groff

GROFF(7)               Miscellaneous Information Manual               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
       background of the groff system.

       This document gives only short descriptions of the predefined roff
       language 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
       modified by escape sequences, which are recognized by a leading
       backslash ‘\’.  These are in-line or even in-word formatting elements
       or functions.  Some of these take arguments separated by single quotes
       “'”, others are regulated by a length encoding introduced by an open
       parenthesis ‘(’ 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
              precise, \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
       formatting 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
       herself 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
       counterpart.  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
       condition 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
              different 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
              separator in some functional escape sequences (but any pair of
              characters not part of the argument will work).  In all other
              positions, 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
              double quote in the argument will be stripped off, making
              everything 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 representation 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
              calculations.  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
              characters.  Continuation lines can be specified by an escaped
              newline, 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
       values 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
       expressions:

              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
       bracketing 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
       chosen to be descriptive.  Only the following denotations need
       clarification.

              c         denotes a single character.
              font      a font either specified as a font name or a font
                        number.
              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
                 register macro until .. is encountered.
       .ami macro end
                 Append to a macro indirectly.  macro and end are string
                 registers 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
                 components 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
                 indicator 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
                 environment.  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
                 indicator 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
                 scaling 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
                 characters 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 ’leftcenterright
                 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
                 character translation.
       .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 \!.
       .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
                 information 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
                 scaling 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
       separation 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
       functions and system related tasks, the 2-letter names following the \(
       construct are used for special characters predefined by the roff
       system.  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
              interpretation as escape character in copy mode.  For a
              printable backslash, 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 \(ga.  Unescaped: left quote,
              backquote (ASCII 0x60).
       \-     The - sign in the current font.
       \.     An uninterpreted dot (period), even at start of line.
       \%     Default optional hyphenation character.
       \!     Transparent line indicator.
       \?anything?
              In a diversion, this will transparently embed anything in the
              diversion.  anything is read in copy mode.  See also the escape
              sequences \!  and \?.
       \space Unpaddable space-size space character (no line break).
       \0     Digit width.
       \|     1/6 em narrow space character; zero width in nroff.
       \^     1/12 em half-narrow space character; zero width in nroff.
       \&     Non-printable, zero width character.
       \)     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
              spacing 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
              Special 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,
              diversion, 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’NLocal horizontal motion; move right N (left if negative).
       \H’NSet 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’NcHorizontal line drawing function (optionally using character c).
       \L’NcVertical 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
              arbitrary length name reg.
       \N’nTypeset the character with code n in the current font, no
              special 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’NSlant output N degrees.
       \t     Non-interpreted horizontal tab.
       \u     Reverse (up) 1/2 em vertical motion (1/2 line in nroff).
       \v’NLocal 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’NExtra 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
       character escape sequences, but introduce escape names with two or more
       characters.

       If a backslash is followed by a character that does not constitute a
       defined escape sequence the backslash is silently ignored and the
       character 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
       unpredictable 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[]
       decoration is not part of the register name.

   Read-only Registers
       The following registers have predefined values that should not be
       modified 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
                 environment.  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
                 environment.  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
                 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.
       \n[.d]    Current vertical place in current diversion; equal to
                 register register nl.
       \n[.ev]   The name or number of the current environment (string-
                 valued).
       \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
                 running 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
                 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 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
                 warnings.
       \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
       reproduced, 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
       Documentation 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
              systems, 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 1.18.1.1           29 June 2002                         GROFF(7)