \c \f[I]\*[@arg2]\*[@index2]\f[])\$* \c
then to offset ($\*[@arg1] sub roman \*[@index1]$,\ \c \{\ ($\*[@arg1] sub
\*[@index1]$,\ \c $\*[@arg2] sub roman \*[@index2]$)\$* \c \{\ $\*[@arg2]
sub \*[@index2]$)\$* \c \{\ (\f[I]\*[@arg1]\*[@index1]\f[],\ \c
\f[I]\*[@arg2]\*[@index2]\f[])\$* \c if given, etc. up to ($\*[@arg1] sub
roman \*[@index1]$,\ \c \{\ ($\*[@arg1] sub \*[@index1]$,\ \c $\*[@arg2]
sub roman \*[@index2]$)\$* \c \{\ $\*[@arg2] sub \*[@index2]$)\$* \c \{\
(\f[I]\*[@arg1]\*[@index1]\f[],\ \c \f[I]\*[@arg2]\*[@index2]\f[])\$* \c
This command takes a variable number of argument pairs; the current
position is moved to the terminal point of the drawn curve. \
- \f[B]Da\f[]\ \*[@args]\|\*[@linebreak]
- Draw arc from current position to ($\*[@arg1] sub roman \*[@index1]$,\ \c
\{\ ($\*[@arg1] sub \*[@index1]$,\ \c $\*[@arg2] sub roman
\*[@index2]$)\$* \c \{\ $\*[@arg2] sub \*[@index2]$)\$* \c \{\
(\f[I]\*[@arg1]\*[@index1]\f[],\ \c \f[I]\*[@arg2]\*[@index2]\f[])\$* \c
($\*[@arg1] sub roman \*[@index1]$,\ \c \{\ ($\*[@arg1] sub \*[@index1]$,\
\c $\*[@arg2] sub roman \*[@index2]$)\$* \c \{\ $\*[@arg2] sub
\*[@index2]$)\$* \c \{\ (\f[I]\*[@arg1]\*[@index1]\f[],\ \c
\f[I]\*[@arg2]\*[@index2]\f[])\$* \c with center at ($\*[@arg1] sub roman
\*[@index1]$,\ \c \{\ ($\*[@arg1] sub \*[@index1]$,\ \c $\*[@arg2] sub
roman \*[@index2]$)\$* \c \{\ $\*[@arg2] sub \*[@index2]$)\$* \c \{\
(\f[I]\*[@arg1]\*[@index1]\f[],\ \c \f[I]\*[@arg2]\*[@index2]\f[])\$* \c
then move the current position to the final point of the arc.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
-
- \)\$*
- Draw a solid circle using the current fill color with
diameter (integer in basic units \$@ 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.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Draw circle line with diameter (integer in basic
units \$@ with leftmost point at the current position; then
move the current position to the rightmost point of the circle.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Draw a solid ellipse in the current fill color with a horizontal diameter
of and a vertical diameter of (both integers in basic
units \$@ with the leftmost point at the current position;
then move to the rightmost point of the ellipse. This command is a
groff extension.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Draw an outlined ellipse with a horizontal diameter of and a
vertical diameter of (both integers in basic
units \$@ with the leftmost point at current position; then
move to the rightmost point of the ellipse.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- 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 corresponding
graphics commands). No position changing. This command is a groff
extension.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Set fill color for solid drawing objects using the CMY color scheme,
having the 3 color components cyan, magenta, and yellow.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Set fill color for solid drawing objects to the default fill color value
(black in most cases). No component arguments.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Set fill color for solid drawing objects to the shade of gray given by the
argument, an integer between 0 (black) and 65536 (white).
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Set fill color for solid drawing objects using the CMYK color scheme,
having the 4 color components cyan, magenta, yellow, and
black.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Set fill color for solid drawing objects using the RGB color scheme,
having the 3 color components red, green, and blue.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- The argument 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
No position changing. This command is a groff
extension.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Draw line from current position to offset (\f[I]\,\*[@arg1]\/\f[],\
\f[I]\,\*[@arg2]\/\f[])\$* (integers in basic units \$@ then
set current position to the end of the drawn line. \
- \f[B]D\*[@sub]\f[]\ \*[@args]\|\*[@linebreak]
- Draw a polygon line from current position to offset
(\f[I]\,\*[@arg1]\/\f[],\ \f[I]\,\*[@arg2]\/\f[])\$* from there to offset
(\f[I]\,\*[@arg1]\/\f[],\ \f[I]\,\*[@arg2]\/\f[])\$* etc. up to offset
(\f[I]\,\*[@arg1]\/\f[],\ \f[I]\,\*[@arg2]\/\f[])\$* 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. \
- \f[B]D\*[@sub]\f[]\ \*[@args]\|\*[@linebreak]
- 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.
- \f[B]D\*[@sub]\f[]\ \f[I]\,\$*\/\f[]\|\*[@linebreak]
- Set the current line thickness to (an integer in basic
units \$@ if if select the smallest available line
thickness; if 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.
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 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 section Separation.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Use 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.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Mount font position (a non-negative integer) with font
named (a text word), cf. groff_font(5).
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Set character height to (a positive integer in scaled
points \$@ Classical troff used the unit points
(\$@ instead; see section COMPATIBILITY.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Initialize device. This is the third command of the prologue.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Parsed but ignored. The classical documentation reads pause device, can
be restarted.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Resolution is while is the minimal horizontal motion, and the minimal
vertical motion possible with this device; all arguments are positive
integers in basic units \$@ per inch. This is the second
command of the prologue.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Set slant to degrees (an integer in basic
units \$@
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Terminates the processing of the current file; issued as the last command of
any intermediate troff output.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Generate trailer information, if any. In groff, this is actually just
ignored.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Set name of device to word 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.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Configure underlining of spaces. If is 1, start underlining of
spaces; if 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.
- \f[B]x\*[@sub]\f[]\*[@args]\f[]\|\*[@linebreak]
- (\$1 control command)
Send string 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, the writing of a single character was mostly
done by a very strange command 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.
- Move right
- (exactly two decimal digits) basic units \$@ then print
character
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 characters 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.
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 hell world
fed into groff on the command line.
- \[bu]
- High-resolution device ps
shell>\h'1m'\f[CB]\$*\f[]\/
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.
- \[bu]
- 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>\h'1m'\f[CB]\$*\f[]\/
# 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.
- \[bu]
- 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>\h'1m'\f[CB]\$*\f[]\/
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.
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.
- \[bu]
- The classical quasi device independence is not yet implemented.
- \[bu]
- 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.
- \[bu]
- 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.
- \[bu]
- The argument of the commands s and x H has the implicit unit
scaled point \$@ in groff, while classical
troff had point (\$@ 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.
- \[bu]
- 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).
- /usr/share/groff_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
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 prompt
shell>\h'1m'\f[CB]\$*\f[]\/
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>\h'1m'\f[CB]\$*\f[]\/
The classical troff output language is described in two
AT&T Bell Labs CSTR documents available on-line at
- [CSTR #97]
- A Typesetter-independent TROFF by Brian Kernighan is the
original and most concise documentation on the output language; see
- [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
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
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 has been rewritten 2002 by Bernd Warken and is maintained
by