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           This  manual page describes the language differences between groff, the
           GNU roff text processing system and the classical roff formatter of the
           freely  available  Unix  7 of the 1970s, documented in the Troff User's
           Manual by Osanna and Kernighan.  This inludes the roff language as well
           as the intermediate output format (troff output).
           The  section SEE ALSO gives pointers to both the classical roff and the
           modern groff documentation.
           At the moment, this document is the place of the most actual documenta-
           tion  within the groff system.  This might change in the future.  Actu-
           ally, all novelties of the groff language are first described here  and
           will pervade into the other documents only at a later stage.


           In this section, all additional features of groff compared to the clas-
           sical Unix 7 troff are described in detail.
       Long names
           The names of number registers, fonts,  strings/macros/diversions,  spe-
           cial characters, and colors can be of any length.  In escape sequences,
           additionally to the classical (xx  construction  for  a  two  character
           name, you can use [xxx] for a name of arbitrary length, for example in
           \[xxx]    Print the special character called xxx.
           \f[xxx]   Set  font  xxx.   Additionally, \f[] is a new syntax equal to
                     \fP, i.e., to return to the previous font.
           \*[xxx arg1 arg2 ...]
                     Interpolate string xxx, taking arg1, arg2, ... as  arguments.
           \n[xxx]   Interpolate number register xxx.
       Fractional pointsizes
           A scaled point is equal to 1/sizescale points, where sizescale is spec-
           ified in the DESC file (1 by default).  There is a new scale  indicator
           z that has the effect of multiplying by sizescale.  Requests and escape
           sequences in troff interpret arguments that represent  a  pointsize  as
           being  in  units of scaled points, but they evaluate each such argument
           using a default scale indicator of z.  Arguments treated  in  this  way
           are  the  argument  to  the  ps  request,  the third argument to the cs
           request, the second and fourth arguments to the tkf request, the  argu-
           ment  to  the  \H  escape sequence, and those variants of the \s escape
           sequence that take a numeric expression as their argument.
           For example, suppose sizescale is 1000; then a  scaled  point  will  be
           equivalent  to  a  millipoint;  the  call  .ps 10.25  is  equivalent to
           .ps 10.25z and so sets the pointsize to 10250 scaled points,  which  is
           equal to 10.25 points.
       Numeric expressions
           Spaces are permitted in a number expression within parentheses.
           M  indicates  a scale of 100ths of an em.  f indicates a scale of 65536
           units, providing fractions for  color  definitions  with  the  defcolor
           request.  For example, 0.5f = 32768u.
           e1>?e2 The maximum of e1 and e2.
           e1<?e2 The minimum of e1 and e2.
           (c;e)  Evaluate  e  using  c as the default scaling indicator.  If c is
                  missing, ignore scaling indicators in the evaluation of e.
       New escape sequences
                  This expands to 1 or 0 resp., depending on whether  anything  is
                  or  is not acceptable as the name of a string, macro, diversion,
                  number register, environment, font, or color.  It will return  0
                  if anything is empty.  This is useful if you want to lookup user
                  input in some sort of associative table.
                  This expands to 1 or 0 resp., depending on whether  anything  is
                  or  is not a valid numeric expression.  It will return 0 if any-
                  thing is empty.
                  Typeset character named xxx.  Normally it is more convenient  to
                  use \[xxx].  But \C has the advantage that it is compatible with
                  recent versions of UNIX and is available in compatibility  mode.
           \E     This  is equivalent to an escape character, but it is not inter-
                  preted in copy-mode.  For example,  strings  to  start  and  end
                  superscripting could be defined like this
                         .ds { \v'-.3m'\s'\En[.s]*6u/10u'
                         .ds } \s0\v'.3m'
                  The  use  of \E ensures that these definitions will work even if
                  \*{ gets interpreted in copy-mode (for example, by being used in
                  a macro argument).
                  Change  font family.  This is the same as the fam request.  \F[]
                  switches back to the previous color (note that \FP  won't  work;
                  it selects font family 'P' instead).
                  the char request, for example
                         .char \[phone] \f(ZD\N'37'
                  The  code of each character is given in the fourth column in the
                  font description file after the charset command.  It is possible
                  to  include  unnamed  characters in the font description file by
                  using a name of ---; the \N escape sequence is the only  way  to
                  use these.
           \O[n]  Suppressing  troff  output.   The escapes \02, \O3, \O4, and \O5
                  are intended for internal use by grohtml.
                  \O0    Disable any ditroff glyphs  from  being  emitted  to  the
                         device  driver,  provided  that  the escape occurs at the
                         outer level (see \O3 and \O4).
                  \O1    Enable output of glyphs, provided that the escape  occurs
                         at the outer level.
                         \O0   and   \O1  also  reset  the  registers  \n[opminx],
                         \n[opminy], \n[opmaxx], and \n[opmaxy] to -1.  These four
                         registers mark the top left and bottom right hand corners
                         of a box which encompasses all written glyphs.
                  \O2    Provided that the  escape  occurs  at  the  outer  level,
                         enable  output of glyphs and also write out to stderr the
                         page number and four registers  encompassing  the  glyphs
                         previously written since the last call to \O.
                  \O3    Begin  a  nesting  level.  At start-up, troff is at outer
                         level.  This is really an internal mechanism for  grohtml
                         while  producing  images.   They are generated by running
                         the troff source through troff to the  postscript  device
                         and ghostscript to produce images in PNG format.  The \O3
                         escape will start a new page if the device  is  not  html
                         (to  reduce  the  possibility  of  images crossing a page
                  \O4    End a nesting level.
                         This escape is  grohtml  specific.   Provided  that  this
                         escape  occurs at the outer nesting level, write filename
                         to stderr.  The position of the image, P, must be  speci-
                         fied  and must be one of l, r, c, or i (left, right, cen-
                         tered, inline).  filename will  be  associated  with  the
                         production of the next inline image.
           \R'name ?n'
                  This has the same effect as
                  Interpolate  the  contents  of  the environment variable xxx, as
                  returned by getenv(3).  \V is interpreted in copy-mode.
                  This is approximately equivalent to  \X'\*[xxx]'.   However  the
                  contents of the string or macro xxx are not interpreted; also it
                  is permitted for xxx to have been defined as a  macro  and  thus
                  contain  newlines (it is not permitted for the argument to \X to
                  contain newlines).  The inclusion of newlines requires an exten-
                  sion  to  the UNIX troff output format, and will confuse drivers
                  that do not know about this extension.
                  Print anything and then  restore  the  horizontal  and  vertical
                  position; anything may not contain tabs or leaders.
           \$0    The  name  by  which  the  current  macro  was invoked.  The als
                  request can make a macro have more than one name.
           \$*    In a macro or string, the concatenation  of  all  the  arguments
                  separated by spaces.
           \$@    In  a  macro  or  string, the concatenation of all the arguments
                  with each surrounded by double quotes, and separated by  spaces.
                  In  a  macro or string, this gives the nn-th or nnn-th argument.
                  Macros and strings can have an unlimited number of arguments.
                  When used in a diversion, this will transparently embed anything
                  in  the  diversion.   anything  is  read in copy mode.  When the
                  diversion is reread, anything will be interpreted.  anything may
                  not  contain newlines; use \! if you want to embed newlines in a
                  diversion.  The escape sequence \? is also  recognised  in  copy
                  mode  and  turned  into  a single internal code; it is this code
                  that terminates anything.  Thus
                         .nr x 1
                         .di d
                         .nr x 2
                         .di e
                         .nr x 3
           \,     This modifies the spacing of the following character so that the
                  spacing between that character and the preceding character  will
                  correct  if the preceding character is a roman character.  It is
                  a good idea to use this escape sequence whenever a roman charac-
                  ter  is  immediately followed by an italic character without any
                  intervening space.
           \)     Like \& except that it behaves like a  character  declared  with
                  the cflags request to be transparent for the purposes of end-of-
                  sentence recognition.
           \~     This produces an unbreakable space that stretches like a  normal
                  inter-word space when a line is adjusted.
           \:     This  causes  the  insertion of a zero-width break point.  It is
                  equal to \% within a word but without insertion of a soft hyphen
           \#     Everything  up  to  and  including  the next newline is ignored.
                  This is interpreted in copy mode.  It is like \" except that  \"
                  does not ignore the terminating newline.
       New requests
           .aln xx yy
                  Create an alias xx for number register object named yy.  The new
                  name and the old name will be  exactly  equivalent.   If  yy  is
                  undefined,  a  warning  of  type  reg will be generated, and the
                  request will be ignored.
           .als xx yy
                  Create an alias xx for  request,  string,  macro,  or  diversion
                  object  named yy.  The new name and the old name will be exactly
                  equivalent (it is similar to a hard rather than  a  soft  link).
                  If yy is undefined, a warning of type mac will be generated, and
                  the request will be ignored.  The de, am, di,  da,  ds,  and  as
                  requests  only  create  a  new  object if the name of the macro,
                  diversion or string diversion is currently undefined or if it is
                  defined  to  be  a request; normally they modify the value of an
                  existing object.
           .ami xx yy
                  Append to macro indirectly.  See the dei request below for  more
           .am1 xx yy
                  Similar  to  .am,  but compatibility mode is switched off during
                  execution.  To be more precise, a 'compatibility save' token  is
                  inserted at the beginning of the macro addition, and a 'compati-
                  bility restore'  token  at  the  end.   As  a  consequence,  the
                  requests am, am1, de, and de1 can be intermixed freely since the
                  compatibility save/restore tokens only affect  the  macro  parts
                         .tr @@
                         .asciify x
                  will set register n to 1.  Note that  glyph  information  (font,
                  font size, etc.) is not preserved; use .unformat instead.
           .as1 xx yy
                  Similar  to  .as,  but compatibility mode is switched off during
                  expansion.  To be more precise, a 'compatibility save' token  is
                  inserted  at  the  beginning of the string, and a 'compatibility
                  restore' token at the end.  As a consequence, the  requests  as,
                  as1,  ds, and ds1 can be intermixed freely since the compatibil-
                  ity save/restore tokens only affect the (sub)strings defined  by
                  as1 and ds1.
                  Print a backtrace of the input stack on stderr.
           .blm xx
                  Set the blank line macro to xx.  If there is a blank line macro,
                  it will be invoked when a blank line is encountered  instead  of
                  the usual troff behaviour.
           .box xx
           .boxa xx
                  These  requests  are  similar to the di and da requests with the
                  exception that a partially filled line will not become  part  of
                  the  diversion  (i.e.,  the  diversion  always starts with a new
                  line) but restored after ending the  diversion,  discarding  the
                  partially filled line which possibly comes from the diversion.
           .break Break  out  of  a  while  loop.  See also the while and continue
                  requests.  Be sure not to confuse this with the br request.
           .brp   This is the same as \p.
           .cflags n c1 c2...
                  Characters c1, c2,... have properties determined by n, which  is
                  ORed from the following:
                  1      The  character  ends  sentences (initially characters .?!
                         have this property).
                  2      Lines can be broken before the  character  (initially  no
                         characters have this property); a line will not be broken
                         at a character with this property unless  the  characters
                         on each side both have non-zero hyphenation codes.
                  4      Lines  can be broken after the character (initially char-
                         acters -\(hy\(em have this property); a line will not  be
                         ing a zero space  factor  in  TeX  (initially  characters
                         "')]*\(dg\(rq have this property).
           .char c string
                  Define  character  c to be string.  Every time character c needs
                  to be printed, string will be processed in a temporary  environ-
                  ment  and  the  result  will be wrapped up into a single object.
                  Compatibility mode will be turned off and the  escape  character
                  will be set to \ while string is being processed.  Any embolden-
                  ing, constant spacing or track kerning will be applied  to  this
                  object rather than to individual characters in string.
                  A character defined by this request can be used just like a nor-
                  mal character provided by  the  output  device.   In  particular
                  other characters can be translated to it with the tr request; it
                  can be made the leader character by  the  lc  request;  repeated
                  patterns  can  be  drawn  with the character using the \l and \L
                  escape sequences; words containing the character can be  hyphen-
                  ated correctly, if the hcode request is used to give the charac-
                  ter a hyphenation code.
                  There is a special  anti-recursion  feature:  use  of  character
                  within  the  character's  definition will be handled like normal
                  characters not defined with char.
                  A character definition can be removed with the rchar request.
           .chop xx
                  Chop the last character off  macro,  string,  or  diversion  xx.
                  This  is  useful for removing the newline from the end of diver-
                  sions that are to be interpolated as strings.
           .close stream
                  Close the stream named stream;  stream  will  no  longer  be  an
                  acceptable argument to the write request.  See the open request.
                  Finish the current iteration of a  while  loop.   See  also  the
                  while and break requests.
           .color n
                  If  n  is  non-zero  or  missing,  enable  colors  (this  is the
                  default), otherwise disable them.
           .cp n  If n is non-zero or missing, enable compatibility  mode,  other-
                  wise  disable  it.   In  compatibility  mode, long names are not
                  recognised, and the incompatibilities caused by  long  names  do
                  not arise.
           .defcolor xxx scheme color_components
                  Define  color.   scheme  can be one of the following values: rgb
                  (three components), cym (three components),  cmyk  (four  compo-
                  request, thus the above statement is equivalent to
                         .defcolor darkgreen rgb 0.1 0.5 0.2
                  The color named default  (which  is  device-specific)  can't  be
                  redefined.   It is possible that the default color for \M and \m
                  is not the same.
           .dei xx yy
                  Define macro indirectly.  The following example
                         .ds xx aa
                         .ds yy bb
                         .dei xx yy
                  is equivalent to
                         .de aa bb
           .de1 xx yy
                  Similar to .de, but compatibility mode is  switched  off  during
                  execution.   On  entry,  the current compatibility mode is saved
                  and restored at exit.
           .do xxx
                  Interpret .xxx with compatibility mode disabled.  For example,
                         .do fam T
                  would have the same effect as
                         .fam T
                  except that it would work even if compatibility  mode  had  been
                  enabled.   Note that the previous compatibility mode is restored
                  before any files sourced by xxx are interpreted.
           .ds1 xx yy
                  Similar to .ds, but compatibility mode is  switched  off  during
                  expansion.   To be more precise, a 'compatibility save' token is
                  inserted at the beginning of the string,  and  a  'compatibility
                  restore' token at the end.
           .ecs   Save current escape character.
           .ecr   Restore  escape  character  saved  with ecs.  Without a previous
                  call to ecs, '\' will be the new escape character.
           .evc xx
                  Copy the contents of environment xx to the current  environment.
                  No pushing or popping of environments will be done.
           .fspecial f s1 s2...
                  When the current font is f, fonts s1, s2,...  will  be  special,
                  that  is,  they  will searched for characters not in the current
                  font.  Any fonts  specified  in  the  special  request  will  be
                  searched after fonts specified in the fspecial request.
           .ftr f g
                  Translate  font  f to g.  Whenever a font named f is referred to
                  in an \f escape sequence, or in the ft, ul, bd,  cs,  tkf,  spe-
                  cial,  fspecial, fp, or sty requests, font g will be used.  If g
                  is missing, or equal to f then font f will not be translated.
           .hcode c1 code1 c2 code2...
                  Set the hyphenation code of character c1 to code1 and that of c2
                  to  code2.   A hyphenation code must be a single input character
                  (not a special character) other than a digit or a  space.   Ini-
                  tially  each lower-case letter a-z has a hyphenation code, which
                  is itself, and each upper-case letter A-Z has a hyphenation code
                  which  is  the  lower-case  version of itself.  See also the hpf
           .hla lang
                  Set the  current  hyphenation  language  to  lang.   Hyphenation
                  exceptions  specified  with  the hw request and hyphenation pat-
                  terns specified with the hpf request are  both  associated  with
                  the  current  hyphenation  language.  The hla request is usually
                  invoked by the troffrc file.
           .hlm n Set the maximum number of consecutive hyphenated lines to n.  If
                  n  is  negative,  there is no maximum.  The default value is -1.
                  This value is associated with  the  current  environment.   Only
                  lines output from an environment count towards the maximum asso-
                  ciated with that environment.  Hyphens  resulting  from  \%  are
                  counted; explicit hyphens are not.
           .hpf file
                  Read  hyphenation  patterns from file; this will be searched for
                  in the same way that name.tmac is searched for when  the  -mname
                  option is specified.  It should have the same format as (simple)
                  TeX patterns files.  More specifically, the  following  scanning
                  rules are implemented.
                  ?      A  percent  sign  starts  a comment (up to the end of the
                         line) even if preceded by a backslash.
                  ?      No support for 'digraphs' like \$.
                  ?      ^^xx (x is 0-9 or a-f) and ^^x (character code  of  x  in
                         the range 0-127) are recognized; other use of ^ causes an
                         (only recognizing the % character as the start of a  com-
                  Use  the hpfcode request to map the encoding used in hyphenation
                  patterns files to groff's input encoding.
                  The set of hyphenation patterns is associated with  the  current
                  language  set  by  the  hla request.  The hpf request is usually
                  invoked by the troffrc file; a second call replaces the old pat-
                  terns with the new ones.
           .hpfa file
                  The  same  as hpf except that the hyphenation patterns from file
                  are appended to the patterns already loaded in the current  lan-
           .hpfcode a b c d ...
                  After  reading  a hyphenation patterns file with the hpf or hpfa
                  request, convert all characters with character  code  a  in  the
                  recently  read  patterns  to  character code b, character code c
                  to d, etc.  Initially, all character codes  map  to  themselves.
                  The arguments of hpfcode must be integers in the range 0 to 255.
                  Note that it is even possible to use character codes  which  are
                  invalid in groff otherwise.
           .hym n Set  the  hyphenation  margin  to n: when the current adjustment
                  mode is not b, the line will not be hyphenated if the line is no
                  more  than  n  short.  The default hyphenation margin is 0.  The
                  default scaling indicator for this request is  m.   The  hyphen-
                  ation  margin  is  associated with the current environment.  The
                  current hyphenation margin is available in the  \n[.hym]  regis-
           .hys n Set the hyphenation space to n: when the current adjustment mode
                  is b don't hyphenate the line if the line can  be  justified  by
                  adding  no  more  than  n  extra  space to each word space.  The
                  default hyphenation space is 0.  The default  scaling  indicator
                  for this request is m.  The hyphenation space is associated with
                  the current  environment.   The  current  hyphenation  space  is
                  available in the \n[.hys] register.
           .itc n macro
                  Variant  of  .it  for which a line interrupted with \c counts as
                  one input line.
           .kern n
                  If n is non-zero or missing, enable pairwise kerning,  otherwise
                  disable it.
           .length xx string
                  Compute  the length of string and return it in the number regis-
                  ter xx (which is not necessarily defined before).
                         a         b         c
                  In line-tabs mode, the same code gives
                         a         b                   c
                  Line-tabs mode is associated with the current  environment;  the
                  read-only  number register \n[.linetabs] is set to 1 if in line-
                  tabs mode, and 0 otherwise.
           .mso file
                  The same as the so request except that file is searched  for  in
                  the  same directories as macro files for the the -m command line
                  option.  If the file name to be included has the form  name.tmac
                  and  it  isn't found, mso tries to include instead and
                  vice versa.
           .nop anything
                  Execute anything.  This is similar to '.if 1'.
           .nroff Make the n built-in condition true and the t built-in  condition
                  false.  This can be reversed using the troff request.
           .open stream filename
                  Open  filename for writing and associate the stream named stream
                  with it.  See also the close and write requests.
           .opena stream filename
                  Like open, but if filename exists, append to it instead of trun-
                  cating it.
           .output string
                  Emit  string  directly  to  the  intermediate output (subject to
                  copy-mode interpretation); this is similar to \!   used  at  the
                  top level.  An initial double quote in string is stripped off to
                  allow initial blanks.
           .pnr   Print the names and contents of  all  currently  defined  number
                  registers on stderr.
           .psbb filename
                  Get  the bounding box of a PostScript image filename.  This file
                  must conform to Adobe's Document  Structuring  Conventions;  the
                  command  looks for a %%BoundingBox comment to extract the bound-
                  ing box values.  After a successful call,  the  coordinates  (in
                  PostScript  units)  of the lower left and upper right corner can
                  be  found  in  the  registers  \n[llx],  \n[lly],  \n[urx],  and
                  \n[ury],  respectively.   If  some  error has occurred, the four
                  output.  With no argument, the post-vertical line space  is  set
                  to its previous value.
                  The total vertical line spacing consists of four components: .vs
                  and \x with a negative value which are applied before  the  line
                  is  output,  and  .pvs  and  \x  with a positive value which are
                  applied after the line is output.
           .rchar c1 c2...
                  Remove the definitions of characters c1, c2,...  This undoes the
                  effect of a char request.
                  Within a macro, return immediately.  No effect otherwise.
           .rj n  Right justify the next n input lines.  Without an argument right
                  justify the next input line.  The number of lines  to  be  right
                  justified is available in the \n[.rj] register.  This implicitly
                  does .ce 0.  The ce request implicitly does .rj 0.
           .rnn xx yy
                  Rename number register xx to yy.
           .shc c Set the soft hyphen character to c.  If c is omitted,  the  soft
                  hyphen  character  will  be  set  to the default \(hy.  The soft
                  hyphen character is the character which will be inserted when  a
                  word  is hyphenated at a line break.  If the soft hyphen charac-
                  ter does not exist in the font of the character immediately pre-
                  ceding a potential break point, then the line will not be broken
                  at that point.  Neither definitions  (specified  with  the  char
                  request)  nor  translations  (specified with the tr request) are
                  considered when finding the soft hyphen character.
           .shift n
                  In a macro, shift the  arguments  by  n  positions:  argument  i
                  becomes  argument  i-n;  arguments  1  to  n  will  no longer be
                  available.  If n is missing, arguments will  be  shifted  by  1.
                  Shifting by negative amounts is currently undefined.
           .sizes s1 [0]
                  This command is similar to the sizes command of a DESC file.  It
                  sets the available font  sizes  for  the  current  font  to  s1,
                  s2,...,  sn  scaled points.  The list of sizes can be terminated
                  by an optional 0.  Each si can also be a  range  of  sizes  m-n.
                  Contrary  to  the  font file command, the list can't extend over
                  more than a single line.
           .special s1 s2...
                  Fonts s1, s2, are special and will be  searched  for  characters
                  not in the current font.
                  is  the index of a font position and so is also either a font or
                  a style.  When it is a style, the font that is actually used  is
                  the  font  the name of which is the concatenation of the name of
                  the current family and the name of the current style.  For exam-
                  ple,  if the current font is 1 and font position 1 is associated
                  with style R and the current font family is T, then font TR will
                  be  used.   If the current font is not a style, then the current
                  family is ignored.  When the requests cs, bd, tkf, uf, or  fspe-
                  cial  are  applied to a style, then they will instead be applied
                  to the member of the current family corresponding to that style.
                  The  default  family  can be set with the -f option.  The styles
                  command in the DESC file controls which font positions (if  any)
                  are initially associated with styles rather than fonts.
           .substring xx n1 [n2]
                  Replace  the  string  named xx with the substring defined by the
                  indices n1 and n2.   The  first  character  in  the  string  has
                  index  0.   If  n2  is  omitted,  it is taken to be equal to the
                  string's length.  If the index value n1 or n2  is  negative,  it
                  will be counted from the end of the string, going backwards: The
                  last character has index -1, the character before the last char-
                  acter has index -2, etc.
           .tkf f s1 n1 s2 n2
                  Enable track kerning for font f.  When the current font is f the
                  width of every character will be increased by an amount  between
                  n1  and n2; when the current point size is less than or equal to
                  s1 the width will be increased by n1; when it is greater than or
                  equal  to  s2  the width will be increased by n2; when the point
                  size is greater than or equal to s1 and less than or equal to s2
                  the increase in width is a linear function of the point size.
           .tm1 string
                  Similar to the tm request, string is read in copy mode and writ-
                  ten on the standard error, but an initial double quote in string
                  is stripped off to allow initial blanks.
           .tmc string
                  Similar to tm1 but without writing a final newline.
           .trf filename
                  Transparently  output  the contents of file filename.  Each line
                  is output as if preceded by \!; however, the lines are not  sub-
                  ject to copy-mode interpretation.  If the file does not end with
                  a newline, then a newline will be added.  For example,  you  can
                  define a macro x containing the contents of file f, using
                         .di x
                         .trf f
                  Unlike  with  the cf request, the file cannot contain characters
                         .asciify xxx
                  The result is x a.  Using tr, the result would be x x.
           .trnt abcd
                  This is the same as the tr request except that the  translations
                  do  not  apply  to  text that is transparently throughput into a
                  diversion with \!.  For example,
                         .tr ab
                         .di x
                         \!.tm a
                  will print b; if trnt is used instead of tr it will print a.
           .troff Make the n built-in condition false, and the t  built-in  condi-
                  tion true.  This undoes the effect of the nroff request.
           .unformat xx
                  This  request  'unformats'  the  diversion  xx.  Contrary to the
                  .asciify request, which tries to convert formatted  elements  of
                  the  diversion back to input tokens as much as possible, .unfor-
                  mat will only handle tabs  and  spaces  between  words  (usually
                  caused  by spaces or newlines in the input) specially.  The for-
                  mer are treated as if they were input tokens, and the latter are
                  stretchable  again.  Note that the vertical size of lines is not
                  preserved.  Glyph information (font,  font  size,  space  width,
                  etc.)  is  retained.   Useful  in  conjunction with the .box and
                  .boxa requests.
           .vpt n Enable vertical position traps if n is  non-zero,  disable  them
                  otherwise.   Vertical  position traps are traps set by the wh or
                  dt requests.  Traps set by the it request are not vertical posi-
                  tion  traps.  The parameter that controls whether vertical posi-
                  tion traps are enabled is global.  Initially  vertical  position
                  traps are enabled.
           .warn n
                  Control  warnings.   n is the sum of the numbers associated with
                  each warning that is to be enabled; all other warnings  will  be
                  disabled.   The number associated with each warning is listed in
                  troff(1).  For example, .warn 0 will disable all  warnings,  and
                  .warn  1  will  disable  all  warnings except that about missing
                  characters.  If n is not given, all warnings will be enabled.
           .warnscale si
                  Set the scaling indicator used in warnings to si.  Valid  values
                  for si are u, i, c, p, and P.  At startup, it is set to i.
           .writem stream xx
                  Write the contents of the macro or string xx to the stream named
                  stream.  stream must previously have been the subject of an open
                  request.  xx is read in copy mode.
       Extended requests
           .cf filename
                  When used in a diversion, this will embed in  the  diversion  an
                  object  which,  when reread, will cause the contents of filename
                  to be transparently copied  through  to  the  output.   In  UNIX
                  troff, the contents of filename is immediately copied through to
                  the output regardless of whether there is a  current  diversion;
                  this behaviour is so anomalous that it must be considered a bug.
           .ev xx If xx is not a number, this will switch to a  named  environment
                  called  xx.  The environment should be popped with a matching ev
                  request without any arguments, just  as  for  numbered  environ-
                  ments.   There  is no limit on the number of named environments;
                  they will be created the first time that they are referenced.
           .ss m n
                  When two arguments are given to the ss request, the second argu-
                  ment  gives  the sentence space size.  If the second argument is
                  not given, the sentence space size will be the same as the  word
                  space  size.  Like the word space size, the sentence space is in
                  units of one twelfth of the spacewidth parameter for the current
                  font.  Initially both the word space size and the sentence space
                  size are 12.  Contrary to UNIX troff,  GNU  troff  handles  this
                  request  in  nroff mode also; a given value is then rounded down
                  to the nearest multiple of 12.  The sentence space size is  used
                  in  two  circumstances.   If the end of a sentence occurs at the
                  end of a line in fill mode, then both an inter-word space and  a
                  sentence  space will be added; if two spaces follow the end of a
                  sentence in the middle of a line, then the second space will  be
                  a sentence space.  Note that the behaviour of UNIX troff will be
                  exactly that exhibited by GNU troff  if  a  second  argument  is
                  never  given to the ss request.  In GNU troff, as in UNIX troff,
                  you should always follow a sentence with either a newline or two
           .ta n1 n2...nn T r1 r2...rn
                  Set tabs at positions n1, n2,..., nn and then set tabs at nn+r1,
                  nn+r2,..., nn+rn and then at nn+rn+r1,  nn+rn+r2,...,  nn+rn+rn,
                  and so on.  For example,
                         .ta T .5i
                  will set tabs every half an inch.
       New number registers
           The following read-only registers are available:
                  1 if colors are enabled, 0 otherwise.
                  The skew of the last character added to the current environment.
                  The skew of a character is how far to the right of the center of
                  a character the center of an accent over that  character  should
                  be placed.
                  The  name  or  number  of  the  current  environment.  This is a
                  string-valued register.
                  The current font family.  This is a string-valued register.
                  The current (internal) real font name.  This is a  string-valued
                  register.   If the current font is a style, the value of \n[.fn]
                  is the proper concatenation of family and style name.
                  The number of the next free font position.
           \n[.g] Always 1.  Macros should use this to determine whether they  are
                  running under GNU troff.
                  The current hyphenation language as set by the hla request.
                  The  number  of  immediately  preceding  consecutive  hyphenated
                  The maximum allowed number of consecutive hyphenated  lines,  as
                  set by the hlm request.
                  The current hyphenation flags (as set by the hy request).
                  The current hyphenation margin (as set by the hym request).
                  The current hyphenation space (as set by the hys request).
                  The indent that applies to the current output line.
                  The line length that applies to the current output line.
                  The title length as set by the lt request.
                  The amount of space that was needed in the last ne request  that
                  caused  a  trap  to  be  sprung.  Useful in conjunction with the
                  \n[.trunc] register.
                  1 if no-space mode is active, 0 otherwise.
                  The number of the next page,  either  the  value  set  by  a  pn
                  request, or the number of the current page plus 1.
                  The current pointsize in scaled points.
                  The last-requested pointsize in scaled points.
                  The  current  post-vertical  line  space  as  set  with  the pvs
                  The number of lines to be  right-justified  as  set  by  the  rj
                  The  last  requested  pointsize in points as a decimal fraction.
                  This is a string-valued register.
                  These give the values of the parameters set  by  the  first  and
                  second arguments of the ss request.
                  A string representation of the current tab settings suitable for
                  use as an argument to the ta request.
                  The amount of vertical space  truncated  by  the  most  recently
                  sprung  vertical  position trap, or, if the trap was sprung by a
                  ne request, minus the amount of vertical motion produced by  the
                  ne request.  In  other  words, at the point  a  trap is  sprung,
                  it represents the difference  of   what  the  vertical  position
                  would have been but for the trap, and what the vertical position
                  actually is.  Useful in conjunction with the \n[.ne] register.
           \n[.Y] The revision number of groff.
                  These four registers are set by the .psbb  request  and  contain
                  the  bounding  box  values  (in  PostScript  units)  of  a given
                  PostScript image.
           The following read/write registers are set by the \w escape sequence:
                  Like the st and sb registers, but take account  of  the  heights
                  and depths of characters.
                  The  amount  of horizontal space (possibly negative) that should
                  be added to the last character before a subscript.
                  How far to right of the center of the last character in  the  \w
                  argument,  the  center  of an accent from a roman font should be
                  placed over that character.
           Other available read/write number registers are:
           \n[c.] The current input line number.  \n[.c] is a read-only  alias  to
                  this register.
                  The number of hours past midnight.  Initialized at start-up.
           \n[hp] The current horizontal position at input line.
                  The  number of minutes after the hour.  Initialized at start-up.
                  The number of seconds after the minute.  Initialized  at  start-
                  The  return  value of the system() function executed by the last
                  sy request.
                  If greater than 0, the maximum number of objects  on  the  input
                  stack.   If  less  than  or equal to 0, there is no limit on the
                  number of objects on the input stack.  With no limit,  recursion
           Fonts not listed in the DESC file are automatically mounted on the next
           available font position when they are referenced.  If a font is  to  be
           mounted  explicitly  with the fp request on an unused font position, it
           should be mounted on the first unused font position, which can be found
           in the \n[.fp] register; although troff does not enforce this strictly,
           it will not allow a font to be mounted at a position  whose  number  is
           much greater than that of any currently used position.
           Interpolating a string does not hide existing macro arguments.  Thus in
           a macro, a more efficient way of doing
                  .xx \\$@
           If the font description file  contains  pairwise  kerning  information,
           characters  from  that  font  will  be  kerned.   Kerning  between  two
           characters can be inhibited by placing a \& between them.
           In a string comparison in a condition, characters that appear  at  dif-
           ferent input levels to the first delimiter character will not be recog-
           nised as the second or third delimiters.  This applies also to  the  tl
           request.   In  a \w escape sequence, a character that appears at a dif-
           ferent input level to the starting  delimiter  character  will  not  be
           recognised  as  the  closing delimiter character.  The same is true for
           \A, \b, \B, \C, \l, \L, \o, \X, and  \Z.   When  decoding  a  macro  or
           string  argument  that  is delimited by double quotes, a character that
           appears at a different input level to the starting delimiter  character
           will  not be recognised as the closing delimiter character.  The imple-
           mentation of \$@ ensures that the double quotes surrounding an argument
           will  appear the same input level, which will be different to the input
           level of the argument itself.  In a long escape name ] will not be rec-
           ognized  as a closing delimiter except when it occurs at the same input
           level as the opening ].  In compatibility mode, no attention is paid to
           the input-level.
           There are some new types of condition:
           .if rxxx
                  True if there is a number register named xxx.
           .if dxxx
                  True  if  there  is a string, macro, diversion, or request named
           .if mxxx
                  True if there is a color named xxx.
           .if cch
                  True if there is a character ch available; ch is either an ASCII
                  . nop Done.


           This section describes the format output by GNU troff.  The output for-
           mat used by GNU troff is very similar to that used by Unix device-inde-
           pendent troff.  Only the differences are documented here.
           The  argument  to the s command is in scaled points (units of points/n,
           where n is the argument to the sizescale command  in  the  DESC  file).
           The argument to the x Height command is also in scaled points.
       Text Commands
           Nn     Print  character  with  index  n (a non-negative integer) of the
                  current font.
           If the tcommand line is present in the DESC file, troff  will  use  the
           following two commands.
           txxx   xxx  is  any  sequence  of characters terminated by a space or a
                  newline; the first character should be printed  at  the  current
                  position, the current horizontal position should be increased by
                  the width of the first character, and so on for each  character.
                  The  width  of  the  character  is  that given in the font file,
                  appropriately scaled for the current point size, and rounded  so
                  that  it  is  a  multiple of the horizontal resolution.  Special
                  characters cannot be printed using this command.
           un xxx This is 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 n.
           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; drivers
           should not assume that they will be only two characters long.
           When a character is to be printed, that character will always be in the
           current font.  Unlike device-independent troff, it is not necessary for
           drivers to search special fonts to find a character.
           For color support, some new commands have been added:
           mc cyan magenta yellow
           mg gray
           mk cyan magenta yellow black
           mr red green blue
           Df n\n Set the shade of gray to be used for filling solid objects to n;
                  n  must  be  an  integer between 0 and 1000, where 0 corresponds
                  solid white and 1000 to solid black, and values in between  cor-
                  respond  to  intermediate  shades of gray.  This applies only to
                  solid circles, solid ellipses and solid polygons.  By default, a
                  level  of 1000 will be used.  Whatever color a solid object has,
                  it should completely obscure everything  beneath  it.   A  value
                  greater  than  1000  or less than 0 can also be used: this means
                  fill with the shade of gray that is  currently  being  used  for
                  lines  and  text.  Normally this will be black, but some drivers
                  may provide a way of changing this.
           DC d\n Draw a solid circle with a diameter of d with the leftmost point
                  at the current position.
           DE dx dy\n
                  Draw a solid ellipse with a horizontal diameter of dx and a ver-
                  tical diameter of dy with the  leftmost  point  at  the  current
           Dp dx1 dy1 dx2 dy2 ... dxn dyn\n
                  Draw  a  polygon  with,  for i=1,...,n+1, the i-th vertex at the
                  current position +i<I>j?1(dxj,dyj).  At the  moment,  GNU  pic  only
                  uses this command to generate triangles and rectangles.
           DP dx1 dy1 dx2 dy2 ... dxn dyn\n
                  Like Dp but draw a solid rather than outlined polygon.
           Dt n\n Set  the  current line thickness to n machine units.  Tradition-
                  ally Unix troff drivers use a line thickness proportional to the
                  current  point size; drivers should continue to do this if no Dt
                  command has been given, or if a Dt command has been given with a
                  negative  value  of  n.   A zero value of n selects the smallest
                  available line thickness.
           A difficulty arises in how the current position should be changed after
           the execution of these commands.  This is not of great importance since
           the code generated by GNU pic does not depend on this.  Given a drawing
           command of the form
                  \D?c x1 y1 x2 y2 ... xn yn?
           where  c  is not one of c, e, l, a, or ~, Unix troff will treat each of
           the xi as a horizontal quantity, and each of the yi as a vertical quan-
           tity  and  will assume that the width of the drawn object is in?1xi, and
           that the height is in?1yi.  (The assumption about the height can be seen
           by  examining the st and sb registers after using such a D command in a
           \w escape sequence).  This rule also holds for all the original drawing
           commands  with  the exception of De.  For the sake of compatibility GNU
           troff also follows this rule, even though it produces an ugly result in
           the  case  of the Dt, and, to a lesser extent, DE commands.  Thus after
                  commands above.
           Note  that  Df  is  now  mapped  onto  DFg.  The current position isn't
           changed by those colour commands.
       Device Control Commands
           There is a continuation convention which permits the  argument  to  the
           x X  command  to  contain newlines: when outputting the argument to the
           x X command, GNU troff will follow each newline in the argument with  a
           +  character  (as  usual,  it will terminate the entire argument with a
           newline); thus if the line after the line containing  the  x X  command
           starts with +, then the newline ending the line containing the x X com-
           mand should be treated as part of the argument to the x X command,  the
           + should be ignored, and the part of the line following the + should be
           treated like the part of the line following the x X command.
           The first three output commands are guaranteed to be:
                  x T device
                  x res n h v
                  x init


           In spite of the many extensions, groff has  retained  compatibility  to
           classical  troff to a large degree.  For the cases where the extensions
           lead to collisions, a special compatibility mode with  the  restricted,
           old functionality was created for groff.
       Groff Language
           groff  provides  a  compatibility mode that allows to process roff code
           written for classical or for other implementations of roff in a consis-
           tent way.
           Compatibility  mode  can  be turned on with the -C command line option,
           and turned on or off with the .cp request.  The number  register  \n(.C
           is 1 if compatibility mode is on, 0 otherwise.
           This  became  necessary  because  the GNU concept for long names causes
           some incompatibilities.  Classical troff interprets
           as defining a string ab with contents cd.  In groff mode, this will  be
           considered as a call of a macro named dsabcd.
           Also classical troff interprets \*[ or \n[ as references to a string or
           number register called [ while groff takes this as the start of a  long
           In compatibility mode, groff interprets these things in the traditional
           way; so long names are not recognized.
                  .ps 10u
           will set the pointsize to 10 points, whereas in groff native  mode  the
           pointsize will be set to 10 scaled points.
           In  groff  mode,  there is a fundamental difference between unformatted
           input characters, and formatted  output  characters.   Everything  that
           affects how an output character will be output is stored with the char-
           acter; once an output character has been constructed it  is  unaffected
           by  any  subsequent  requests  that are executed, including the bd, cs,
           tkf, tr, or fp requests.
           Normally output characters are constructed from input characters at the
           moment  immediately before the character is added to the current output
           line.  Macros, diversions and strings are all, in fact, the  same  type
           of object; they contain lists of input characters and output characters
           in any combination.
           An output character does not behave like an  input  character  for  the
           purposes  of  macro  processing; it does not inherit any of the special
           properties that the input character from which it was constructed might
           have had.  The following example will make things clearer.
                  .di x
           In  GNU  mode  this will be printed as \\.  So each pair of input back-
           slashes '\\' is turned into a  single  output  backslash  '\'  and  the
           resulting  output  backslashes are not interpreted as escape characters
           when they are reread.
           Classical troff would interpret them as  escape  characters  when  they
           were reread and would end up printing a single backslash '\'.
           In  GNU,  the  correct  way to get a printable version of the backslash
           character '\' is the \(rs escape sequence, but classical troff does not
           provide  a  clean  feature  for getting a non-syntactical backslash.  A
           close method is the printable version of the current  escape  character
           using  the \e escape sequence; this works if the current escape charac-
           ter is not redefined.  It works in  both  GNU  mode  and  compatibility
           mode,  while  dirty tricks like specifying a sequence of multiple back-
           slashes do not work reliably; for the different handling in diversions,
           macro  definitions, or text mode quickly leads to a confusion about the
           necessary number of backslashes.
           To store an escape sequence in a diversion  that  will  be  interpreted
           when  the  diversion  is  reread, either the traditional \! transparent
           output facility or the new \? escape sequence can be used.
           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 on your system, it is also available on-line at the GNU
           copyleft site  <>.   This  document
           was  written  by  James  Clark,  with  modifications  by Werner Lemberg
           <> and Bernd Warken <>.
           This document is part of groff, the GNU roff  distribution.   Formerly,
           the  contents  of  this  document was kept in the manual page troff(1).
           Only the parts dealing with the language aspects of the different  roff
           systems  were  carried over into this document.  The troff command line
           options and warnings are still documented in troff(1).


           The groff info file,  cf.  info(1)  presents  all  groff  documentation
           within a single document.
                  A list of all documentation around groff.
                  A description of the groff language, including a short, but com-
                  plete reference  of  all  predefined  requests,  registers,  and
                  escapes  of  plain groff.  From the command line, this is called
                  shell# man 7 groff
                  A survey of roff systems, including pointers to further histori-
                  cal documentation.
           [CSTR #54]
                  The  Nroff/Troff  User's  Manual  by J. F. Osanna of 1976 in the
                  revision of Brian Kernighan of 1992, being the  classical  troff
                  documentation <>.

    Groff Version 05 July 2002 GROFF_DIFF(7)


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