groff(7) — Linux manual page

Name | Description | groff

elements | Control characters | Line continuation | Numerical expressions | Control structures | Syntax reference conventions | Requests | Escape sequences | Identifiers | Strings | Registers | Hyphenation | Localization | Writing macros | Traps | Underlining | Compatibility | Debugging | Authors | See also | COLOPHON

groff(7)            Miscellaneous Information Manual            groff(7)

Name         top

       groff - GNU roff language reference

Description         top

       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 provides only short descriptions of roff language
       elements.  Groff: The GNU Implementation of troff, by Trent A.
       Fisher and Werner Lemberg, is the primary groff manual, and is
       written in Texinfo.  You can browse it interactively with “info
       groff”.

       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.

       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 spaces (but not tab characters) 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 is 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 ‘]’.
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 glyphs have a constant width anyway.

       Glyphs are visual representation forms of characters.  In groff,
       the distinction between those two elements is not always obvious
       (and a full discussion is beyond the scope of this man page).  A
       first approximation is that glyphs have a specific size and
       colour and are taken from a specific font; they can't be modified
       any more – characters are the input, and glyphs are the output.
       As soon as an output line has been generated, it no longer
       contains characters but glyphs.  In this man page, we use either
       ‘glyph’ or ‘character’, whatever is more appropriate.  A few
       characters commonly seen on keyboards are treated specially by
       roff languages and may not look correct in output; they are the
       (double) quotation mark ("), the apostrophe ('), the minus sign
       (-), the backslash (\), the caret or circumflex accent (^), the
       grave accent (`), and the tilde (~).  All are available if
       required; see groff_char(7).

       Moreover, there are some advanced roff elements.  A diversion
       stores (formatted) information into a macro for later usage.  See
       groff_tmac(5) for more details.  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
       Texinfo manual.

Control characters         top

       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).  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 apostrophe has two controlling tasks.  At the
              beginning of a line and in the conditional requests it is
              the no-break 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.  The
              no-break control character can be changed with the .c2
              request.

              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 do work).  In
              all other positions, it denotes a single quote or
              apostrophe character, depending on the output device's
              glyph repertoire.  groff provides a printable
              representation with the \(aq escape sequence.

       "      The double quote can be used to enclose arguments to
              macros and strings, but not requests.  In the .ds, .ds1,
              .as, and .as1 requests, a leading double quote in the
              second argument is stripped off, enabling the inclusion of
              leading space characters in the string definition or
              appendment.  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 behaviour 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 separate arguments in request
              invocations, macro calls, and string interpolations.  In
              text, they separate words.  Multiple adjacent space
              characters in text cause groff to attempt end-of-sentence
              detection on the preceding word (and trailing
              punctuation).  The amount of space between words and
              sentences is controlled by the .ss request.  When filling
              is enabled (the default), a line may be broken at a space.
              When adjustment is enabled and set to both margins (the
              default), inter-word spaces may be expanded to justify the
              line.  To get a space of definite width, use the escape
              sequences ‘\ ’ (this is the escape character followed by a
              space), \0, \|, \^, or \h; see section “Escape sequences”
              below.  An adjustable but non-breaking space is available
              with \~.

       newline
              In text, a newline puts an inter-word space onto the
              output and triggers end-of-sentence recognition on the
              preceding text.  See section “Line continuation” below.

       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.

Line continuation         top

       A backslash \ at the end of a line immediately followed by a
       newline suppresses the effects of that newline on the input.  The
       next input line thus retains the classification of its
       predecessor as a control or text line.  The \c escape sequence
       continues an output line.  Anything on the input line after \c is
       ignored except \R, which works as usual.  In contrast to
       \newline, a line after \c is treated as a new input line, so a
       control character is recognized at its beginning.  The visual
       results depend on whether filling is enabled.  An intervening
       control line that causes a break overrides \c, flushing out the
       pending output line in the usual way.  The register .int contains
       a positive value if the last output line was continued with \c;
       this datum is associated with the environment.

Numerical expressions         top

       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 (approx. width of
                        letter ‘m’)
              M         100th of an em
              n         en = em/2
              u         Basic unit for output device
              v         vee (vertical line space)
              s         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 provides the following additional 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 Texinfo manual.

Control structures         top

       groff has “if” and “while” control structures like other
       languages.  However, the syntax for grouping multiple input lines
       in the branches or bodies of these structures is unusual.

       They have a common form: the request name is (except for .el
       “else”) followed by a conditional expression cond-expr, and then
       the remainder of the line anything is interpreted as if it were
       an input line.  Any number of spaces between arguments to
       requests serves only to separate them; leading spaces in anything
       are therefore not seen.  anything effectively cannot be omitted;
       if cond-expr is true and anything is empty, the newline at the
       end of the control line is interpreted as a blank line (and
       therefore a blank text line).

       It is frequently desirable for a control structure to govern more
       than one request, call more than one macro, span more than one
       input line of text, or mix the foregoing.  The opening and
       closing brace escapes \{ and \} perform such grouping.  Brace
       escapes can be used outside of control structures, but when they
       are they have no meaning and produce no output.

       \{ should appear (after optional spaces and tabs) immediately
       subsequent to the request's conditional expression.  \} should
       appear on a line with other occurrences of itself as necessary to
       match \{ escapes.  It can be preceded by a control character,
       spaces, and tabs.  Input after a \} escape on the same line is
       only processed if all the preceding conditions to which the
       escapes correspond are true.  Furthermore, a \} closing the body
       of a .while request must be the last such escape on an input
       line.

   Conditional expressions
       In .if, .ie, and .while requests, in addition to the numeric
       expressions described above, several Boolean operators are
       available; the members of this expanded class are termed
       conditional expressions.

       A numerical expression expr is true if its value is positive.  In
       roff languages, negative values are false.  The truth values of
       other conditional expression operators are as shown below.

       cond-expr...   ...is true if...
       ──────────────────────────────────────────────────────────────────
            's1's2'   s1 produces the same formatted output as s2.
                c g   a glyph g is available.
                d m   a string, macro, diversion, or request m is
                      defined.
                  e   the current page number is even.
                F f   a font named f is available.
                m c   a color named c is defined.
                  n   the formatter is in nroff mode.
                  o   the current page number is odd.
                r n   a register named n is defined.
                S s   a font style named s is available.
                  t   the formatter is in troff mode.
                  v   n/a (historical artifact; always false).

       These operators can't be combined with others like “:” or “&”;
       only a leading “!” can be used to complement the result.  Spaces
       and tabs are optional immediately after the “c”, “d”, “F”, “m”,
       “r”, and “S” operators, but immediately after “!”, they cause the
       condition to evaluate false (this bizarre behavior maintains
       compatibility with AT&T troff).

Syntax reference conventions         top

       In the following request and escape sequence specifications, most
       argument names were chosen to be descriptive.  A few denotations
       may require introduction.

              c         denotes a single input character.
              font      a font either specified as a font name or a
                        numeric mounting position.
              anything  all characters up to the end of the line, to the
                        ending delimiter for the escape sequence, or
                        within \{ and \}.  Escape sequences may
                        generally be used freely in anything, except
                        when it is read in copy mode.
              n         is a numerical expression that evaluates to an
                        integer value.
              N         is an optionally-signed numerical expression.
              ±N        has three meanings, depending on its sign.

       If a numeric expression presented as ±N starts with a ‘+’ sign,
       an increment in the amount of of N is applied to the value
       applicable to the request or escape sequence.  If it starts with
       a ‘-’ sign, a decrement of magnitude N is applied instead.
       Without a sign, N replaces any existing value.  To assign a
       negative number, either prefix the expression with a zero or
       enclose it with parentheses.  If a prior value does not exist, an
       increment or decrement is applied as if to 0.

Requests         top

       In groff, identifier names, including those of requests, can be
       arbitrarily long.  No bracketing or marking of long names is
       needed in request invocation syntax.

       Most requests take one or more arguments.  Tabs are permitted
       after a request name, before its first argument (if any), but
       arguments themselves must be separated only by space characters.
       There is no inherent limit on argument length or quantity.

       Not all details of request behavior are outlined here.  Refer to
       the groff Texinfo manual or groff_diff(7).

   Request short reference
       .ab string
                 Write string to the standard error stream and exit with
                 failure status.
       .ad       Enable output line adjustment using mode stored in
                 \n[.j].
       .ad c     Enable output line adjustment in mode c (c=b,c,l,n,r).
                 Sets \n[.j].
       .af register c
                 Assign format c to register, where c is “i”, “I”, “a”,
                 “A”, or a sequence of decimal digits whose quantity
                 denotes the minimum width in digits to be used when the
                 register is interpolated.  “i” and “a” indicate Roman
                 numerals and base-26 Latin alphabetics, respectively,
                 in the lettercase specified.  The default is “0”.
       .aln new old
                 Create alias (additional name) new for existing number
                 register named old.
       .als new old
                 Create alias (additional name) new for existing
                 request, string, macro, or diversion old.
       .am macro Append to macro until .. is encountered.
       .am macro end
                 Append to macro until .end is called.
       .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.
       .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.
       .ami1 macro
                 Same as .ami but with compatibility mode switched off
                 during macro expansion.
       .ami1 macro end
                 Same as .ami but with compatibility mode switched off
                 during macro expansion.
       .as name [string]
                 Append string to the string name; no operation if
                 string is omitted.
       .as1 name [string]
                 Same as .as but with compatibility mode switched off
                 during string expansion.
       .asciify diversion
                 Unformat ASCII characters, spaces, and some escape
                 sequences in diversion.
       .backtrace
                 Write a backtrace of the input stack to the standard
                 error stream.  Also see the -b option of groff(1).
       .bd font N
                 Embolden font by N-1 units.
       .bd S font N
                 Embolden Special Font S when current font is font.
       .blm      Unset blank line macro (trap).  Restore default
                 handling of blank lines.
       .blm name Set blank line macro (trap) to name.
       .box      Stop directing output to current box diversion.
       .box name Divert output to name, omitting a partially collected
                 line.
       .boxa     Stop appending output to current box diversion.
       .boxa name
                 Divert output, appending it to name, omitting a
                 partially collected line.
       .bp       Eject current page and begin new page.
       .bp ±N    Eject current page; next page number ±N.
       .br       Line break.
       .brp      Break output line; adjust if applicable.
       .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 n c1 c2 ...
                 Assign properties encoded by the number n to characters
                 c1, c2, and so on.
       .ch name N
                 Change location of page location trap by moving macro
                 name to new location N, or by unplanting it altogether
                 if N absent.
       .char c anything
                 Define entity c as string anything.
       .chop object
                 Remove the last character from the macro, string, or
                 diversion named object.
       .class name c1 c2 ...
                 Define a (character) class name comprising the
                 characters or range expressions c1, c2, and so on.
       .close stream
                 Close the stream.
       .color    Enable colors.
       .color N  If N is zero disable colors, otherwise enable them.
       .composite from to
                 Map glyph name from to glyph name to while constructing
                 a composite glyph name.
       .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.
       .dei1 macro
                 Same as .dei but with compatibility mode switched off
                 during macro expansion.
       .dei1 macro end
                 Same as .dei but with compatibility mode switched off
                 during macro expansion.
       .device anything
                 Write anything to the intermediate output as a device
                 control function.
       .devicem name
                 Write contents of macro or string name uninterpreted to
                 the intermediate output as a device control function.
       .di       End current diversion.
       .di macro Divert to macro.  See groff_tmac(5) for more details.
       .do name ...
                 Interpret the string, request, diversion, or macro name
                 (along with any arguments) with compatibility mode
                 disabled.  Note that compatibility mode is restored (if
                 and only if it was active) when the expansion of name
                 is interpreted.
       .ds name [string]
                 Define a string variable name with contents string, or
                 as empty if string is omitted.
       .ds1 name [string]
                 Same as .ds but with compatibility mode switched off
                 during string expansion.
       .dt       Clear diversion trap.
       .dt N name
                 Set diversion trap to macro name at position N (default
                 scaling indicator v).
       .ec       Set escape character to ‘\’.
       .ec c     Set escape character to c.
       .ecr      Restore escape character saved with .ecs.
       .ecs      Save current escape character.
       .el anything
                 Interpret anything as if it were an input line if the
                 conditional expression of the corresponding .ie request
                 was false.
       .em name  Invoke macro name after the end of input.
       .eo       Unset escape character, turning off escape
                 interpretation.
       .ev       Pop environment stack, returning to previous one.
       .ev env   Push current environment onto stack and switch to env.
       .evc env  Copy environment env to the current one.
       .ex       Exit with successful status.
       .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 glyph to space.
       .fc a b   Set field delimiter to a and pad glyph to b.
       .fchar c anything
                 Define fallback character (or glyph) c as string
                 anything.
       .fcolor   Set fill color to previous fill color.
       .fcolor c Set fill color to c.
       .fi       Enable filling of output lines; a pending output line
                 is broken.  Sets \n[.u].
       .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.
       .fschar f c anything
                 Define fallback character (or glyph) c for font f as
                 string anything.
       .fspecial font
                 Reset list of special fonts for font to be empty.
       .fspecial font s1 s2 ...
                 When the current font is font, then the fonts s1, s2,
                 ... are 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.
       .fzoom font
                 Don't magnify font.
       .fzoom font zoom
                 Set zoom factor for font (in multiples of 1/1000th).
       .gcolor   Set glyph color to previous glyph color.
       .gcolor c Set glyph color to c.
       .hc       Reset the hyphenation character to \% (the default).
       .hc char  Change the hyphenation character to char.
       .hcode c1 code1 [c2 code2] ...
                 Set the hyphenation code of character c1 to code1, that
                 of c2 to code2, and so on.
       .hla lang Set the hyphenation language to lang.
       .hlm n    Set the maximum number of consecutive hyphenated lines
                 to n.
       .hpf pattern-file
                 Read hyphenation patterns from pattern-file.
       .hpfa pattern-file
                 Append hyphenation patterns from pattern-file.
       .hpfcode a b [c d] ...
                 Define mapping values for character codes in pattern
                 files read with the .hpf and .hpfa requests.
       .hw word ...
                 Define how each word is to be hyphenated, with each
                 hyphen “-” indicating a hyphenation point.
       .hy       Set automatic hyphenation mode to 1.
       .hy 0     Disable automatic hyphenation; same as .nh.
       .hy mode  Set automatic hyphenation mode to mode; see section
                 “Hyphenation” below.
       .hym      Set the (right) hyphenation margin to 0 (the default).
       .hym length
                 Set the (right) hyphenation margin to length (default
                 scaling indicator m).
       .hys      Set the hyphenation space to 0 (the default).
       .hys hyphenation-space
                 Suppress hyphenation of the line in adjustment modes
                 “b” or “n” if it can be justified by adding no more
                 than hyphenation-space extra space to each inter-word
                 space (default scaling indicator m).
       .ie cond-expr anything
                 If cond-expr is true, interpret anything as if it were
                 an input line, otherwise skip to a corresponding .el
                 request.
       .if cond-expr anything
                 If cond-expr is true, then interpret anything as if it
                 were an input line.
       .ig       Ignore text until .. is encountered.
       .ig end   Ignore text until .end is called.
       .in       Change to previous indentation value.
       .in ±N    Change indentation according to ±N (default scaling
                 indicator m).
       .it n name
                 Set an input line trap, calling macro name, after the
                 next n lines lines of text input have been read.
       .itc n name
                 As .it, but don't count lines interrupted with \c.
       .kern     Enable pairwise kerning.
       .kern n   If n is zero, disable pairwise kerning, otherwise
                 enable it.
       .lc       Remove leader repetition glyph.
       .lc c     Set leader repetition glyph to c (default: “.”).
       .length reg anything
                 Compute the number of characters of anything and store
                 the count in the number register reg.
       .linetabs Enable line-tabs mode (calculate tab positions relative
                 to beginning of output line).
       .linetabs 0
                 Disable line-tabs mode.
       .lf N     Set input line number to N.
       .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 length 6.5i,
                 default scaling indicator m).
       .lsm      Unset the leading space macro (trap).  Restore default
                 handling of lines with leading spaces.
       .lsm name Set the leading space macro (trap) to name.
       .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 glyph off.
       .mc c     Print glyph c after each text line at actual distance
                 from right margin.
       .mc c N   Set margin glyph to c and distance to N from right
                 margin (default scaling indicator m).
       .mk [register]
                 Mark current vertical position in register, or in an
                 internal register used by .rt if no argument.
       .mso file As .so, except that file is sought in the tmac
                 directories.
       .msoquiet file
                 As .mso, but no warning is emitted if file does not
                 exist.
       .na       Disable output line adjustment.
       .ne       Need a one-line vertical space.
       .ne N     Need N vertical space (default scaling indicator v).
       .nf       Disable filling of output lines; a pending output line
                 is broken.  Clears \n[.u].
       .nh       Disable automatic hyphenation; same as “.hy 0”.
       .nm       Number mode off.
       .nm ±N [M [S [I]]]
                 In line number mode, set number, multiple, spacing, and
                 indentation.
       .nn       Do not number next line.
       .nn N     Do not number next N lines.
       .nop anything
                 Interpret anything as if it were an input line.
       .nr register ±N [M]
                 Define or modify register using ±N with auto-increment
                 M.
       .nroff    Make the built-in conditions n true and t false.
       .ns       Turn on no-space mode.
       .nx       Immediately jump to end of current file.
       .nx filename
                 Immediately continue processing with file file.
       .open stream filename
                 Open filename for writing and associate the stream
                 named 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 is
                 stripped off).
       .pc       Reset page number character to ‘%’.
       .pc c     Page number character.
       .pev      Report the state of the current environment followed by
                 that of all other environments to the standard error
                 stream.
       .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       Report, to the standard error stream, the names and
                 sizes in bytes of defined macros, strings, and
                 diversions.
       .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    Set/increase/decrease the point size to/by N scaled
                 points (a non-positive resulting point size is set to
                 1 u); also see \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      Report names and positions of all page location traps
                 to the standard error stream.
       .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 entities c1, c2, ...
       .rd prompt
                 Read insertion.
       .return   Return from a macro.
       .return anything
                 Return twice, namely from the macro at the current
                 level and from the macro one level higher.
       .rfschar f c1 c2 ...
                 Remove the font-specific definitions of glyphs c1, c2,
                 ... for font f.
       .rj n     Right justify the next n input lines.
       .rm name  Remove request, macro, diversion, or string name.
       .rn old new
                 Rename request, macro, diversion, or string old to new.
       .rnn reg1 reg2
                 Rename register reg1 to reg2.
       .rr ident Remove name of number register ident.
       .rs       Restore spacing; turn no-space mode off.
       .rt       Return (upward only) to vertical position marked by .mk
                 on the current page.
       .rt ±N    Return (upward only) to specified distance from the top
                 of the page (default scaling indicator v).
       .schar c anything
                 Define global fallback character (or glyph) c as string
                 anything.
       .shc      Reset the soft hyphen glyph to \[hy].
       .shc c    Set the soft hyphen glyph 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 file  Replace the request's control line with the contents of
                 file, “sourcing” it.
       .soquiet file
                 As .so, but no warning is emitted if file does not
                 exist.
       .sp       Skip one line vertically.
       .sp N     Space vertical distance N up or down according to sign
                 of N (default scaling indicator v).
       .special  Reset global list of special fonts to be empty.
       .special s1 s2 ...
                 Fonts s1, s2, etc. are special and are searched for
                 glyphs not in the current font.
       .spreadwarn
                 Toggle the spread warning on and off (the default)
                 without changing its value.
       .spreadwarn N
                 Emit a break warning if the additional space inserted
                 for each space between words in an output line adjusted
                 to both margins is larger than or equal to N.  A
                 negative N is treated as 0.  The default scaling
                 indicator is m.  At startup, .spreadwarn is inactive
                 and N is 3 m.
       .ss N     Set minimal inter-word spacing to N 12ths of the space
                 width of the current font.
       .ss N M   As .ss N, and set additional inter-sentence spacing to
                 M 12ths of the space width of the current font.
       .stringdown stringvar
                 Replace each byte in the string named stringvar with
                 its lowercase version.
       .stringup stringvar
                 Replace each byte in the string named stringvar with
                 its uppercase version.
       .sty n style
                 Associate style with font position n.
       .substring str start [end]
                 Replace the string named str with its substring bounded
                 by the indices start and end, inclusive.  Negative
                 indices count backwards from the end of the string.
       .sv       Save 1 v of vertical space.
       .sv N     Save the vertical distance N for later output with .os
                 request (default scaling indicator v).
       .sy command-line
                 Execute program command-line.
       .ta n1 n2 ... nn T r1 r2 ... rn
                 Set tabs at positions n1, n2, ..., nn, then set tabs at
                 nn+m×rn+r1 through nn+m×rn+rn, where m increments from
                 0, 1, 2, ... to the output line length.  Each
                 n argument can be prefixed with a “+” to place the tab
                 stop ni at a distance relative to the previous, n(i-1).
                 Each argument ni or ri can be suffixed with a letter to
                 align text within the tab column bounded by tab stops
                 i and i+1; “L” for left-aligned (the default), “C” for
                 centered, and “R” for right-aligned.
       .tc       Remove tab repetition glyph.
       .tc c     Set tab repetition glyph to c (default: none).
       .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 stderr.
       .tm1 anything
                 Print anything on stderr, allowing leading whitespace
                 if anything starts with " (which is 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 uses 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 conditions t true and n false.
       .uf font  Set underline font to font (to be switched to by .ul).
       .ul N     Underline (italicize in troff mode) N input lines.
       .unformat diversion
                 Unformat space characters and tabs in diversion,
                 preserving font information.
       .vpt      Enable vertical position traps.
       .vpt 0    Disable vertical position traps.
       .vs       Change to previous vertical base line spacing.
       .vs ±N    Set vertical base line spacing to ±N (default scaling
                 indicator p).
       .warn     Enable all warnings.
       .warn n   Set warnings code to n.
       .warnscale si
                 Set scaling indicator used in warnings to si.
       .wh N     Remove active trap at vertical position N; a negative
                 value is measured upward from page bottom.
       .wh N name
                 Plant trap, calling macro name when page location N is
                 reached or passed; a negative value is measured upward
                 from page bottom.  Any active trap already present at N
                 is replaced.
       .while cond-expr anything
                 Evaluate cond-expr, and repeatedly execute anything
                 unless and until cond-expr evaluates false.
       .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 recognize.  They enclose their
       code between a pair of characteristic macros.

               ┌─────────────┬─────────────────┬────────────────┐
               │preprocessor │   start macro   │    end macro   │
               ├─────────────┼─────────────────┼────────────────┤
               │    chem     .cstart     .cend      │
               │    eqn      .EQ       .EN       │
               │    grap     .G1       .G2       │
               │    grn      .GS       .GE       │
               │   ideal     .IS       .IE       │
               │             │                 │      .IF       │
               │    pic      .PS       .PE       │
               │   refer     .R1       .R2       │
               │   soelim    nonenone      │
               │    tbl      .TS       .TE       │
               ├─────────────┼─────────────────┼────────────────┤
               │ glilypond   .lilypond start .lilypond stop │
               │   gperl     .Perl start   .Perl stop   │
               │  gpinyin    .pinyin start  .pinyin stop  │
               └─────────────┴─────────────────┴────────────────┘
       The ‘ideal’ preprocessor is not available in groff yet.

Escape sequences         top

       Whereas requests must occur on control lines, escape sequences
       can occur intermixed with text and appear in arguments to
       requests and macros (and sometimes other escape sequences).  An
       escape sequence (or simply “escape”) is introduced by the escape
       character, a backslash “\” (but see the .ec request).  The next
       character identifies the escape's function.  Escapes vary in
       length.  Some take an argument, and of those, some have different
       syntactical forms for a one-character, two-character, or
       arbitrary-length argument.  Others accept only an arbitrary-
       length argument.  In the former convention, a one-character
       argument follows the function character immediately, an opening
       parenthesis “(” introduces a two-character argument (no closing
       parenthesis is used), and an argument of arbitrary length is
       enclosed in brackets “[]”.  In the latter convention, the user
       selects a delimiter character; the neutral apostrophe “'” is a
       popular choice and shown in this document.  Some characters
       cannot be used as delimiters; see section “Escapes” in the groff
       Texinfo manual for details.  A few escapes are idiosyncratic, and
       support both of the foregoing conventions (“\s”), designate their
       own terminating character (“\?”), consume input until the next
       newline (“\!”, “\"”, “\#”), or support an additional modifier
       character (“\s” again).

       Escape sequences serve a variety of purposes.  Widespread uses
       include commenting the source document; changing the font style;
       setting the point size; interpolating special characters, number
       registers, and strings into the text; and placing or suppressing
       break and hyphenation points.  As with requests, use of escapes
       in source documents may interact poorly with a macro package you
       use; consult its documentation to learn of “safe” escapes or
       alternative facilities it provides to achieve the desired result.

       If the escape character is followed by a character that does not
       identify a defined operation, the escape character is ignored
       (producing a diagnostic of the “escape” warning type, which is
       not enabled by default) and the following character is processed
       normally.

   Escape short reference
       The escape sequences \", \#, \$, \*, \a, \e, \n, \t, \g, \V, and
       \newline are interpreted even in copy mode.

       \"     Comment.  Everything up to the end of the line is ignored.
       \#     Comment.  Everything up to and including the next newline
              is ignored.
       \*s    Interpolate string with one-character name s.
       \*(st  Interpolate string with two-character name st.
       \*[string]
              Interpolate string with name string (of arbitrary length).
       \*[string arg1 arg2 ...]
              Interpolate string with name string (of arbitrary length),
              taking arg1, arg2, ... as arguments.
       \$0    Interpolate name by which currently-executing macro was
              invoked.
       \$n    Interpolate macro or string parameter numbered n (1≤n≤9).
       \$(nn  Interpolate macro or string parameter numbered nn
              (01≤nn≤99).
       \$[nnn]
              Interpolate macro or string parameter numbered nnn
              (nnn≥1).
       \$*    Interpolate concatenation of all macro or string
              parameters, separated by spaces.
       \$@    Interpolate concatenation of all macro or string
              parameters, with each surrounded by double quotes and
              separated by spaces.
       \$^    Interpolate concatenation of all macro or string
              parameters as if they were arguments to the .ds request.
       \'     Translates to \[aa], the acute accent special character.
       \`     Translates to \[ga], the grave accent special character.
       \-     Translates to \[-], the minus sign special character.
       \_     Translates to \[ul], the underline special character.
       \%     Control hyphenation.
       \!     Transparent line.  The remainder of the input line is
              interpreted (1) when the current diversion is read; or (2)
              if in the top-level diversion, by the output driver.
       \?anything\?
              Transparently embed anything, read in copy mode, in a
              diversion.
       \space Unbreakable, non-adjustable word space.
       \~     Unbreakable, adjustable space.
       \0     Unbreakable digit-width space.
       \|     Unbreakable 1/6 em (“thin”) space glyph; zero-width in
              nroff.
       \^     Unbreakable 1/12 em (“hair”) space glyph; zero-width in
              nroff.
       \&     Non-printing input break.
       \)     Non-printing input break, transparent to end-of-sentence
              recognition.
       \/     Apply italic correction.  Use between an immediately
              adjacent oblique glyph on the left and an upright glyph on
              the right.
       \,     Apply left italic correction.  Use between an immediately
              adjacent upright glyph on the left and an oblique glyph on
              the right.
       \:     Non-printing break point (similar to \%, but never
              produces a hyphen glyph).
       \newline
              Continue current input line on the next.
       \{     Begin conditional input.
       \}     End conditional input.
       \(gl   Interpolate glyph with two-character name gl.
       \[glyph]
              Interpolate glyph with name glyph (of arbitrary length).
       \[base-glyph comp1 comp2 ...]
              Interpolate composite glyph constructed from base-glyph
              and components comp1, comp2, and so on.
       \[charnnn]
              Interpolate glyph of eight-bit encoded character nnn,
              where 0≤nnn≤255.
       \[unnnn[n[n]]]
              Interpolate glyph of Unicode character with code point
              nnnn[n[n]] in uppercase hexadecimal.
       \[ubase-glyph[_combining-component]...]
              Interpolate composite glyph from Unicode character base-
              glyph and combining-components.
       \a     In copy mode, interpolate leader character.
       \A'anything'
              Interpolate 1 if anything is an acceptable identifier for
              a string, macro, diversion, register, environment, or
              font, and 0 otherwise.
       \b'abc...'
              Build bracket: stack glyphs a, b, c... vertically.
       \B'anything'
              Interpolate 1 if anything is a valid numeric expression,
              and 0 otherwise.
       \c     Continue output line at next input line.
       \C'glyph'
              As \[glyph], but compatible with other troff
              implementations.
       \d     Move downward ½ vee (½ line in nroff).
       \D'anything'
              Send anything to the output device as a drawing command;
              see groff_out(5).
       \e     Interpolate escape character.
       \E     As \e, but not interpreted in copy mode.
       \fF    Change to font or style with one-character name or one-
              digit position F.
       \fP    Switch to previous font or style.
       \f(ft  Change to font with two-character name or two-digit
              position ft.
       \f[font]
              Change to font with arbitrarily long name or position
              font.
       \f[]   Switch to previous font or style.
       \Ff    Change to font family with one-character name f.
       \F(fm  Change to font family with two-character name fm.
       \F[fam]
              Change to font family with arbitrarily long name fam.
       \F[]   Switch to previous font family.
       \gr    Interpolate format of register with one-character name r.
       \g(rg  Interpolate format of register with two-character name rg.
              rg.
       \g[reg]
              Interpolate format of register with arbitrarily long name
              reg.
       \h'N'  Horizontally move N ens (or specified units) right (left
              if negative).
       \H'N'  Set height of current font to N scaledpoints (or specified
              units).
       \kr    Mark horizontal position in one-character register name r.
       \k(rg  Mark horizontal position in two-character register
              name rg.
       \k[reg]
              Mark horizontal position in register with arbitrarily long
              name reg.
       \l'N[g]'
              Draw horizontal line of length N ems (or specified units),
              optionally using glyph g.
       \L'N[g]'
              Draw vertical line of length N vees (or specified units),
              optionally using glyph g.
       \mc    Change drawing color to that with one-character name c.
       \m(cl  Change drawing color to that with two-character name cl.
       \m[color]
              Change drawing color to that with arbitrarily long
              name color.
       \m[]   Switch to previous drawing color.
       \Mc    Change fill color to that with one-character name c.
       \M(cl  Change fill color to that with two-character name cl.
       \M[color]
              Change fill color to that with arbitrarily long
              name color.
       \M[]   Switch to previous fill color.
       \nr    Interpolate value stored in register with one-character
              name r.
       \n(rg  Interpolate value stored in register with two-character
              name rg.
       \n[reg]
              Interpolate value stored in register with arbitrarily long
              name reg.
       \N'n'  Interpolate glyph with index n in the current font.
       \o'abc...'
              Overstrike glyphs a, b, c, and so on.
       \O0    At the outermost suppression level, disable glyph emission
              to the output driver.
       \O1    At the outermost suppression level, enable glyph emission
              to the output driver.
       \O2    At the outermost suppression level, enable glyph emission
              to the output driver and write to the standard error
              stream the page number and four bounding box registers
              enclosing glyphs written since the previous \O escape
              sequence.
       \O3    Begin a nested suppression level.
       \O4    End a nested suppression level.
       \O[5Pfilename]
              At the outermost suppression level, write filename to the
              standard error stream; P indicates the position of an
              image and must be one of l, r, c, or i (left, right,
              centered, inline).
       \p     Break output line at next word boundary; adjust if
              applicable.
       \r     Move “in reverse” (upward) 1 vee (reverse linefeed in
              nroff).
       \R'name ±N'
              Set, increment, or decrement register name by N.
       \s±N   Set/increase/decrease the point size to/by N scaled
              points.  N must be a single digit; 0 restores the previous
              point size.  (In compatibility mode only, a non-zero N
              must be in the range 4–39.)  Otherwise, as .ps request.
       \s(±N
       \s±(N  Set/increase/decrease the point size to/by N scaled
              points; N is a two-digit number ≥1.  As .ps request.
       \s[±N]
       \s±[N]
       \s'±N'
       \s±'N' Set/increase/decrease the point size to/by N scaled
              points.  As .ps request.
       \S'N'  Slant output glyphs by N degrees; the direction of text
              flow is positive.
       \t     In copy mode, interpolate tab character.
       \u     Move upward ½ vee (½ line in nroff).
       \v'N'  Vertically move N vees (or specified units) down (up if
              negative).
       \Ve    Interpolate contents of environment variable with one-
              character name e.
       \V(ev  Interpolate contents of environment variable with two-
              character name ev.
       \V[env]
              Interpolate contents of environment variable with
              arbitrarily long name env.
       \w'anything'
              Interpolate width of anything, formatted in a dummy
              environment.
       \x'N'  Increase required line space by N vees (or specified
              units; negative before, positive after).
       \X'anything'
              Send anything to the output device as a control command;
              see groff_out(5).
       \Yn    Send interpolation of string or macro with one-character
              name n to the output device as a control command.
       \Y(nm  Send interpolation of string or macro with two-character
              name nm to the output device as a control command.
       \Y[name]
              Send interpolation of string or macro with arbitrarily
              long name name to the output device as a control command.
       \zc    Output glyph c without advancing the print position, as if
              it were zero-width.
       \Z'anything'
              Print anything and then restore the horizontal and
              vertical position; anything must not contain tabs or
              leaders.

Identifiers         top

       An identifier is a label for an object of syntactical importance
       like a register, a name (macro, string, or diversion), an
       environment, a font, a style, or a glyph, comprising a sequence
       of one or more characters with the following exceptions.

       •      Spaces, tabs, or newlines.

       •      Invalid input characters; these are certain control
              characters (from the sets “C0 Controls” and “C1 Controls”
              as Unicode describes them).  When troff encounters one in
              an identifier, it produces a warning diagnostic of type
              “input” (see section “Warnings” in troff(1)).

              On a machine using the ISO 646, 8859, or 10646 character
              encodings, invalid input characters are 0x00, 0x08, 0x0B,
              0x0D0x1F, and 0x800x9F.

              On an EBCDIC host, they are 0x000x01, 0x08, 0x09, 0x0B,
              0x0D0x14, 0x170x1F, and 0x300x3F.

              Some of these code points are used by troff internally,
              making it non-trivial to extend the program to cover
              Unicode or other character encodings that use characters
              from these ranges.  (Consider what happens when a C1
              control 0x800x9F is necessary as a continuation byte in a
              UTF-8 sequence.}

              Invalid characters are removed during parsing; an
              identifier “foo”, followed by an invalid character,
              followed by “bar” is treated as “foobar.

Strings         top

       groff has string variables primarily for user convenience.  Only
       one string is predefined by the language.

       \*[.T]    Contains the name of the output driver (for example,
                 “utf8” or “pdf).

       The .ds request creates a string with a specified name and
       contents and the \* escape dereferences its name, retrieving the
       contents.  Dereferencing an undefined string name defines it as
       empty.

       The .as request is similar to .ds but appends to a string instead
       of redefining it.  If .as is called with only one argument, no
       operation is performed (beyond dereferencing it).

       The .ds1 request defines a string such that compatibility mode is
       off when the string is later interpolated.  To be more precise, a
       compatibility save input token is inserted at the beginning of
       the string, and a compatibility restore input token at the end.
       Likewise, the .as1 request is similar to .as, but compatibility
       mode is switched off when the appended portion of the string is
       later interpolated.

       Caution: Unlike other requests, the second argument to these
       requests consumes the remainder of the input line, including
       trailing spaces.  It is good style to end string definitions (and
       appendments) with a comment, even an empty one, to prevent
       unwanted space from creeping into them during source document
       maintenance.

       To store leading space in a string, start it with a double quote.
       A double quote is special only in that position; double quotes in
       any other location are included in the string (the effects of
       escape sequences notwithstanding).

       Strings, macros, and diversions share a name space.  Internally,
       the same mechanism is used to store them.

       Several requests exist to perform rudimentary string operations.
       Strings can be queried (.length) and modified (.chop, .substring,
       .stringup, .stringdown), and their names can be manipulated
       through renaming, removal, and aliasing (.rn, .rm, .als).

Registers         top

       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 .nr request.

       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 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 are
       read-only).  Mostly, they provide information on the current
       settings or store results from request calls.

       \n[$$]    The process ID of troff.
       \n[.$]    Number of arguments in the current macro or string.
       \n[.a]    Post-line extra line-space most recently utilized using
                 \x.
       \n[.A]    Set to 1 in troff if option -A is used; always 1 in
                 nroff.
       \n[.b]    The emboldening offset while .bd is active.
       \n[.br]   Within a macro, set to 1 if macro called with the
                 ‘normal’ control character, and to 0 otherwise.
       \n[.c]    Current input line number.
       \n[.C]    1 if compatibility mode is in effect, 0 otherwise.
                 Always 0 in a .do request; see register .cp below.
       \n[.cdp]  The depth of the last glyph added to the current
                 environment.  It is positive if the glyph 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 glyph added to the current
                 environment.  It is positive if the glyph extends above
                 the baseline.
       \n[.color]
                 1 if colors are enabled, 0 otherwise.
       \n[.cp]   Within a .do request, the saved value of compatibility
                 mode (see register .C above).
       \n[.csk]  The skew of the last glyph added to the current
                 environment.  The skew of a glyph is how far to the
                 right of the center of a glyph the center of an accent
                 over that glyph should be placed.
       \n[.d]    Current vertical place in current diversion; equal to
                 register nl.
       \n[.ev]   The name or number of the current environment (string-
                 valued).
       \n[.f]    Current font number.
       \n[.F]    The name of the current input file (string-valued).
       \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.  Use to test if running under
                 groff.
       \n[.h]    Text baseline high-water mark on page or in diversion.
       \n[.H]    Number of basic units per horizontal unit of output
                 device resolution.
       \n[.height]
                 The current font height as set with \H.
       \n[.hla]  The hyphenation language in the current environment.
       \n[.hlc]  The count of immediately preceding consecutive
                 hyphenated lines in the current environment.
       \n[.hlm]  The maximum number of consecutive hyphenated lines
                 allowed in the current environment.
       \n[.hy]   The automatic hyphenation mode in the current
                 environment.
       \n[.hym]  The hyphenation margin in the current environment.
       \n[.hys]  The hyphenation space adjustment threshold in the
                 current environment.
       \n[.i]    Current indentation.
       \n[.in]   The indentation that applies to the current output
                 line.
       \n[.int]  Positive if last output line contains \c.
       \n[.j]    Adjustment mode encoded as an integer.  Do not
                 interpret or perform arithmetic on its value.
       \n[.k]    The current horizontal output position (relative to the
                 current indentation).
       \n[.kern] 1 if pairwise kerning is enabled, 0 otherwise.
       \n[.l]    Current line length.
       \n[.L]    The current line spacing setting as set by .ls.
       \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[.m]    The current drawing color (string-valued).
       \n[.M]    The current background color (string-valued).
       \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[.nm]   1 if output line numbering is enabled (even if
                 temporarily suppressed), 0 otherwise.
       \n[.ns]   1 if in no-space mode, 0 otherwise.
       \n[.o]    Current page offset.
       \n[.O]    The suppression nesting level (see \O).
       \n[.p]    Current page length.
       \n[.P]    1 if the current page is being printed, 0 otherwise (as
                 determined by the -o command-line option).
       \n[.pe]   1 during page ejection, 0 otherwise.
       \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 point size in scaled points.
       \n[.psr]  The last-requested point size in scaled points.
       \n[.pvs]  The current post-vertical line spacing.
       \n[.R]    The number of unused number registers.  Always 10000 in
                 GNU troff.
       \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[.slant]
                 The slant of the current font as set with \S.
       \n[.sr]   The last requested point size in points as a decimal
                 fraction (string-valued).
       \n[.ss]   Size of minimal inter-word spacing in twelfths of the
                 space width of the current font.
       \n[.sss]  Size of additional inter-sentence spacing in twelfths
                 of the space width of the current font.
       \n[.sty]  The current font style (string-valued).
       \n[.t]    Distance to the next vertical position 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 an .ne request, minus the amount of
                 vertical motion produced by .ne.  Useful in conjunction
                 with the register .ne.
       \n[.u]    Equal to 1 if filling is enabled, 0 otherwise.
       \n[.U]    1 in unsafe mode and 0 otherwise.
       \n[.v]    Current vertical line spacing.
       \n[.V]    Number of basic units per vertical unit of output
                 device resolution.
       \n[.vpt]  1 if vertical position traps are enabled, 0 otherwise.
       \n[.w]    Width of previous glyph.
       \n[.warn] The sum of the number codes of the currently enabled
                 warnings.
       \n[.x]    The major version number of the running troff
                 formatter.
       \n[.y]    The minor version number of the running troff
                 formatter.
       \n[.Y]    The revision number of the running troff formatter.
       \n[.z]    Name of current diversion.
       \n[.zoom] Zoom factor for current font (in multiples of 1/1000th;
                 zero if no magnification).

   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[lsn]   The count of leading spaces on an input line.
       \n[lss]   The amount of horizontal space corresponding to the
                 leading spaces on an input line.
       \n[minutes]
                 The number of minutes after the hour.  Initialized at
                 start-up.
       \n[mo]    Current month (1–12).
       \n[nl]    Current vertical position.
       \n[opmaxx]
       \n[opmaxy]
       \n[opminx]
       \n[opminy]
                 These four registers mark the top left and bottom right
                 hand corners of a box which encompasses all written
                 glyphs.  They are reset to -1 by \O0 or \O1.
       \n[rsb]   Like register sb, but takes account of the heights and
                 depths of glyphs.
       \n[rst]   Like register st, but takes account of the heights and
                 depths of glyphs.
       \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 glyph 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 glyph 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.
       \n[yr]    The current year minus 1900.

Hyphenation         top

       When filling, groff hyphenates words as needed at user-specified
       and automatically determined hyphenation points.  Explicitly
       hyphenated words such as “mother-in-law” are eligible for
       breaking after each of their hyphens.  The hyphenation
       character \% and non-printing break point \: escapes may be used
       to control the hyphenation and breaking of individual words.  The
       .hw request sets user-defined hyphenation points for specified
       words at any subsequent occurrence.  Otherwise, groff determines
       hyphenation points automatically by default.

       Several requests influence automatic hyphenation.  Because
       conventions vary, a variety of hyphenation modes is available to
       the .hy request; these determine whether hyphenation will apply
       to a word prior to breaking a line at the end of a page (more or
       less; see below for details), and at which positions within that
       word automatically determined hyphenation points are permissible.
       The default is “1” for historical reasons, but this is not an
       appropriate value for the English hyphenation patterns used by
       groff; localization macro files loaded by troffrc and macro
       packages often override it.

       0      disables hyphenation.

       1      enables hyphenation except after the first and before the
              last character of a word.

       The remaining values “imply” 1; that is, they enable hyphenation
       under the same conditions as “.hy 1”, and then apply or lift
       restrictions relative to that basis.

       2      disables hyphenation of the last word on a page.
              (Technically, hyphenation is prevented if the next page
              location trap is closer than the next line of text would
              be.  groff automatically inserts an implicit page location
              trap at the end of each page to cause a page transition.
              Users or macro packages can set such traps explicitly to
              prevent hyphenation of the last word in a column in multi-
              column page layouts or before floating figures or tables.
              See section “Traps” below.)

       4      disables hyphenation before the last two characters of a
              word.

       8      disables hyphenation after the first two characters of a
              word.

       16     enables hyphenation before the last character of a word.

       32     enables hyphenation after the first character of a word.

       Apart from value 2, restrictions imposed by the hyphenation mode
       are not respected for words whose hyphenations have been
       explicitly specified with the hyphenation character (“\%” by
       default) or the .hw request.

       The nonzero values above are additive.  For example, value 12
       causes groff to hyphenate neither the last two nor the first two
       characters of a word.  Some values cannot be used together
       because they contradict; for instance, values 4 and 16, and
       values 8 and 32.  As noted, it is superfluous to add 1 to any
       nonzero even mode.

       The places within a word that are eligible for hyphenation are
       determined by language-specific data (.hla, .hpf, and .hpfa) and
       lettercase relationships (.hcode and .hpfcode).  Furthermore,
       hyphenation of a word might be suppressed because too many
       previous lines have been hyphenated (.hlm), the line has not
       reached a certain minimum length (.hym), or the line can instead
       be adjusted with up to a certain amount of additional inter-word
       space (.hys).

Localization         top

       The set of hyphenation patterns is associated with the
       hyphenation language set by the .hla request.  The .hpf request
       is usually invoked by a localization file loaded by the troffrc
       file.  By default, troffrc loads the localization file for
       English.  (As of groff 1.23.0, localization files for Czech (cs),
       German (de), English (en), French (fr), Japanese (ja), Swedish
       (sv), and Chinese (zh) exist.)  For Western languages, the
       localization file sets the hyphenation mode and loads hyphenation
       patterns and exceptions.  It also (re-)defines translatable
       strings and macros that packages use to handle localization
       tasks, such as formatting the calendar date.

Writing macros         top

       The .de request defines a macro replacing the definition of any
       existing request, macro, string, or diversion of the same name.
       troff stores subsequent lines to an internal buffer in “copy
       mode” (see below).  If the optional second argument is not
       specified, the macro definition ends with the control line “..”
       (two dots).  Alternatively, a second argument names a macro whose
       call syntax ends the definition; this “end macro” is then called
       normally.  Spaces or tabs are permitted after the first control
       character in the line containing this ending token.  A tab
       immediately after the token prevents is recognition as the end of
       a macro definition.  Macro definitions can be nested; this
       requires use of unique end macros for each nested definition or
       escaping of the line with the ending token.  An end macro need
       not be defined until it is called.  This fact enables a nested
       macro definition to begin inside one macro and end inside
       another.

       Variants of .de that disable compatibility mode and/or indirect
       the names of the macros being defined or ending the definition
       through a string are available as .de1, .dei, and .dei1.
       Existing macro definitions can be appended to with .am, .am1,
       .ami, and .ami1.  The .als, .rm, and .rn requests create an alias
       of, remove, and rename a macro, respectively.  .return stops the
       execution of a macro immediately, returning to the enclosing
       context.

   Parameters
       Macro calls and string parameters can be accessed using the \$
       escapes.  The \n[.$] read-only register stores the count of
       parameters available to a macro or string; its value can be
       changed by the .shift request, which dequeues parameters from the
       current list.  The \$0 escape sequence interpolates the name by
       which a macro was called.  Applying string interpolation to a
       macro does not change this name.

   Copy mode
       When troff processes certain requests, most importantly those
       which define or append to a macro or string, it does so in copy
       mode: it copies the characters of the definition into a dedicated
       storage region, interpolating the escape sequences \n, \g, \$,
       \*, and \V normally; interpreting \newline immediately;
       discarding comments \" and \#; interpolating the current leader,
       escape, or tab character with \a, \e, and \t, respectively; and
       storing all other escape sequences in an encoded form.  The
       complement of copy mode—a roff formatter's behavior when not
       defining or appending to a macro, string, or diversion—where all
       macros are interpolated, requests invoked, and valid escape
       sequences processed immediately upon recognition, can be termed
       interpretation mode.

       The escape character, \ by default, escapes itself.  Thus you can
       control whether a given \n, \g, \$, \*, or \V escape sequence is
       interpreted at the time the macro containing it is defined, or
       later when the macro is called.

       You can think of \\ as a “delayed” backslash; it is the escape
       character followed by a backslash from which the escape character
       has removed its special meaning.  Consequently, \\ is not an
       escape sequence in the usual sense.  In any escape sequence \X
       that troff does not recognize, the escape character is ignored
       and X is output, with two exceptions, \\ being one.  The other is
       \., which escapes the control character.  It is used to permit
       nested macro definitions to end without a named macro call to
       conclude them.  Without a syntax for escaping the control
       character, this would not be possible.  roff documents should not
       use the \\ or \. tokens outside of copy mode; they serve only to
       obfuscate the input.  Use \e to obtain the escape character,
       \[rs] to obtain a backslash glyph, and \& before “.” and “'”
       where troff expects them as control characters if you mean to use
       them literally.

       Macro definitions can be nested to arbitrary depth.  Each escape
       character is interpreted twice—once in copy mode, when the macro
       is defined, and once in interpretation mode, when it is executed.
       This fact leads to exponential growth in the number of escape
       characters required to delay interpolation of \n, \g, \$, \*, and
       \V at each nesting level.  An alternative is to use \E, which
       represents an escape character that is not interpreted in copy
       mode.  Because \. is not a true escape sequence, we can't use \E
       to keep “..” from ending a macro definition prematurely.  If the
       multiplicity of backslashes complicates maintenance, use end
       macros.

Traps         top

       Traps are locations in the output, or conditions on the input
       that, when reached or fulfilled, cause a specified macro to be
       called.  These traps can occur at a given location on the page
       (.wh, .ch); at a given location in the current diversion
       (.dt)—together, these are known as vertical position traps, which
       can be disabled and re-enabled (.vpt); at a blank line (.blm); at
       a line with leading space characters (.lsm); after a certain
       number of input lines (.it, .itc); or at the end of input (.em).
       Macros called by traps have no arguments.  Setting a trap is also
       called planting.  It is also said that a trap is sprung if the
       associated macro is executed.

       Registers associated with trap management include vertical
       position trap enablement status (\n[.vpt]), distance to the next
       trap (\n[.t]), amount of needed (.ne-requested) space that caused
       the most recent vertical position trap to be sprung (\n[.ne]),
       amount of needed space truncated from the amount requested
       (\n[.trunc]), page ejection status (\n[.pe]), and leading space
       count (\n[.lsn]) with its corresponding amount of motion
       (\n[.lss]).

Underlining         top

       In the RUNOFF language, the underlining was quite easy.  But in
       roff this is much more difficult.

   Underlining with .ul
       There exists a groff request .ul (see above) that can underline
       the next or further source lines in nroff, but in troff it
       produces only a font change into italic.  So this request is not
       really useful.

   Underlining with .UL from ms
       In the ‘ms’ macro package in tmac/s.tmac groff_ms(7), there is
       the macro .UL.  But this works only in troff, not in nroff.

   Underlining macro definitions
       So one can use the italic nroff idea from .ul and the troff
       definition in ms for writing a useful new macro, something like
              .de UNDERLINE
              . ie n \\$1\f[I]\\$2\f[P]\\$3
              . el \\$1\Z'\\$2'\v'.25m'\D'l \w'\\$2'u 0'\v'-.25m'\\$3
              ..
       If doclifter(1) makes trouble, change the macro name UNDERLINE
       into some 2-letter word, like Ul.  Moreover, change the form of
       the font escape from \f[P] to \fP.

   Underlining without macro definitions
       If one does not want to use macro definitions, e.g., when
       doclifter gets lost, use the following:
              .ds u1 before
              .ds u2 in
              .ds u3 after
              .ie n \*[u1]\f[I]\*[u2]\f[P]\*[u3]
              .el \*[u1]\Z'\*[u2]'\v'.25m'\D'l \w'\*[u2]'u 0'\v'-.25m'\*[u3]
       When using doclifter, it might be necessary to change syntax
       forms such as \[xy] and \*[xy] to those supported by AT&T troff:
       \*(xy and \(xy, and so on.

       Then these lines could look like
              .ds u1 before
              .ds u2 in
              .ds u3 after
              .ie n \*[u1]\fI\*(u2\fP\*(u3
              .el \*(u1\Z'\*(u2'\v'.25m'\D'l \w'\*(u2'u 0'\v'-.25m'\*(u3

       The result looks like
              before _i_n after

   Underlining with overstriking \z and \(ul
       There is another possibility for underlining by using
       overstriking with \zc (print c with zero width without spacing)
       and \(ul (underline character).  This produces the underlining of
       1 character, both in nroff and in troff.

       For example the underlining of a character say t looks like
       \z\[ul]t or \z\(ult

       Longer words look then a bit strange, but a useful mode is to
       write each character into a whole own line.  To underlines the 3
       character part "tar" of the word "start":
              before s\
              \z\[ul]t\
              \z\[ul]a\
              \z\[ul]r\
              t after
       or
              before s\
              \z\(ult\
              \z\(ula\
              \z\(ulr\
              t after

       The result looks like
              before s_t_a_rt after

Compatibility         top

       The differences between the roff language recognized by GNU troff
       and that of AT&T troff, as well as the device, font, and device-
       independent intermediate output formats described by CSTR #54 are
       documented in groff_diff(7).

       groff provides an AT&T compatibility mode; see groff(1).

Debugging         top

       groff is not the easiest language to debug, in part thanks to its
       design features of recursive interpolation and multi-stage
       pipeline processing.  Nevertheless there exist several features
       useful for troubleshooting.

       Preprocessors use the .lf request to preserve the identities of
       line numbers and names of input files.  groff emits a variety of
       error diagnostics and supports several categories of warning; the
       output of these can be selectively suppressed with .warn (and see
       the -E, -w, and -W options of troff(1)).  Backtraces can be
       automatically produced when errors or warnings occur (the -b
       option of troff(1)) or generated on demand (.backtrace).  .tm,
       .tmc, and .tm1 can be used to emit customized diagnostic messages
       or for instrumentation while troubleshooting.  .ex and .ab cause
       early termination with successful and error exit codes
       respectively, to halt further processing when continuing would be
       fruitless.  The state of the formatter can be examined with
       requests that write lists of defined macros, strings, and
       diversions (.pm); environments (.pev), registers (.pnr), and page
       location traps (.ptr) to the standard error stream.

Authors         top

       This document was written by Bernd Warken ⟨groff-bernd.warken-72@
       web.de⟩.

See also         top

       Groff: The GNU Implementation of troff, by Trent A. Fisher and
       Werner Lemberg, is the primary groff manual.  You can browse it
       interactively with “info groff”.

       “Troff User's Manual” by Joseph F. Ossanna, 1976 (revised by
       Brian W. Kernighan, 1992), AT&T Bell Laboratories Computing
       Science Techical Report No. 54, widely called simply “CSTR #54”,
       documents the language, device and font description file formats,
       and device-independent output format referred to collectively in
       groff documentation as “AT&T troff”.

       “A Typesetter-independent TROFF” by Brian W. Kernighan, 1982,
       AT&T Bell Laboratories Computing Science Techical Report No. 97
       (CSTR #97), provides additional insights into the device and font
       description file formats and device-independent output format.

       groff(1)
              is the preferred interface to the groff system; it manages
              the pipeline that carries a source document through
              preprocessors, the troff formatter, and an output driver
              to viewable or printable form.  It also exhaustively lists
              all of the man pages provided with the GNU roff system.

       groff_char(7)
              discusses character encoding issues, escape sequences that
              produce glyphs, and enumerates groff's predefined special
              character escapes.

       groff_diff(7)
              covers the differences between the GNU troff formatter,
              its device and font description file formats, its device-
              independent output format, and those of AT&T troff, whose
              design it re-implements.

       groff_font(5)
              describes the formats of the files that describe devices
              (DESC) and fonts.

       groff_tmac(5)
              surveys macro packages provided with groff, describes how
              documents can take advantage of them, offers guidance on
              writing macro packages and using diversions, and includes
              historical information on macro package naming
              conventions.

       roff(7)
              presents a detailed history of roff systems and summarizes
              concepts common to them.

COLOPHON         top

       This page is part of the groff (GNU troff) project.  Information
       about the project can be found at 
       ⟨http://www.gnu.org/software/groff/⟩.  If you have a bug report
       for this manual page, see ⟨http://www.gnu.org/software/groff/⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-08-23.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

groff 1.23.0.rc1.1101-d1263-di2r6tyAugust 2021                     groff(7)

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