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           This  manual  page  describes the intermediate output format of the GNU
           roff(7) text processing system.  This output is produced by  a  run  of
           the  GNU  troff(1) program before it is fed into a device postprocessor
           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  sys-
           tem.   The groff program provides the option -Z to inhibit postprocess-
           ing, 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 post-
           processors.  This parser is smarter on whitespace and implements  obso-
           lete  elements  for compatibility, otherwise both formats are the same.
           The pre-groff roff versions are denoted as classical troff.
           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  com-
           pletely different from the groff(7) language.  While the groff language
           is a high-level programming language for text processing, the  interme-
           diate  output  language  is  a  kind of low-level assembler language by
           specifying all positions on the page for writing and drawing.
           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 informa-
           tion 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 doc-
           ument, the term "command" always refers to the intermediate output lan-
           guage,  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  syntac-
           tical space.  It separates commands and arguments, but is only required
           the parser allows to stack such commands on the same line,  but  fortu-
           nately,  in  groff intermediate output, every command with at least one
           argument is followed by a line break, thus  providing  excellent  read-
           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
           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 val-
           ues 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 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  com-
       Document Parts
           A  correct intermediate output document consists of two parts, the pro-
           logue 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
           to the current page, all other positioning is done relative to the cur-
           rent location within this page.


           This  section describes all intermediate output commands, the classical
           commands as well as the groff extensions.
       Comment Command
                  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  inte-
           ger  arguments  would  clash  or  if the preceding argument ends with a
           string argument.
           C xxx<white_space>
                  Print a special groff character named xxx.  The trailing syntac-
                  tical  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.
           c c    Print character c at the current print position; the character's
                  size  is  read  from  the  font file.  The print position is not
           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.   [54]  allows negative values for n also, but groff
                  doesn't use this.
           m color_scheme [component ...]
                  Set the color for text (glyphs), line drawing, and  the  outline
                  of graphic objects using different color schemes; the analoguous
                  command for the filling color of graphic  objects  is  DF.   The
                         Set  color to the shade of gray given by the argument, an
                         integer between 0 (black) and 65536 (white).
                  mk cyan magenta yellow black
                         Set color using the CMYK color scheme, having the 4 color
                         components cyan, magenta, yellow, and black.
                  mr red green blue
                         Set  color using the RGB color scheme, having the 3 color
                         components red, green, and blue.
           N n    Print character with index n (a  non-negative  integer)  of  the
                  current  font.  The print position is not changed.  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 per-
                  forming 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
           t xxx<white_space>
           t xxx dummy_arg<white_space>
                  Print a word, i.e. a sequence of characters xxx terminated by  a
                  space  character  or  a  line  break; an optional second integer
                  argument is ignored (this allows the formatter  to  generate  an
                  even  number  of  arguments).   The  first  character  should be
                  printed at the current position, the current horizontal position
                  should  then  be  increased by the width of the first character,
                  and so on for each character.  The widths of the characters  are
                  read  from the font file, scaled for the current point size, and
                  rounded to a multiple of  the  horizontal  resolution.   Special
                  characters  cannot be printed using this command (use the C com-
                  mand for named characters).  This command is a groff  extension;
                  it  is  only used for devices whose DESC file contains the tcom-
                  mand keyword; see groff_font(5).
           u n xxx<white_space>
                  Print word with track kerning.  This is the same as the  t  com-
                  mand except that after printing each character, the current hor-
       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 subcom-
           mand; this is followed by a fixed or variable number of  integer  argu-
           ments  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  com-
           ment), so each D command is terminated by a syntactical line break.
           troff output follows the classical spacing rules (no space between com-
           mand and subcommand, all arguments are preceded by a single space char-
           acter),  but  the parser allows optional space between the command let-
           ters 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  arguments called h1, h2, ..., hn h1, h2, ..., hn stand
           for horizontal distances where positive  means  right,  negative  left.
           The arguments called v1, v2, ..., vn v1, v2, ..., vn stand for vertical
           distances where positive means down, negative up.  All these  distances
           are offsets relative to the current location.
           Unless  indicated otherwise, each graphics command directly corresponds
           to a similar groff \D escape sequence; see groff(7).
           Unknown D commands are assumed to be  device-specific.   Its  arguments
           are  parsed as strings; the whole information is then sent to the post-
           In the following command reference,  the  syntax  element  <line_break>
           means a syntactical line break as defined in section Separation.
           D~ h1 v1 h2 v2 ... hn vn<line_break>
                  Draw  B-spline from current position to offset (h1, v1), then to
                  offset (h2, v2) if given, etc.  up  to  (hn, vn).  This  command
                  takes  a variable number of argument pairs; the current position
                  is moved to the terminal point of the drawn curve.
           Da h1 v1 h2 v2<line_break>
                  Draw arc from current position to (h1, v1)+(h2, v2) with  center
                  at  (h1, v1);  then move the current position to the final point
                  of the arc.
           DC d<line_break>
           DC d dummy_arg<line_break>
                  Draw a solid circle using the current fill color with diameter d
                  (integer  in  basic  units u) with leftmost point at the current
                  position; then move the current position to the rightmost  point
                  of  the  circle.  An optional second integer argument is ignored
                  (this allows to the formatter to  generate  an  even  number  of
           De h v<line_break>
                  Draw  an  outlined ellipse with a horizontal diameter of h and a
                  vertical diameter of v (both integers in basic units u) with the
                  leftmost  point  at current position; then move to the rightmost
                  point of the ellipse.
           DF color_scheme [component ...]<line_break>
                  Set fill color for solid drawing objects using  different  color
                  schemes;  the  analoguous command for setting the color of text,
                  line graphics, and the outline of graphic  objects  is  m.   The
                  color  components  are  specified as integer arguments between 0
                  and 65536.  The number of color  components  and  their  meaning
                  vary for the different color schemes.  These commands are gener-
                  ated 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
                  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
           Dp h1 v1 h2 v2 ... hn vn<line_break>
                  Draw  a  polygon  line from current position to offset (h1, v1),
                  from there to offset (h2, v2), etc. up to offset  (hn, vn),  and
                  from  there  back to the starting position.  For historical rea-
                  sons, 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 exten-
           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  posi-
                  tion, 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 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  readabil-
           ity, it can be written as a word, i.e. an arbitrary sequence of charac-
           ters 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  com-
           In  the  following, the syntax element <line_break> means a syntactical
           line break as defined in section Separation.
           xF name<line_break>
                  (Filename control command)
                  Use name as the intended name for  the  current  file  in  error
                  reports.   This is useful for remembering the original file name
                  (init control command)
                  Initialize device.  This is the third command of the prologue.
                  (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 argu-
                  ments 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 (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.
           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  other-
                  wise.  This command is a groff extension.
           xX anything<line_break>
                  (X-escape control command)
                  Send  string  anything uninterpreted to the device.  If the line
                  following this command starts with a + character  this  line  is
                  interpreted  as a continuation line in the following sense.  The
                  + is ignored, but a newline character is  sent  instead  to  the
                  device,  the  rest  of the line is sent uninterpreted.  The same
                  applies to all following lines until the first  character  of  a
                  In groff, arbitrary syntactical space  around  and  within  this
                  command  is  allowed to be added.  Only when a preceding command
                  on the same line ends with an argument of variable length a sep-
                  arating 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  sys-
           tem  provides powerful means that make the programming of such postpro-
           cessors 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 refer-
           ence 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.
           ? High-resolution device ps
             shell> echo hell world | groff -Z -T ps
             x T ps
             x res 72000 1 1
             x init
             x font 5 TR
             n12000 0
             x trailer
             # prologue
             x T latin1
             x res 240 24 40
             x init
             # begin a new page
             # font setup
             x font 1 R
             # initial positioning on the page
             # write text 'hell'
             # inform about a space, and do it by a horizontal jump
             # write text 'world'
             # announce line break, but do nothing because ...
             n40 0
             # ... the end of the document has been reached
             x trailer
             x 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> echo hell world | groff -Z -T X100
             x T X100
             x res 100 1 1
             x init
             x font 5 TR
             # write text with old-style jump-and-write command
             n16 0
             x trailer
           ? The  old  hardware was very different from what we use today.  So the
             groff devices are also fundamentally different from the ones in clas-
             sical 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 imple-
             menting 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 out-
             put 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  classi-
             cal  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 compat-
             ibility reasons.
           The differences between groff and classical  troff  are  documented  in


                  Device description file for device name.
                  Defines  the  parser and postprocessor for the intermediate out-
                  put.  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  sec-
           tion 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).
                  option -Z and further readings on groff.
                  The differences between the intermediate  output  in  groff  and
                  classical troff.
           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 doc-
           ument, see the groff info file.  It can be read within  the  integrated
           help systems, within emacs(1) or from the shell prompt by
                  shell> info groff
           The  classical troff output language is described in two AT&T Bell Labs
           CSTR documents available  on-line  at  Bell  Labs  CSTR  site  <http://
           [CSTR #97]
                  A  Typesetter-independent TROFF by Brian Kernighan is the origi-
                  nal and most concise documentation on the output  language;  see
                  CSTR #97 <>.
           [CSTR #54]
                  The  1992  revision  of  the  Nroff/Troff User's Manual by J. F.
                  Osanna and Brian  Kernighan  isn't  as  concise  as  [CSTR  #97]
                  regarding   the   output   language;   see   CSTR  #54  <http://


           Copyright (C) 1989, 2001, 2002 Free Software Foundation, Inc.
           This document is distributed under the terms of the FDL (GNU Free Docu-
           mentation  License)  version  1.1 or later.  You should have received a
           copy of the FDL with this package; it is also available on-line at  the
           GNU copyleft site <>.
           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
           Werner Lemberg <>.

    Groff Version 12 September 2002 GROFF_OUT(5)


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