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GROFF(7)							      GROFF(7)

NAME
       groff - a short reference for the GNU roff language

DESCRIPTION
       The  name  groff	 stands for GNU roff and is the free implementation of
       the roff type-setting system.  See roff(7) for a survey and  the	 back‐
       ground of the groff system.

       This document gives only short descriptions of the predefined roff lan‐
       guage elements as used in groff.	 Both the classical features  and  the
       groff extensions are provided.

       Historically,  the roff language was called troff.  groff is compatible
       with the classical system and provides proper extensions.  So  in  GNU,
       the  terms  roff,  troff, and groff language could be used as synonyms.
       However troff slightly tends to refer more to  the  classical  aspects,
       whereas	groff  emphasizes  the GNU extensions, and roff is the general
       term for the language.

       This file is only a short version of the complete documentation that is
       found  in the groff info(1) file, which contains more detailed, actual,
       and concise information.

       The general syntax for writing groff documents is relatively easy,  but
       writing extensions to the roff language can be a bit harder.

       The roff language is line-oriented.  There are only two kinds of lines,
       control lines and text lines.  The control lines start with  a  control
       character,  by  default	a period “.”  or a single quote “'”; all other
       lines are text lines.

       Control lines represent commands, optionally with arguments.  They have
       the following syntax.  The leading control character can be followed by
       a command name; arguments, if any, are separated	 by  blanks  from  the
       command name and among themselves, for example,

	      .command_name arg1 arg2

       For  indentation, any number of space or tab characters can be inserted
       between the leading control character and the  command  name,  but  the
       control character must be on the first position of the line.

       Text lines represent the parts that will be printed.  They can be modi‐
       fied by escape sequences, which are recognized by a  leading  backslash
       ‘\’.   These  are  in-line or even in-word formatting elements or func‐
       tions.  Some of these take arguments separated by  single  quotes  “'”,
       others  are regulated by a length encoding introduced by an open paren‐
       thesis ‘(’ or enclosed in brackets ‘[’ and ‘]’.

       The roff language provides flexible instruments	for  writing  language
       extension,  such	 as  macros.  When interpreting macro definitions, the
       roff system enters a special operating mode, called the copy mode.

       The copy mode behavior can be quite tricky, but there  are  some	 rules
       that ensure a safe usage.

       1.     Printable	 backslashes  must  be denoted as \e.  To be more pre‐
	      cise, \e represents the current  escape  character.   To	get  a
	      backslash glyph, use \(rs or \[rs].

       2.     Double all backslashes.

       3.     Begin all text lines with the special non-spacing character \&.

       This  does not produce the most efficient code, but it should work as a
       first measure.  For better strategies, see  the	groff  info  file  and
       groff_tmac(5).

       Reading roff source files is easier, just reduce all double backslashes
       to a single one in all macro definitions.

GROFF ELEMENTS
       The roff language elements add formatting information to a  text	 file.
       The  fundamental	 elements  are	predefined commands and variables that
       make roff a full-blown programming language.

       There  are  two	kinds  of  roff	 commands,  possibly  with  arguments.
       Requests	 are written on a line of their own starting with a dot ‘.’ or
       a “'”, whereas Escape sequences are in-line functions and in-word  for‐
       matting elements starting with a backslash ‘\’.

       The  user  can define her own formatting commands using the de request.
       These commands are called  macros,  but	they  are  used	 exactly  like
       requests.  Macro packages are pre-defined sets of macros written in the
       groff language.	A user's possibilities to create escape sequences her‐
       self is very limited, only special characters can be mapped.

       The  groff  language provides several kinds of variables with different
       interfaces.  There are pre-defined variables, but the user  can	define
       her own variables as well.

       String  variables  store character sequences.  They are set with the ds
       request and retrieved by the \* escape  sequences.   Strings  can  have
       variables.

       Register	 variables  can	 store	numerical values, numbers with a scale
       unit, and occasionally string-like objects.  They are set with  the  nr
       request and retrieved by the \n escape sequences.

       Environments  allow  the	 user  to  temporarily store global formatting
       parameters like line length, font size, etc. for later reuse.  This  is
       done by the ev request.

       Fonts  are  identified  either by a name or by an internal number.  The
       current font is chosen by the ft request or by the \f escape sequences.
       Each  device  has  special fonts, but the following fonts are available
       for all devices.	 R is the standard font Roman.	B is its bold counter‐
       part.   The italic font is called I and is available everywhere, but on
       text devices it is displayed as an  underlined  Roman  font.   For  the
       graphical  output devices, there exist constant-width pendants of these
       fonts, CR, CI, and CB.  On text devices, all characters have a constant
       width anyway.

       Moreover,  there	 are  some advanced roff elements.  A diversion stores
       information into a macro for later usage.  A trap is a positional  con‐
       dition  like  a certain number of lines from page top or in a diversion
       or in the input.	 Some action can be prescribed to be run automatically
       when the condition is met.

       More  detailed  information and examples can be found in the groff info
       file.

CONTROL CHARACTERS
       There is a small set of characters that have a special controlling task
       in certain conditions.

       .      A	 dot  is  only special at the beginning of a line or after the
	      condition in the requests if, ie, el, and while.	 There	it  is
	      the control character that introduces a request (or macro).  The
	      special behavior can be delayed by using	the  \.	  escape.   By
	      using the cc request, the control character can be set to a dif‐
	      ferent character, making the dot ‘.’ a non-special character.

	      In all other positions, it just means a dot character.  In  text
	      paragraphs,  it is advantageous to start each sentence at a line
	      of its own.

       '      The single quote has two controlling tasks.  At the beginning of
	      a	 line  and  in the conditional requests it is the non-breaking
	      control character.  That means that it introduces a request like
	      the  dot,	 but  with  the	 additional property that this request
	      doesn't cause a linebreak.  By using the c2  request,  the  non-
	      break control character can be set to a different character.

	      As  a second task, it is the most commonly used argument separa‐
	      tor in some functional escape sequences (but any pair of charac‐
	      ters  not	 part  of the argument will work).  In all other posi‐
	      tions, it denotes the  single  quote  or	apostrophe  character.
	      Groff  provides  a printable representation with the \(cq escape
	      sequence.

       "      The double quote is  used	 to  enclose  arguments	 in  requests,
	      macros,  and strings.  In the ds and as requests, a leading dou‐
	      ble quote in the argument will be stripped  off,	making	every‐
	      thing else afterwards the string to be defined (enabling leading
	      whitespace).  The escaped double quote \" introduces a  comment.
	      Otherwise, it is not special.  Groff provides a printable repre‐
	      sentation with the \(dq escape sequence.

       \      The backslash usually introduces an escape sequence (this can be
	      changed  with  the ec request).  A printed version of the escape
	      character is the \e escape; a backslash glyph can be obtained by
	      \(rs.

       (      The  open	 parenthesis  is only special in escape sequences when
	      introducing an escape name or argument consisting of exactly two
	      characters.   In	groff, this behavior can be replaced by the []
	      construct.

       [      The opening bracket is only special in groff  escape  sequences;
	      there  it is used to introduce a long escape name or long escape
	      argument.	 Otherwise, it is non-special, e.g. in macro calls.

       ]      The closing bracket is only special in groff  escape  sequences;
	      there  it terminates a long escape name or long escape argument.
	      Otherwise, it is non-special.

       space  Space characters are only functional characters.	They  separate
	      the arguments in requests, macros, and strings, and the words in
	      text lines.  They are subject to groff's horizontal spacing cal‐
	      culations.   To get a defined space width, escape sequences like
	      ‘\ ’ (this is the escape character followed by a space), \|, \^,
	      or \h should be used.

       newline
	      In  text	paragraphs,  newlines mostly behave like space charac‐
	      ters.  Continuation lines can be specified by  an	 escaped  new‐
	      line,  i.e., by specifying a backslash ‘\’ as the last character
	      of a line.

       tab    If a tab character occurs during text the	 interpreter  makes  a
	      horizontal  jump to the next pre-defined tab position.  There is
	      a sophisticated interface for handling tab positions.

NUMERICAL EXPRESSIONS
       A numerical value is a signed or unsigned  integer  or  float  with  or
       without	an  appended scaling indicator.	 A scaling indicator is a one-
       character abbreviation for a unit of measurement.  A number followed by
       a scaling indicator signifies a size value.  By default, numerical val‐
       ues do not have a scaling indicator, i.e., they are normal numbers.

       The roff language defines the following scaling indicators.

	      c		Centimeter
	      i		Inch
	      P		Pica = 1/6 inch
	      p		Point = 1/72 inch
	      m		Em = the font size in points (width of letter `m')
	      M		100th of an Em
	      n		En = Em/2
	      u		Basic unit for actual output device
	      v		Vertical   line	  space	  in   basic   units	scaled
			point = 1/sizescale  of	 a point (defined in font DESC
			file)
	      f		Scale by 65536.

       Numerical expressions are combinations of the numerical values  defined
       above  with  the	 following  arithmetical  operators already defined in
       classical troff.

	      +		Addition
	      -		Subtraction
	      *		Multiplication
	      /		Division
	      %		Modulo
	      =		Equals
	      ==	Equals
	      <		Less than
	      >		Greater than
	      <=	Less or equal
	      >=	Greater or equal
	      &		Logical and
	      :		Logical or
	      !		Logical not
	      (		Grouping of expressions
	      )		Close current grouping

       Moreover, groff added the following  operators  for  numerical  expres‐
       sions:

	      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.

       For details see the groff info file.

CONDITIONS
       Conditions occur in tests raised by the if, ie, and the while requests.
       The following table characterizes the different types of conditions.

	      N		A numerical expression N yields true if its  value  is
			greater than 0.
	      !N	True if the value of I is 0.
	      's1's2'	True if string s1 is identical to string s2.
	      !'s1's2'	True if string s1 is not identical to string s2.
	      cch	True if there is a character ch available.
	      dname	True  if  there	 is  a	string,	 macro,	 diversion, or
			request called name.
	      e		Current page number is even.
	      o		Current page number is odd.
	      mname	True if there is a color called name.
	      n		Formatter is nroff.
	      rreg	True if there is a register named reg.
	      t		Formatter is troff.

REQUESTS
       This section provides a short reference for  the	 predefined  requests.
       In groff, request and macro names can be arbitrarily long.  No bracket‐
       ing or marking of long names is needed.

       Most requests take one or more arguments.  The arguments are  separated
       by  space  characters  (no tabs!); there is no inherent limit for their
       length or number.  An argument can be enclosed  by  a  pair  of	double
       quotes.	 This  is very handy if an argument contains space characters,
       e.g., "arg with space" denotes a single argument.

       Some requests have optional arguments with a different behaviour.   Not
       all  of	these details are outlined here.  Refer to the groff info file
       and groff_diff(7) for all details.

       In the following request specifications, most argument names were  cho‐
       sen  to be descriptive.	Only the following denotations need clarifica‐
       tion.

	      c		denotes a single character.
	      font	a font either specified as a font name or a font  num‐
			ber.
	      anything	all  characters up to the end of the line or within \{
			and \}.
	      n		is a numerical expression that evaluates to an integer
			value.
	      N		is   an	 arbitrary  numerical  expression,  signed  or
			unsigned.
	      ±N	has three meanings depending on	 its  sign,  described
			below.

       If  an  expression  defined  as ±N starts with a ‘+’ sign the resulting
       value of the expression will be added  to  an  already  existing	 value
       inherent	 to the related request, e.g. adding to a number register.  If
       the expression starts with a ‘-’ the value of the  expression  will  be
       subtracted from the request value.

       Without	a  sign,  N replaces the existing value directly.  To assign a
       negative number either prepend 0 or  enclose  the  negative  number  in
       parentheses.

   Request Short Reference
       .	 Empty line, ignored.  Useful for structuring documents.
       .\" anything
		 Complete line is a comment.
       .ab string
		 Print string on standard error, exit program.
       .ad	 Begin	line  adjustment  for  output  lines in current adjust
		 mode.
       .ad c	 Start line adjustment in mode c (c=l,r,b,n).
       .af register c
		 Assign format c to register (c=l,i,I,a,A).
       .aln alias register
		 Create alias name for register.
       .als alias object
		 Create alias name for request, string,	 macro,	 or  diversion
		 object.
       .am macro Append to macro until .. is encountered.
       .am macro end
		 Append to macro until .end is called.
       .ami macro
		 Append	 to a macro whose name is contained in the string reg‐
		 ister macro until .. is encountered.
       .ami macro end
		 Append to a macro indirectly.	macro and end are string  reg‐
		 isters whose contents are interpolated for the macro name and
		 the end macro, respectively.
       .am1 macro
		 Same as .am but with compatibility mode switched  off	during
		 macro expansion.
       .am1 macro end
		 Same  as  .am but with compatibility mode switched off during
		 macro expansion.
       .as stringvar anything
		 Append anything to stringvar.
       .asciify diversion
		 Unformat ASCII characters, spaces, and some escape  sequences
		 in diversion.
       .as1 stringvar anything
		 Same  as  .as but with compatibility mode switched off during
		 string expansion.
       .backtrace
		 Print a backtrace of the input on stderr.
       .bd font N
		 Embolden font by N-1 units.
       .bd S font N
		 Embolden Special Font S when current font is font.
       .blm	 Unset the blank line macro.
       .blm macro
		 Set the blank line macro to macro.
       .box	 End current diversion.
       .box macro
		 Divert to macro, omitting a partially filled line.
       .boxa	 End current diversion.
       .boxa macro
		 Divert and append to macro, omitting a partially filled line.
       .bp	 Eject current page and begin new page.
       .bp ±N	 Eject current page; next page number ±N.
       .br	 Line break.
       .brp	 Break and spread output line.	Same as \p.
       .break	 Break out of a while loop.
       .c2	 Reset no-break control character to “'”.
       .c2 c	 Set no-break control character to c.
       .cc	 Reset control character to ‘.’.
       .cc c	 Set control character to c.
       .ce	 Center the next input line.
       .ce N	 Center following N input lines.
       .cf filename
		 Copy contents of file filename unprocessed to	stdout	or  to
		 the diversion.
       .cflags mode c1 c2 ...
		 Treat characters c1, c2, ... according to mode number.
       .ch trap N
		 Change trap location to N .
       .char c anything
		 Define character c as string anything.
       .chop object
		 Chop  the  last  character  off  macro,  string, or diversion
		 object.
       .close stream
		 Close the stream.
       .color	 Enable colors.
       .color N	 If N is zero disable colors, otherwise enable them.
       .continue Finish the current iteration of a while loop.
       .cp	 Enable compatibility mode.
       .cp N	 If N is zero disable compatibility mode, otherwise enable it.
       .cs font N M
		 Set constant character width mode for font to N/36  ems  with
		 em M.
       .cu N	 Continuous underline in nroff, like .ul in troff.
       .da	 End current diversion.
       .da macro Divert and append to macro.
       .de macro Define or redefine macro until .. is encountered.
       .de macro end
		 Define or redefine macro until .end is called.
       .de1 macro
		 Same  as  .de but with compatibility mode switched off during
		 macro expansion.
       .de1 macro end
		 Same as .de but with compatibility mode switched  off	during
		 macro expansion.
       .defcolor color scheme component
		 Define	 or  redefine  a color with name color.	 scheme can be
		 rgb, cym, cymk, gray, or grey.	 component can be single  com‐
		 ponents  specified  as fractions in the range 0 to 1 (default
		 scaling indicator f), as a string  of	two-digit  hexadecimal
		 color	components  with  a leading #, or as a string of four-
		 digit hexadecimal components with two leading #.   The	 color
		 default can't be redefined.
       .dei macro
		 Define	 or  redefine  a  macro whose name is contained in the
		 string register macro until .. is encountered.
       .dei macro end
		 Define or redefine a macro indirectly.	  macro	 and  end  are
		 string	 registers  whose  contents  are  interpolated for the
		 macro name and the end macro, respectively.
       .di	 End current diversion.
       .di macro Divert to macro .
       .do name	 Interpret .name with compatibility mode disabled.
       .ds stringvar anything
		 Set stringvar to anything.
       .ds1 stringvar anything
		 Same as .ds but with compatibility mode switched  off	during
		 string expansion.
       .dt N trap
		 Set  diversion	 trap  to  position N (default scaling indica‐
		 tor v).
       .ec	 Reset escape character to ‘\’.
       .ec c	 Set escape character to c.
       .ecr	 Restore escape character saved with .ecs.
       .ecs	 Save current escape character.
       .el anything
		 Else part for if-else (ie) request.
       .em macro The macro will be run after the end of input.
       .eo	 Turn off escape character mechanism.
       .ev	 Switch to previous environment.
       .ev env	 Push down environment number or name env and switch to it.
       .evc env	 Copy the contents of environment env to the current  environ‐
		 ment.	No pushing or popping.
       .ex	 Exit from roff processing.
       .fam	 Return to previous font family.
       .fam name Set the current font family to name.
       .fc	 Disable field mechanism.
       .fc a	 Set field delimiter to a and pad character to space.
       .fc a b	 Set field delimiter to a and pad character to b.
       .fchar c anything
		 Define fallback character c as string anything.
       .fi	 Fill output lines.
       .fl	 Flush output buffer.
       .fp n font
		 Mount font on position n.
       .fp n internal external
		 Mount	font with long external name to short internal name on
		 position n.
       .fspecial font s1 s2 ...
		 When the current font is font, then the  fonts	 s1,  s2,  ...
		 will be special.
       .ft	 Return to previous font.  Same as \f[] or \fP.
       .ft font	 Change	 to  font name or number font; same as \f[font] escape
		 sequence.
       .ftr font1 font2
		 Translate font1 to font2.
       .hc	 Remove additional hyphenation indicator character.
       .hc c	 Set up additional hyphenation indicator character c.
       .hcode c1 code1 c2 code2 ...
		 Set the hyphenation code of character c1 to code1, that of c2
		 to code2, etc.
       .hla lang Set the current hyphenation language to lang.
       .hlm n	 Set the maximum number of consecutive hyphenated lines to n.
       .hpf file Read hyphenation patterns from file.
       .hpfa file
		 Append hyphenation patterns from file.
       .hpfcode file
		 Set input mapping for .hpf.
       .hw words List of words with exceptional hyphenation.
       .hy N	 Switch to hyphenation mode N.
       .hym n	 Set  the  hyphenation	margin	to  n (default scaling indica‐
		 tor m).
       .hys n	 Set the hyphenation space to n.
       .ie cond anything
		 If cond then anything else goto .el.
       .if cond anything
		 If cond then anything; otherwise do nothing.
       .ig	 Ignore text until .. is encountered.
       .ig end	 Ignore text until .end.
       .in	 Change to previous indent value.
       .in ±N	 Change indent according to ±N (default scaling indicator m).
       .it N trap
		 Set an input-line count trap for the next N lines.
       .itc N trap
		 Same as .it but count lines interrupted with \c as one line.
       .kern	 Enable pairwise kerning.
       .kern n	 If n is zero, disable pairwise kerning, otherwise enable it.
       .lc	 Remove leader repetition character.
       .lc c	 Set leader repetition character to c.
       .length register anything
		 Write the length of the string anything in register.
       .linetabs Enable line-tabs mode (i.e., calculate tab positions relative
		 to output line).
       .linetabs n
		 If n is zero, disable line-tabs mode, otherwise enable it.
       .lf N file
		 Set input line number to N and filename to file.
       .lg N	 Ligature mode on if N>0.
       .ll	 Change to previous line length.
       .ll ±N	 Set  line  length according to ±N (default size 6.5i, default
		 scaling indicator m).
       .ls	 Change to the previous value of additional intra-line skip.
       .ls N	 Set additional intra-line skip value to N,  i.e.,  N-1	 blank
		 lines are inserted after each text output line.
       .lt ±N	 Length of title (default scaling indicator m).
       .mc	 Margin character off.
       .mc c	 Print	character  c  after  each text line at actual distance
		 from right margin.
       .mc c N	 Set margin character to c and distance to N from right margin
		 (default scaling indicator m).
       .mk register
		 Mark current vertical position in register.
       .mso file The  same  as the .so request except that file is searched in
		 the tmac directories.
       .na	 No output-line adjusting.
       .ne	 Need a one-line vertical space.
       .ne N	 Need N vertical space (default scaling indicator v).
       .nf	 No filling or adjusting of output-lines.
       .nh	 No hyphenation.
       .nm	 Number mode off.
       .nm ±N [M [S [I]]]
		 In line number	 mode,	set  number,  multiple,	 spacing,  and
		 indent.
       .nn	 Do not number next line.
       .nn N	 Do not number next N lines.
       .nop anything
		 Always execute anything.
       .nr register ±N M
		 Define or modify register using ±N with auto-increment M.
       .nroff	 Make the built-in condition n true and t false.
       .ns	 Turn no-space mode on.
       .nx	 Immediately jump to end of current file.
       .nx filename
		 Next file.
       .open stream filename
		 Open  register	 filename for writing and associate the stream
		 named register stream with it.
       .opena stream filename
		 Like .open but append to it.
       .os	 Output vertical distance that was saved by the sv request.
       .output string
		 Emit string directly to intermediate output, allowing leading
		 whitespace  if	 string	 starts with " (which will be stripped
		 off).
       .pc	 Reset page number character to ‘%’.
       .pc c	 Page number character.
       .pi program
		 Pipe output to program (nroff only).
       .pl	 Set page length to default 11i.  The current page  length  is
		 stored in register .p.
       .pl ±N	 Change page length to ±N (default scaling indicator v).
       .pm	 Print macro names and sizes (number of blocks of 128 bytes).
       .pm t	 Print	only  total  of	 sizes	of macros (number of 128 bytes
		 blocks).
       .pn ±N	 Next page number N.
       .pnr	 Print the names and contents of all currently defined	number
		 registers on stderr.
       .po	 Change	 to  previous page offset.  The current page offset is
		 available in register .o.
       .po ±N	 Page offset N.
       .ps	 Return to previous point-size.
       .ps ±N	 Point size; same as \s[±N].
       .psbb filename
		 Get the bounding box of a PostScript image filename.
       .pso command
		 This behaves like the so request except that input comes from
		 the standard output of command.
       .ptr	 Print	the  names  and	 positions of all traps (not including
		 input line traps and diversion traps) on stderr.
       .pvs	 Change to previous post-vertical line spacing.
       .pvs ±N	 Change post-vertical line spacing according  to  ±N  (default
		 scaling indicator p).
       .rchar c1 c2 ...
		 Remove the definitions of characters c1, c2, ...
       .rd prompt
		 Read insertion.
       .return	 Return from a macro.
       .rj n	 Right justify the next n input lines.
       .rm name	 Remove request, macro, or string name.
       .rn old new
		 Rename request, macro, or string old to new.
       .rnn reg1 reg2
		 Rename register reg1 to reg2.
       .rr register
		 Remove register.
       .rs	 Restore spacing; turn no-space mode off.
       .rt ±N	 Return	 (upward only) to marked vertical place (default scal‐
		 ing indicator v).
       .shc	 Reset soft hyphen character to \(hy.
       .shc c	 Set the soft hyphen character to c.
       .shift n	 In a macro, shift the arguments by n positions.
       .sizes s1 s2 ... sn [0]
		 Set available font sizes similar to the sizes	command	 in  a
		 DESC file.
       .so filename
		 Include source file.
       .sp	 Skip one line vertically.
       .sp N	 Space	vertical  distance N up or down according to sign of N
		 (default scaling indicator v).
       .special s1 s2 ...
		 Fonts s1, s2, etc. are special and will be searched for char‐
		 acters not in the current font.
       .spreadwarn
		 Toggle	 the  spread  warning  on and off without changing its
		 value.
       .spreadwarn limit
		 Emit a warning if each space in an output line is widened  by
		 limit or more (default scaling indicator m).
       .ss N	 Space-character  size	set  to	 N/12 of the spacewidth in the
		 current font.
       .ss N M	 Space-character size set to N/12 and sentence space size  set
		 to M/12 of the spacewidth in the current font (=1/3 em).
       .sty n style
		 Associate style with font position n.
       .substring xx n1 n2
		 Replace the string named xx with the substring defined by the
		 indices n1 and n2.
       .sv	 Save 1v of vertical space.
       .sv N	 Save the  vertical  distance  N  for  later  output  with  os
		 request.
       .sy command-line
		 Execute program command-line.
       .ta T N	 Set  tabs  after  every  position  that  is  a	 multiple of N
		 (default scaling indicator m).
       .ta n1 n2 ... nn T r1 r2 ... rn
		 Set tabs at positions n1, n2,	...,  nn,  then	 set  tabs  at
		 nn+r1,	 nn+r2,	 ...,  nn+rn, then at nn+rn+r1, nn+rn+r2, ...,
		 nn+rn+rn, and so on.
       .tc	 Remove tab repition character.
       .tc c	 Set tab repetition character to c.
       .ti ±N	 Temporary indent next line (default scaling indicator m).
       .tkf font s1 n1 s2 n2
		 Enable track kerning for font.
       .tl ’left’center’right’
		 Three-part title.
       .tm anything
		 Print anything on terminal (UNIX standard message output).
       .tm1 anything
		 Print anything on terminal (UNIX  standard  message  output),
		 allowing  leading whitespace if anything starts with " (which
		 will be stripped off).
       .tmc anything
		 Similar to .tm1 without emitting a final newline.
       .tr abcd...
		 Translate a to b, c to d, etc. on output.
       .trf filename
		 Transparently output the contents of file filename.
       .trin abcd...
		 This is the same as the tr request except  that  the  asciify
		 request will use the character code (if any) before the char‐
		 acter translation.
       .trnt abcd...
		 This is the same as the tr request except that	 the  transla‐
		 tions	do  not apply to text that is transparently throughput
		 into a diversion with \!.
       .troff	 Make the built-in condition t true and n false.
       .uf font	 Underline font set to font (to be switched to by .ul).
       .ul N	 Underline (italicize in troff) N input lines.
       .unformat diversion
		 Unformat space characters and tabs, preserving font  informa‐
		 tion in diversion.
       .vpt n	 Enable vertical position traps if n is non-zero, disable them
		 otherwise.
       .vs	 Change to previous vertical base line spacing.
       .vs ±N	 Set vertical base line spacing according to ±N (default scal‐
		 ing indicator p).  Default value is 12p.
       .warn n	 Set warnings code to n.
       .warnscale si
		 Set scaling indicator used in warnings to si.
       .wh N	 Remove (first) trap at position N.
       .wh N trap
		 Set location trap; negative means from page bottom.
       .while cond anything
		 While condition cond is true, accept anything as input.
       .write stream anything
		 Write anything to the stream named stream.
       .writec stream anything
		 Similar to .write without emitting a final newline.
       .writem stream xx
		 Write	contents  of  macro  or	 string xx to the stream named
		 stream.

       Besides these standard groff requests, there  might  be	further	 macro
       calls.	They  can  originate  from a macro package (see roff(7) for an
       overview) or from a preprocessor.

       Preprocessor macros are easy to be recognized.  They enclose their code
       into a pair of characteristic macros.

		      ┌─────────────┬─────────────┬────────────┐
		      │preprocessor │ start macro │  end macro │
		      ├─────────────┼─────────────┼────────────┤
		      │	   eqn	    │	  .PS	  │    .PE     │
		      │	   grap	    │	  .G1	  │    .G2     │
		      │	   grn	    │	  .GS	  │    .GE     │
		      │	   pic	    │	  .PS	  │    .PE     │
		      │	  refer	    │	  .R1	  │    .R2     │
		      │	  soelim    │	 none	  │    none    │
		      │	   tbl	    │	  .TS	  │    .TE     │
		      └─────────────┴─────────────┴────────────┘
ESCAPE SEQUENCES
       Escape  sequences are in-line language elements usually introduced by a
       backslash ‘\’ and followed  by  an  escape  name	 and  sometimes	 by  a
       required	 argument.   Input  processing is continued directly after the
       escaped character or the argument resp. without an intervening  separa‐
       tion  character.	  So  there  must be a way to determine the end of the
       escape name and the end of the argument.

       This is done by enclosing names (escape name and	 arguments  consisting
       of a variable name) by a pair of brackets [name] and constant arguments
       (number expressions and characters) by apostrophes  (ASCII  0x27)  like
       ’constant’.

       There  are  abbreviations  for short names.  Two character escape names
       can be specified by an opening parenthesis like \(xy without a  closing
       counterpart.   And  all	one-character names different from the special
       characters ‘[’ and ‘(’ can even be specified without a  marker  in  the
       form \c.

       Constant	 arguments  of	length 1 can omit the marker apostrophes, too,
       but there is no two-character analogue.

       While 1-character escape sequences are mainly used  for	in-line	 func‐
       tions  and  system  related  tasks, the 2-letter names following the \(
       construct are used for special characters predefined by the  roff  sys‐
       tem.   Escapes sequences with names of more than two characters \[name]
       denote user defined named characters (see the char request).

   Single Character Escapes
       \"     Beginning of a comment.  Everything up to the end of the line is
	      ignored.
       \#     Everything  up  to  and  including  the next newline is ignored.
	      This is interpreted in copy mode.	 This is like \"  except  that
	      the terminating newline is ignored as well.
       \*s    The  string  stored in the string variable with 1-character name
	      s.
       \*(st  The string stored in the string variable with  2-character  name
	      st.
       \*[stringvar arg1 arg2 ...]
	      The  string  stored in the string variable with arbitrary length
	      name stringvar, taking arg1, arg2, ... as arguments.
       \$0    The name by which	 the  current  macro  was  invoked.   The  als
	      request can make a macro have more than one name.
       \$x    Macro  or	 string	 argument  with 1-place number x, where x is a
	      digit between 1 and 9.
       \$(xy  Macro or string argument with 2-digit number xy.
       \$[nexp]
	      Macro or string argument with  number  nexp,  where  nexp	 is  a
	      numerical expression evaluating to an integer ≥1.
       \$*    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.
       \\     reduces  to  a single backslash; useful to delay its interpreta‐
	      tion as escape character in copy mode.  For  a  printable	 back‐
	      slash,  use \e, or even better \[rs], to be independent from the
	      current escape character.
       \’     The acute accent ´; same as \(aa.	 Unescaped: apostrophe,	 right
	      quotation mark, single quote (ASCII 0x27).
       \`     The  grave accent `; same as \(ga.  Unescaped: left quote, back‐
	      quote (ASCII 0x60).
       \-     The - sign in the current font.
       \.     An uninterpreted dot (period), even at start of line.
       \%     Default optional hyphenation character.
       \!     Transparent line indicator.
       \?anything?
	      In a diversion, this will transparently embed  anything  in  the
	      diversion.   anything is read in copy mode.  See also the escape
	      sequences \!  and \?.
       \space Unpaddable space-size space character (no line break).
       \0     Digit width.
       \|     1/6 em narrow space character; zero width in nroff.
       \^     1/12 em half-narrow space character; zero width in nroff.
       \&     Non-printable, zero width character.
       \)     Like \& except that it behaves like a  character	declared  with
	      the  cflags request to be transparent for the purposes of end of
	      sentence recognition.
       \/     Increases the width of the preceding character so that the spac‐
	      ing  between  that character and the following character will be
	      correct if the following character is a roman character.
       \,     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.
       \~     Unbreakable space that stretches like a normal inter-word	 space
	      when a line is adjusted.
       \:     Inserts  a  zero-width  break point (similar to \% but without a
	      soft hyphen character).
       \newline
	      Ignored newline, for continuation lines.
       \{     Begin conditional input.
       \}     End conditional input.
       \(sc   The special character with 2-character name sc, see section Spe‐
	      cial Characters.
       \[name]
	      The named character with arbitrary length name name.
       \a     Non-interpreted leader character.
       \A’anything’
	      If  anything  is acceptable as a name of a string, macro, diver‐
	      sion, register, environment or font it expands to 1,  and	 to  0
	      otherwise.
       \b’abc...’
	      Bracket building function.
       \B’anything’
	      If  anything  is	acceptable  as	a  valid numeric expression it
	      expands to 1, and to 0 otherwise.
       \c     Interrupt text processing.
       \C’char’
	      The character called char; same as \[char],  but	compatible  to
	      other roff versions.
       \d     Forward (down) 1/2 em vertical unit (1/2 line in nroff).
       \D’charseq’
	      Draw  a  graphical element defined by the characters in charseq;
	      see groff info file for details.
       \e     Printable version of the current escape character.
       \E     Equivalent to an escape character, but  is  not  interpreted  in
	      copy-mode.
       \fF    Change to font with 1-character name or 1-digit number F.
       \fP    Switch back to previous font.
       \f(fo  Change to font with 2-character name or 2-digit number fo.
       \f[font]
	      Change  to  font with arbitrary length name or number expression
	      font.
       \f[]   Switch back to previous font.
       \Ff    Change to font family with 1-character name f.
       \F(fm  Change to font family with 2-character name fm.
       \F[fam]
	      Change to font family with arbitrary length name fam.
       \F[]   Switch back to previous font family.
       \g[reg]
	      Return format of	register  with	name  reg  suitable  for  .af.
	      Alternative forms \g(xy and \gx.
       \h’N’  Local horizontal motion; move right N (left if negative).
       \H’N’  Set height of current font to N.
       \k[reg]
	      Mark  horizontal	input  place in register with arbitrary length
	      name reg.	 Alternative forms \k(xy and \kx.
       \l’Nc’ Horizontal line drawing function (optionally using character c).
       \L’Nc’ Vertical line drawing function (optionally using character c).
       \m[color]
	      Change to color color.  Alternative forms \m(co and \mc.
       \m[]   Switch back to previous color.
       \M[color]
	      Change filling color for closed drawn objects  to	 color	color.
	      Alternative forms \M(co and \Mc.
       \M[]   Switch to previous fill color.
       \nr    The  numerical  value  stored  in the register variable with the
	      1-character name r.
       \n(re  The numerical value stored in the	 register  variable  with  the
	      2-character name re.
       \n[reg]
	      The  numerical  value stored in the register variable with arbi‐
	      trary length name reg.
       \N’n’  Typeset the character with code n in the current font,  no  spe‐
	      cial fonts are searched.	Useful for adding characters to a font
	      using the char request.
       \o’abc...’
	      Overstrike characters a, b, c, etc.
       \O0    Disable glyph output.  Mainly for internal use.
       \O1    Enable glyph output.  Mainly for internal use.
       \p     Break and spread output line.
       \r     Reverse 1 em vertical motion (reverse line in nroff).
       \R’name ±n’
	      The same as .nr name ±n.
       \s[±N] Set the point size to N scaled  points.	Note  the  alternative
	      forms  \s±[N], \s'±N', \s±'N', \s(±xy, \s±(xy, \s±x.  Same as ps
	      request.
       \S’N’  Slant output N degrees.
       \t     Non-interpreted horizontal tab.
       \u     Reverse (up) 1/2 em vertical motion (1/2 line in nroff).
       \v’N’  Local vertical motion; move down N (up if negative).
       \V[env]
	      The contents of the environment variable env.  Alternative forms
	      \V(xy and \Vx.
       \w’string’
	      The width of the character sequence string.
       \x’N’  Extra line-space function (negative before, positive after).
       \X’string’
	      Output string as device control function.
       \Y[name]
	      Output  string  variable	or  macro name uninterpreted as device
	      control function.	 Alternative forms \Y(xy and \Yx.
       \zc    Print c with zero width (without spacing).
       \Z’anything’
	      Print anything and then  restore	the  horizontal	 and  vertical
	      position; anything may not contain tabs or leaders.

       The  escape  sequences \e, \., \", \$, \*, \a, \n, \t, \g, and \newline
       are interpreted in copy mode.

       Escape sequences starting with \( or \[ do not represent single charac‐
       ter escape sequences, but introduce escape names with two or more char‐
       acters.

       If a backslash is followed by a character that does  not	 constitute  a
       defined escape sequence the backslash is silently ignored and the char‐
       acter maps to itself.

   Special Characters
       Common special characters are predefined by  escape  sequences  of  the
       form  \(xy  with	 characters x and y.  Some of these exist in the usual
       font while most of them are only available in the special font.	 Below
       you'll  find  a selection of the most important glyphs; a complete list
       can be found in groff_char(7).

	      \(bu   Bullet sign
	      \(co   Copyright
	      \(ct   Cent
	      \(dd   Double dagger
	      \(de   Degree
	      \(dg   Dagger
	      \(rs   Printable double quote
	      \(em   Em-dash
	      \(hy   Hyphen
	      \(rg   Registered sign
	      \(rs   Printable backslash character
	      \(sc   Section sign
	      \(ul   Underline character
	      \(==   Identical
	      \(>=   Larger or equal
	      \(<=   Less or equal
	      \(!=   Not equal
	      \(->   Right arrow
	      \(<-   Left arrow
	      \(+-   Plus-minus sign

   Strings
       Strings are defined by the ds request and can be retrieved  by  the  \*
       escape sequence.

       Strings	share  their  name  space  with macros.	 So strings and macros
       without arguments are roughly equivalent; it  is	 possible  to  call  a
       string  like  a	macro  and  vice-versa, but this often leads to unpre‐
       dictable results.  The following strings are predefined in groff.

       \*[.T]	 The name of the current output device as specified by the  -T
		 command line option.

REGISTERS
       Registers  are  variables that store a value.  In groff, most registers
       store numerical values (see section NUMERICAL EXPRESSIONS  above),  but
       some can also hold a string value.

       Each  register is given a name.	Arbitrary registers can be defined and
       set with the request nr register.

       The value stored in a register can be retrieved by the escape sequences
       introduced by \n.

       Most  useful  are  predefined registers.	 In the following the notation
       name is used to refer to a register called register name to make	 clear
       that we speak about registers.  Please keep in mind that the \n[] deco‐
       ration is not part of the register name.

   Read-only Registers
       The following registers have predefined values that should not be modi‐
       fied  by the user (usually, registers starting with a dot a read-only).
       Mostly, they provide information	 on  the  current  settings  or	 store
       results from request calls.

       \n[.$]	 Number of arguments in the current macro or string.
       \n[.a]	 Post-line  extra  line-space  most  recently  utilized	 using
		 \x’N’.
       \n[.A]	 Set to 1 in troff if option -A is used; always 1 in nroff.
       \n[.c]	 Current input line number.
       \n[.C]	 1 if compatibility mode is in effect, 0 otherwise.
       \n[.cdp]	 The depth of the last character added to the current environ‐
		 ment.	 It  is	 positive  if  the character extends below the
		 baseline.
       \n[.ce]	 The number of lines remaining to be centered, as set  by  the
		 ce request.
       \n[.cht]	 The  height  of the last character added to the current envi‐
		 ronment.  It is positive if the character extends  above  the
		 baseline.
       \n[.color]
		 1 if colors are enabled, 0 otherwise.
       \n[.csk]	 The  skew of the last character added to the current environ‐
		 ment.	The skew of a character is how far to the right of the
		 center of a character the center of an accent over that char‐
		 acter should be placed.
       \n[.d]	 Current vertical place in current diversion; equal to	regis‐
		 ter register nl.
       \n[.ev]	 The  name  or	number of the current environment (string-val‐
		 ued).
       \n[.f]	 Current font number.
       \n[.fam]	 The current font family (string-valued).
       \n[.fn]	 The current (internal) real font name (string-valued).
       \n[.fp]	 The number of the next free font position.
       \n[.g]	 Always 1 in GNU troff.	 Macros should use it to test if  run‐
		 ning under groff.
       \n[.h]	 Text base-line high-water mark on current page or diversion.
       \n[.H]	 Available horizontal resolution in basic units.
       \n[.hla]	 The current hyphenation language as set by the .hla request.
       \n[.hlc]	 The  number  of  immediately preceding consecutive hyphenated
		 lines.
       \n[.hlm]	 The maximum allowed number of consecutive  hyphenated	lines,
		 as set by the hlm request.
       \n[.hy]	 The current hyphenation flags (as set by the hy request).
       \n[.hym]	 The current hyphenation margin (as set by the hym request).
       \n[.hys]	 The current hyphenation space (as set by the hys request).
       \n[.i]	 Current ident.
       \n[.in]	 The indent that applies to the current output line.
       \n[.int]	 Positive if last output line contains \c.
       \n[.kern] 1 if pairwise kerning is enabled, 0 otherwise.
       \n[.l]	 Current line length.
       \n[.lg]	 The current ligature mode (as set by the lg request).
       \n[.linetabs]
		 The current line-tabs mode (as set by the linetabs request).
       \n[.ll]	 The line length that applies to the current output line.
       \n[.lt]	 The title length (as set by the lt request).
       \n[.n]	 Length of text portion on previous output line.
       \n[.ne]	 The  amount  of  space that was needed in the last ne request
		 that caused a trap to be sprung.  Useful in conjunction  with
		 register .trunc.
       \n[.ns]	 1 if in no-space mode, 0 otherwise.
       \n[.o]	 Current page offset.
       \n[.p]	 Current page length.
       \n[.pn]	 The  number  of  the  next page: either the value set by a pn
		 request, or the number of the current page plus 1.
       \n[.ps]	 The current pointsize in scaled points.
       \n[.psr]	 The last-requested pointsize in scaled points.
       \n[.pvs]	 The current post-vertical line spacing.
       \n[.rj]	 The number of lines to be right-justified as set  by  the  rj
		 request.
       \n[.s]	 Current point size as a decimal fraction.
       \n[.sr]	 The  last requested pointsize in points as a decimal fraction
		 (string-valued).
       \n[.t]	 Distance to the next trap.
       \n[.T]	 Set to 1 if option -T is used.
       \n[.tabs] A string representation of the current tab settings  suitable
		 for use as an argument to the ta request.
       \n[.trunc]
		 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
		 .ne.  In other words, at the point a trap is sprung, it  rep‐
		 resents  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 register .ne
		 register.
       \n[.ss]	 The value of the parameters set by the first argument of  the
		 ss request.
       \n[.sss]	 The value of the parameters set by the second argument of the
		 ss request.
       \n[.u]	 Equal to 1 bin fill mode and 0 in nofill mode.
       \n[.v]	 Current vertical line spacing.
       \n[.V]	 Available vertical resolution in basic units.
       \n[.vpt]	 1  if vertical position traps are enabled, 0 otherwise.
       \n[.w]	 Width of previous character.
       \n[.warn] The sum of the number codes of the  currently	enabled	 warn‐
		 ings.
       \n[.x]	 The major version number.
       \n[.y]	 The minor version number.
       \n[.Y]	 The revision number of groff.
       \n[.z]	 Name of current diversion.

   Writable Registers
       The following registers can be read and written by the user.  They have
       predefined default values, but these can be modified for customizing  a
       document.

       \n[%]	 Current page number.
       \n[c.]	 Current input line number.
       \n[ct]	 Character type (set by width function \w).
       \n[dl]	 Maximal width of last completed diversion.
       \n[dn]	 Height of last completed diversion.
       \n[dw]	 Current day of week (1-7).
       \n[dy]	 Current day of month (1-31).
       \n[hours] The number of hours past midnight.  Initialized at start-up.
       \n[hp]	 Current horizontal position at input line.
       \n[llx]	 Lower	left  x-coordinate  (in	 PostScript  units) of a given
		 PostScript image (set by .psbb).
       \n[lly]	 Lower left y-coordinate (in  PostScript  units)  of  a	 given
		 PostScript image (set by .psbb).
       \n[ln]	 Output line number.
       \n[minutes]
		 The  number of minutes after the hour.	 Initialized at start-
		 up.
       \n[mo]	 Current month (1-12).
       \n[nl]	 Vertical position of last printed text base-line.
       \n[rsb]	 Like register sb, but takes account of the heights and depths
		 of characters.
       \n[rst]	 Like register st, but takes account of the heights and depths
		 of characters.
       \n[sb]	 Depth of string below base line (generated by width  function
		 \w).
       \n[seconds]
		 The  number  of  seconds  after  the  minute.	Initialized at
		 start-up.
       \n[skw]	 Right skip width from the center of the last character in the
		 \w argument.
       \n[slimit]
		 If greater than 0, the maximum number of objects on the input
		 stack.	 If ≤0 there is no limit, i.e., recursion can continue
		 until virtual memory is exhausted.
       \n[ssc]	 The  amount  of  horizontal  space  (possibly	negative) that
		 should be added to the	 last  character  before  a  subscript
		 (generated by width function \w).
       \n[st]	 Height of string above base line (generated by width function
		 \w).
       \n[systat]
		 The return value of the system()  function  executed  by  the
		 last sy request.
       \n[urx]	 Upper	right  x-coordinate  (in  PostScript units) of a given
		 PostScript image (set by .psbb).
       \n[ury]	 Upper right y-coordinate (in PostScript  units)  of  a	 given
		 PostScript image (set by .psbb).
       \n[year]	 The current year (year 2000 compliant).
       \n[yr]	 Current  year	minus  1900.   For Y2K compliance use register
		 register year instead.

COMPATIBILITY
       The differences of the groff language in comparison to classical	 troff
       as defined by [CSTR #54] are documented in groff_diff(7).

       The  groff system provides a compatibility mode, see groff(1) on how to
       invoke this.

BUGS
       Report bugs to the groff bug mailing list ⟨bug-groff@gnu.org⟩.  Include
       a complete, self-contained example that will allow the bug to be repro‐
       duced, and say which version of groff you are using.

AUTHORS
       Copyright (C) 2000, 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 on your system, it is also available on-line at the GNU
       copyleft site ⟨http://www.gnu.org/copyleft/fdl.html⟩.

       This  document  is  part	 of  groff, the GNU roff distribution.	It was
       written by Bernd Warken ⟨bwarken@mayn.de⟩; it is maintained  by	Werner
       Lemberg ⟨wl@gnu.org⟩.

SEE ALSO
       The  main  source  of  information  for the groff language is the groff
       info(1) file.  Besides the gory details, it contains many examples.

       groff(1)
	      the usage of the groff program and pointers to the documentation
	      and availability of the groff system.

       groff_diff(7)
	      the  differences	of the groff language as compared to classical
	      roff.  This is the authoritative	document  for  the  predefined
	      language elements that are specific to groff.

       groff_char(7)
	      the predefined groff characters (glyphs).

       groff_font(5)
	      the specification of fonts and the DESC file.

       roff(7)
	      the  history  of	roff, the common parts shared by all roff sys‐
	      tems, and pointers to further documentation.

       [CSTR #54]
	      Nroff/Troff User's Manual by Osanna & Kernighan ⟨http://
	      cm.bell-labs.com/cm/cs/54.ps⟩ — the bible for classical troff.

Groff Version 1.18.1		   Nov	2003			      GROFF(7)
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