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GROFF !!!GROFF NAME DESCRIPTION GROFF ELEMENTS CONTROL CHARACTERS NUMERICAL EXPRESSIONS CONDITIONS REQUESTS ESCAPE SEQUENCES REGISTERS WARNINGS COMPATIBILITY BUGS AUTHOR SEE ALSO ---- !!NAME groff - a short reference for the GNU roff language !!DESCRIPTION ''groff'' stands for ''GNU roff'' and is the free implementation of the roff type-setting system. See roff(7) for a survey and the background of the groff system. This document gives only short descriptions of the predefined roff language elements as used in groff. Both the classical features and the groff extensions are provided. Historically, the ''roff language'' was called ''troff''. ''groff'' is compatible with the classical system and provides proper extensions. So in GNU, the terms ''roff'', ''troff'', and ''groff language'' could be used as synonyms. However ''troff'' slightly tends to refer more to the classical aspects, whereas ''groff'' emphasizes the GNU extensions, and ''roff'' is the general term for the language. This file is only a short version of the complete documentation that is found in the ''groff'' info(1) file, which contains more detailed, actual, and concise information. The general syntax for writing groff documents is relatively easy, but writing extensions to the roff language can be a bit harder. The roff language is line-oriented. There are only two kinds of lines, control lines and text lines. The control lines start with a control character, by default a period ``.'' or a single quote ``'''; all other lines are text lines. __Control lines__ represent commands, optionally with arguments. They have the following syntax. The leading control character can be followed by a command name; arguments, if any, are separated by blanks from the command name and among themselves, for example, .command_name arg1 arg2 For indentation, any number of space or tab characters can be inserted between the leading control character and the command name, but the control character must be on the first position of the line. __Text lines__ represent the parts that will be printed. They can be modified by escape sequences, which are recognized by a leading backslash . These are in-line or even in-word formatting elements or functions. Some of these take arguments separated by single quotes ``''', others are regulated by a length encoding introduced by an open parenthesis ( or enclosed in brackets [[ and ]. The roff language provides flexible instruments for writing language extension, such as macros. When interpreting macro definitions, the roff system enters a special operating mode, called the __copy mode__. The copy mode behavior can be quite tricky, but there are some rules that ensure a safe usage. 1. Printable backslashes must be denoted as e. To be more precise, e represents the current escape character. To get a backslash glyph, use 2. Double all backslashes. 3. Begin all text lines with the special non-spacing character This does not produce the most efficient code, but it should work as a first measure. For better strategies, see the groff info file and groff_tmac(5). Reading roff source files is easier, just reduce all double backslashes to a single one in all macro definitions. !!GROFF ELEMENTS The roff language elements add formatting information to a text file. The fundamental elements are predefined commands and variables that make roff a full-blown programming language. There are two kinds of roff commands, possibly with arguments. __Requests__ are written on a line of their own starting with a dot . or a ``''', whereas __Escape sequences__ are in-line functions and in-word formatting elements starting with a backslash . The user can define her own formatting commands using the .de request. These commands are called __macros__, but they are used exactly like requests. Macro packages are pre-defined sets of macros written in the groff language. A user's possibilities to create escape sequences herself is very limited, only special characters can be mapped. The groff language provides several kinds of variables with different interfaces. There are pre-defined variables, but the user can define her own variables as well. __String__ variables store character sequences. They are set with the .ds request and retrieved by the * escape sequences. __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__ is everywhere available, but on text devices, it is displayed as an underlined Roman font. For the graphical output devices, there exist constant-width pendants of these font, __CR__, __CI__, and __CB__. On text devices, all characters have a constant width anyway. Moreover, there are some advanced roff elements. A __diversion__ stores information into a macro for later usage. A __trap__ is a positional condition like a certain number of lines from page top or in a diversion or in the input. Some action can be prescribed to be run automatically when the condition is met. More detailed information can be found in the groff info file. !!CONTROL CHARACTERS There is a small set of characters that have a special controlling task in certain conditions. . A dot is only special at the beginning of a line or after the condition in the requests .if, .ie, .el, and .while. There it is the control character that introduces a request (or macro). The special behavior can be delayed by using the . escape. By using the .cc request, the control character can be set to a different character, making the dot . a non-special character. In all other positions, it just means a dot character. In text paragraphs, it is advantageous to start each sentence at a line of its own. ' The single quote has two controlling tasks. At the beginning of a line and in the conditional requests it is the non-breaking control character. That means that it introduces a request like the dot, but with the additional property that this request doesn't cause a linebreak. By using the .c2 request, the non-break control character can be set to a different character. As a second task, it is the most commonly used argument separator in some functional escape sequences (but any pair of characters not part of the argument will work). In all other positions, it denotes the single quote or apostrophe character. Groff provides a printable representation with the escape sequence. The double quote is used to enclose arguments in requests and macros. In the .ds and .as requests, a leading double quote in the argument will be stripped off, making everything else afterwards the string to be defined (enabling leading whitespace). The escaped double quote \( \ 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 ( The open parenthesis is only special in escape sequences when introducing an escape name or argument consisting of exactly two characters. In groff, this behavior can be replaced by the [[] construct. [[ The opening bracket is only special in groff escape sequences; there it is used to introduce a long escape name or long escape argument. Otherwise, it is non-special, e.g. in macro calls. ] The closing bracket is only special in groff escape sequences; there it terminates a long escape name or long escape argument. Otherwise, it is non-special. space Space characters are only functional characters. They separate the arguments in requests or macros, and the words in text lines. They are subject to groff's horizontal spacing calculations. To get a defined space width, escape sequences like \ (this is the escape character followed by a space), |, ^, or h should be used. newline In text paragraphs, newlines mostly behave like space characters. Continuation lines can be specified by an escaped newline, i.e., by specifying a backslash \ as the last character of a line. tab If a tab character occurs during text the interpreter makes a horizontal jump to the next pre-defined tab position. There is a sophisticated interface for handling tab positions. !!NUMERICAL EXPRESSIONS A __numerical value__ is a signed or unsigned integer or float with or without an appended scale indicator. A __scale indicator__ is a one-character abbreviation for a unit of measurement. A number followed by a scale indicator signifies a size value. By default, numerical values do not have a scale indicator, i.e., they are normal numbers. The roff language defines the following scale indicators. __Numerical expressions__ are combinations of the numerical values defined above with the arithmetical operators +, -, *, /, % (''modulo''), the comparative operators == (this is the same as =), ''and''), : (''or''), ! (''not''), and the parentheses ( and ). Moreover, ''groff'' added the following operators for numeri- cal expressions: For details see the groff info file. !!CONDITIONS __Conditions__ occur in tests raised by the .if, .ie, and the .while requests. The following table characterizes the different types of conditions. !!REQUESTS This section provides a short reference for the predefined requests. In groff, request and macro names can be arbi- trarily long. No bracketing or marking of long names is needed. Most requests take one or more arguments. The arguments are separated by space characters (no tabs!); there is no inherent limit for their length or number. An argument can be enclosed by a pair of double quotes: This is very handy if an argument contains space characters, e.g., arg with space denotes a single argument. Some requests have optional arguments with a different be- haviour. Not all of these details are outlined here. Re- fer to the groff info file for all details. In the following request specifications, most argument names were chosen to be descriptive. Only the following denotations need clarification. If an expression defined as N starts with a + sign the resulting value of the expression will be added to an al- ready existing value inherent to the related request, e.g. adding to a number register. If the expression starts with a - the value of the expression will be subtracted from the request value. Without a sign, N replaces the existing value directly. To assign a negative number either prepend 0 or enclose the negative number in parentheses. __REQUEST SHORT REFERENCE__ . Empty line, ignored. Useful for structuring documents. .\( Complete line is a comment. .ab string Print string on standard error, exit program. .ad Begin line adjustment for output lines in cur- rent adjust mode. .ad c Start line adjustment in mode c (c=l,r,b,n). .af register c Assign format c to register (c=l,i,I,a,A). .aln alias register Create alias name for register. .als alias object Create alias name for request, string, macro, or diversion object. .am macro Append to macro until .. is called. .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. .as stringvar anything Append anything to stringvar. .asciify diversion Unformat ASCII characters, spaces, and some es- cape sequences in diversion. .backtrace Print a backtrace of the input on stderr. .bd font N Embolden font by N-1 units. .bd S font N Embolden Special Font S when current font is font. .blm Unset the blank line macro. .blm macro Set the blank line macro to macro. .box End current diversion. .box macro Divert to macro, omitting a partially filled line. .boxa End current diversion. .boxa macro Divert and append to macro, omitting a partially filled line. .bp Eject current page and begin new page. .bp N Eject current page; next page number N. .br Line break. .brp Break and spread output line. Same as p. .break Break out of a while loop. .c2 Reset no-break control character to ``'''. .c2 c Set no-break control character to c. .cc Reset control character to .. .cc c Set control character to c. .ce Center the next input line. .ce N Center following N input lines. .cf filename Copy contents of file filename unprocessed to stdout or to the diversion. .cflags mode c1 c2 ... Treat characters c1, c2, ... according to mode number. .ch trap N Change trap location to N. .char c anything Define character c to string anything. .chop object Chop the last character off macro, string, or diversion object. .close stream Close the stream. .continue Finish the current iteration of a while loop. .cp Enable compatibility mode. .cp N If ''N'' is zero disable compatibility mode, other- wise 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 called. .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. .dei macro Define or redefine a macro whose name is con- tained in the string register macro until .. is called. .dei macro end Define or redefine a macro indirectly. macro and end are string registers whose contents are interpolated for the macro name and the end macro, respectively. .di End current diversion. .di macro Divert to macro. .do name Interpret .name with compatibility mode dis- abled. .ds stringvar anything Set stringvar to anything. .dt N trap Set diversion trap to position N (default scale indicator v). .ec Reset escape character to . .ec c Set escape character to c. .ecr Restore escape character saved with .ecs. .ecs Save current escape character. .el anything Else part for if-else (.ie) request. .em macro The macro will be run after the end of input. .eo Turn off escape character mechanism. .ev Switch to previous environment. .ev env Push down environment number or name env and switch to it. .evc env Copy the contents of environment env to the cur- rent environment. No pushing or popping. .ex Exit from roff processing. .fam Return to previous font family. .fam name Set the current font family to name. .fc Disable field mechanism. .fc a Set field delimiter to a and pad character to space. .fc a b Set field delimiter to a and pad character to b. .fi Fill output lines. .fl Flush output buffer. .fp n font Mount font on position n. .fp n internal external Mount font with long external name to short in- ternal name on position n. .fspecial font s1 s2... When the current font is font, then the fonts s1, s2, ... will be special. .ft Return to previous font. Same as fP. .ft font Change to font name or number font; same as f[[font] escape sequence. .ftr font1 font2 Translate font1 to font2. .hc Remove additional hyphenation indicator charac- ter. .hc c Set up additional hyphenation indicator charac- ter c. .hcode c1 code1 c2 code2 ... Set the hyphenation code of character c1 to code1, that of c2 to code2, etc. .hla lang Set the current hyphenation language to lang. .hlm n Set the maximum number of consecutive hyphenated lines to n. .hpf file Read hyphenation patterns from file. .hw words List of words with exceptional hyphenation. .hy N Switch to hyphenation mode N. .hym n Set the hyphenation margin to n (default scale indicator m). .hys n Set the hyphenation space to n. .ie cond anything If cond then anything else goto .el. .if cond anything If cond then anything; otherwise do nothing. .ig Ignore text until .. is called. .ig end Ignore text until .end. .in Change to previous indent value. .in N Change indent according to N (default scale in- dicator m). .it N trap Set an input-line count trap at position N. .kern Enable pairwise kerning. .kern n If n is zero, disable pairwise kerning, other- wise enable it. .lc Remove leader repetition character. .lc c Set leader repetition character to c. .length register anything Write the length of the string anything in reg- ister. .linetabs Enable line-tabs mode (i.e., calculate tab posi- tions relative to output line). .linetabs n If n is zero, disable line-tabs mode, otherwise enable it. .lf N file Set input line number to N and filename to file. .lg N Ligature mode on if N. .ll Change to previous line length. .ll N Set line length according to N (default size 6.5i, default scale indicator m). .ls Change to the previous value of additional in- tra-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 scale indicator m). .mc Margin character off. .mc c Print character c after each text line at actual distance from right margin. .mc c N Set margin character to c and distance to N from right margin (default scale indicator m). .mk register Mark current vertical position in register. .mso file The same as the .so request except that ''file'' is searched in the tmac directories. .na No output-line adjusting. .ne Need a one-line vertical space. .ne N Need N vertical space (default scale indica- tor v). .nf No filling or adjusting of output-lines. .nh No hyphenation. .nm Number mode off. .nm N M S I In line number mode, set number, multiple, spac- ing, and indent. .nn Do not number next line. .nn N Do not number next N lines. .nop anything Always execute anything. .nr register N M Define or modify register using N with auto-in- crement M. .nroff Make the built-in condition __n__ true and __t__ false. .ns Turn no-space mode on. .nx filename Next 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. .pc Reset page number character to %. .pc c Page number character. .pi program Pipe output to program (nroff only). .pl Set page length to default 11i. The current page length is stored in .p. .pl N Change page length to N (default scale indica- tor v). .pm Print macro names and sizes (number of blocks of 128 bytes). .pm t Print only total of sizes of macros (number of 128 bytes blocks). .pn N Next page number N. .pnr Print the names and contents of all currently defined number registers on stderr. .po Change to previous page offset. The current page offset is available in .o. .po N Page offset N. .ps Return to previous point-size. .ps N Point size; same as s[[N]. .psbb filename Get the bounding box of a !PostScript image file- name. .pso command This behaves like the .so request except that input comes from the standard output of command. .ptr Print the names and positions of all traps (not including input line traps and diversion traps) on stderr. .rchar c1 c2... Remove the definitions of characters c1, c2, ... .rd prompt Read insertion. .return Return from a macro. .rj n Right justify the next n input lines. .rm name Remove request, macro, or string name. .rn old new Rename request, macro, or string old to new. .rnn reg1 reg2 Rename register reg1 to reg2. .rr register Remove register. .rs Restore spacing; turn no-space mode off. .rt N Return ''(upward only)'' to marked vertical place (default scale indicator v). .shc Reset soft hyphen character to .shc c Set the soft hyphen character to c. .shift n In a macro, shift the arguments by n positions. .so filename Include source file. .sp Skip one line vertically. .sp N Space vertical distance N up or down according to sign of N (default scaling indicator v). .special s1 s2 ... Fonts s1, s2, etc. are special and will be searched for characters not in the current font. .ss N Space-character size set to N/12 of the spacewidth in the current font. .ss N M Space-character size set to N/12 and sentence space size set to M/12 of the spacewidth in the current font (=1/3 em). .sty n style Associate style with font position n. .substring register n1 n2 Replace the string in register with the sub- string defined by the indices n1 and n2. .sv Save 1v of vertical space. .sv N Save the vertical distance N for later output with .os request. .sy command-line Execute program command-line. .ta T N Set tabs after every position that is a multiple of N (default scaling indicator m). .ta n1 n2 ... nn T r1 r2 ... rn Set tabs at positions n1, n2, ..., nn, then set tabs at nn+r1, nn+r2, ..., nn+rn, then at nn+rn+r1, nn+rn+r2, ..., nn+rn+rn, and so on. .tc Remove tab repition character. .tc c Set tab repetition character to c. .ti N Temporary indent next line (default scaling in- dicator m). .tkf font s1 n1 s2 n2 Enable track kerning for font. .tl leftcenterright Three-part title. .tm anything Print anything on terminal (UNIX standard mes- sage output). .tm1 anything Print anything on terminal (UNIX standard mes- sage output), allowing leading whitespace if anything starts with (which will be stripped off). .tmc anything Similar to .tm1 without emitting a final new- line. .tr abcd.... Translate a to b, c to d, etc. on output. .trf filename Transparently output the contents of file file- name. .trnt abcd.... This is the same as the .tr request except that the translations do not apply to text that is transparently throughput into a diversion with !. .troff Make the built-in condition __t__ true and __n__ false. .uf font Underline font set to font (to be switched to by .ul). .ul N Underline (italicize in troff) N input lines. .unformat diversion Unformat space characters and tabs, preserving font information in diversion. .vpt n Enable vertical position traps if n is non-zero, disable them otherwise. .vs Change to previous vertical base line spacing. .vs N Set vertical base line spacing to N. Default value is 12p. .warn n Set warnings code to n. .wh N trap Set location trap; negative means from page bot- tom. .while cond anything While condition cond is true, accept anything as input. .write stream anything Write anything to the stream named stream. Besides these standard groff requests, there might be fur- ther macro calls. They can originate from a macro package (see roff(7) for an overview) or from a preprocessor. Preprocessor macros are easy to be recognized. They en- close their code into a pair of characteristic macros. !!ESCAPE SEQUENCES Escape sequences are in-line language elements usually in- troduced by a backslash \ and followed by an escape name and sometimes by a required argument. Input processing is continued directly after the escaped character or the ar- gument resp. without an intervening separation character. So there must be a way to determine the end of the escape name and the end of the argument. This is done by enclosing names (escape name and arguments consisting of a variable name) by a pair of brackets [[name] and constant arguments (number expressions and characters) by apostrophes (ASCII 0x27) like ''constant''. There are abbreviations for short names. Two character escape names can be specified by an opening parenthesis like without a closing counterpart. And all one-character names different from the special characters [[ and ( can even be specified without a marker in the form c. Constant arguments of length 1 can omit the marker apos- trophes, too, but there is no two-character analogue. While 1-character escape sequences are mainly used for in-line functions and system related tasks, the 2-letter names following the construct are used for special characters predefined by the roff system. Names with more than two characters [[name] mostly denote user defined named characters (see the .char request). __SINGLE CHARACTER ESCAPES__ \( Beginning of a comment. Everything up to the end of the line is ignored. # Everything up to and including the next newline is ignored. This is interpreted in copy mode. This is like \( *s The string stored in the string variable with 1-character name s. *(st The string stored in the string variable with 2-character name st. *[[stringvar] The string stored in the string variable with arbi- trary length name stringvar. $0 The name by which the current macro was invoked. The .als request can make a macro have more than one name. $x Macro argument with 1-place number x, where x is a digit between 1 and 9. $(xy Macro argument with 2-digit number xy. $[[nexp] Macro argument with number nexp, where nexp is a numerical expression evaluating to an integer 1. $* In a macro, the concatenation of all the arguments separated by spaces. $@ In a macro, the concatenation of all the arguments with each surrounded by double quotes, and separat- ed by spaces. \ reduces to a single backslash; useful to delay its interpretation as escape character in copy mode. For a printable backslash, use e. \ The acute accent ; same as Unescaped: apos- trophe, right quotation mark, single quote (ASCII 0x27). ` The grave accent ; same as Unescaped: left quote, backquote (ASCII 0x60). - The - sign in the current font. . An uninterpreted dot (period), even at start of line. % Default optional hyphenation character. ! Transparent line indicator. ?anything__?__ In a diversion, this will transparently embed any- thing in the diversion. anything is read in copy mode. See also the escape sequences ! and ?. space Unpaddable space-size space character (no line break). 0 Digit width. | 1/6 em narrow space character; zero width in nroff. ^ 1/12 em half-narrow space character; zero width in nroff. Non-printable, zero width character. ) Like / Increases the width of the preceding character so that the spacing between that character and the following character will be correct if the follow- ing character is a roman character. , Modifies the spacing of the following character so that the spacing between that character and the preceding character will correct if the preceding character is a roman character. ~ Unbreakable space that stretches like a normal in- ter-word space when a line is adjusted. : Inserts a zero-width break point (similar to % but without a soft hyphen character). newline Ignored newline, for continuation lines. { Begin conditional input. } End conditional input. The special character with 2-character name st, see section __SPECIAL CHARACTERS__. [[name] The named character with arbitrary length name name. a Non-interpreted leader character. Aanything If anything is acceptable as a name of a string, macro, diversion, register, environment or font it expands to 1, and 0 otherwise. babc... Bracket building function. Banything If anything is acceptable as a valid numeric ex- pression it expands to 1, and 0 otherwise. c Interrupt text processing. Cchar The character called char; same as [[char], but compatible to other roff versions. d Forward (down) 1/2 em vertical unit (1/2 line in nroff). Dcharseq Draw a graphical element defined by the characters in charseq; see groff info file for details. e Printable version of the current escape character. E Equivalent to an escape character, but is not in- terpreted in copy-mode. fF Change to font with 1-character name or 1-digit number F. f(fo Change to font with 2-characer name or 2-digit num- ber fo. f[[font] Change to font with arbitrary length name or number expression font. g[[reg] Return format of register with name reg suitable for .af. Alternative forms g(xy and gx. hN Local horizontal motion; move right N (left if neg- ative). HN Set height of current font to N. k[[reg] Mark horizontal input place in register with arbi- trary length name reg. Alternative forms k(xy and kx. lNc Horizontal line drawing function (optionally using character c). LNc Vertical line drawing function (optionally using character c). nr The numerical value stored in the register variable with the 1-character name r. n(re The numerical value stored in the register variable with the 2-character name re. n[[reg] The numerical value stored in the register variable with arbitrary lenght name reg. Nn Typeset the character with code n in the current font, no special fonts are searched. Useful for adding characters to a font using the .char re- quest. oabc... Overstrike characters a, b, c, etc. p Break and spread output line. r Reverse 1 em vertical motion (reverse line in nroff). Rname n The same as .nr name n. s[[N] Set the point size to ''N'' scaled points. Note the alternative forms __s__''''__[[__''N''__]__, __s'__''N''__'__, __s__''''__'__''N''__'__, s(xy, __s__''''__(__''xy'', sx. Same as .ps request. SN Slant output N degrees. t Non-interpreted horizontal tab. u Reverse (up) 1/2 em vertical motion (1/2 line in nroff). vN Local vertical motion; move down N (up if nega- tive). V[[env] The contents of the environment variable env. Al- ternative forms V(xy and Vx. wstring The width of the character sequence string. xN Extra line-space function (negative before, posi- tive after). Xstring Output string as device control function. Y[[name] Output string variable or macro name uninterpreted as device control function. Alternative forms Y(xy and Yx. zc Print c with zero width (without spacing). Zanything Print anything and then restore the horizontal and vertical position; anything may not contain tabs or leaders. The escape sequences e, ., \( Escape sequences starting with or [[ do not represent single character escape sequences, but introduce escape names with two or more characters. If a backslash is followed by a character that does not constitute a defined escape sequence the backslash is silently ignored and the character maps to itself. __SPECIAL CHARACTERS__ Common special characters are predefined by escape se- quences of the form with characters x and y. Some of these exist in the usual font while most of them are only available in the special font. Below you'll find a selec- tion of the most important glyphs; a complete list can be found in groff_char(7). Bullet sign. Copyright. Cent. Double dagger. Degree. Dagger. -- Em-dash. - - Hyphen. Registered sign. Section sign. _ _ Underline character. Identical. Larger or equal. Less or equal. Not equal. Right arrow. Left arrow. Plus-minus sign. !!REGISTERS Registers are variables that store a value. In groff, most registers store numerical values (see section __NUMERI- CAL EXPRESSIONS__ above), but some can also hold a string value. Each register is given a name. Arbitrary registers can be defined and set with the request .nr register. The value stored in a register can be retrieved by the es- cape sequences introduced by n. Most useful are predefined registers. In the following the notation name is used to refer to a register called name to make clear that we speak about registers. Please keep in mind that the en[[] decoration is not part of the register name. __READ-ONLY REGISTERS__ The following registers have predefined values that should not be modified by the user (usually, registers starting with a dot a read-only). Mostly, they provide information on the current settings or store results from request calls. n[[.$] Number of arguments in the current macro. n[[.a] Post-line extra line-space most recently uti- lized using x'N'. n[[.A] Set to 1 in __troff__ if option __-A__ is used; always 1 in __nroff__. n[[.c] Current input line number. n[[.C] 1 if compatibility mode is in effect, 0 other- wise. n[[.cdp] The depth of the last character added to the current environment. It is positive if the character extends below the baseline. n[[.ce] The number of lines remaining to be centered, as set by the .ce request. n[[.cht] The height of the last character added to the current environment. It is positive if the character extends above the baseline. n[[.csk] The skew of the last character added to the cur- rent environment. The skew of a character is how far to the right of the center of a charac- ter the center of an accent over that character 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[[.fam] The current font family (string-valued). n[[.fp] The number of the next free font position. n[[.g] Always 1 in GNU troff. Macros should use it to test if running under groff. n[[.h] Text base-line high-water mark on current page or diversion. n[[.H] Available horizontal resolution in basic units. n[[.hla] The current hyphenation language as set by the __.hla__ request. n[[.hlc] The number of immediately preceding consecutive hyphenated lines. n[[.hlm] The maximum allowed number of consecutive hy- phenated lines, as set by the .hlm request. n[[.hy] The current hyphenation flags (as set by the .hy request). n[[.hym] The current hyphenation margin (as set by the .hym request). n[[.hys] The current hyphenation space (as set by the .hys request). n[[.i] Current ident. n[[.in] The indent that applies to the current output line. n[[.int] Positive if last output line contains c. n[[.kern] 1 if pairwise kerning is enabled, 0 otherwise. n[[.l] Current line length. n[[.lg] The current ligature mode (as set by the .lg re- quest). n[[.linetabs] The current line-tabs mode (as set by the .linetabs request). n[[.ll] The line length that applies to the current out- put line. n[[.lt] The title length (as set by the .lt request). n[[.n] Length of text portion on previous output line. n[[.ne] The amount of space that was needed in the last .ne request that caused a trap to be sprung. Useful in conjunction with .trunc. n[[.ns] 1 if in no-space mode, 0 otherwise. n[[.o] Current page offset. n[[.p] Current page length. n[[.pn] The number of the next page: either the value set by a .pn request, or the number of the cur- rent page plus 1. n[[.ps] The current pointsize in scaled points. n[[.psr] The last-requested pointsize in scaled points. n[[.rj] The number of lines to be right-justified as set by the rj request. n[[.s] Current point size as a decimal fraction. n[[.sr] The last requested pointsize in points as a dec- imal fraction (string-valued). n[[.t] Distance to the next trap. n[[.T] Set to 1 if option __-T__ is used. n[[.tabs] A string representation of the current tab set- tings suitable for use as an argument to the .ta request. n[[.trunc] The amount of vertical space truncated by the most recently sprung vertical position trap, or, if the trap was sprung by a .ne request, minus the amount of vertical motion produced by .ne. request. In other words, at the point a trap is sprung, it represents the difference of what the vertical position would have been but for the trap, and what the vertical position actually is. Useful in conjunction with the .ne regis- ter. n[[.ss] The value of the parameters set by the first ar- gument of the .ss request. n[[.sss] The value of the parameters set by the second argument of the .ss request. n[[.u] Equal to 1 bin fill mode and 0 in nofill mode. n[[.v] Current vertical line spacing. n[[.V] Available vertical resolution in basic units. n[[.vpt] 1 if vertical position traps are enabled, 0 oth- erwise. n[[.w] Width of previous character. n[[.warn] The sum of the number codes of the currently en- abled warnings. n[[.x] The major version number. n[[.y] The minor version number. n[[.Y] The revision number of groff. n[[.z] Name of current diversion. __WRITABLE REGISTERS__ The following registers can be read and written by the us- er. 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[[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[[mo] Current month (1-12). n[[nl] Vertical position of last printed text base-line. n[[rsb] Like sb, but takes account of the heights and depths of characters. n[[rst] Like st, but takes account of the heights and depths of characters. n[[sb] Depth of string below base line (generated by width function w). n[[skw] Right skip width from the center of the last character in the w argument. n[[slimit] If greater than 0, the maximum number of objects on the input stack. If 0 there is no limit, i.e., recursion can continue until virtual memo- ry is exhausted. n[[ssc] The amount of horizontal space (possibly nega- tive) that should be added to the last character before a subscript (generated by width function w). n[[st] Height of string above base line (generated by width function w). n[[systat] The return value of the ''system()'' function exe- cuted by the last .sy request. n[[urx] Upper right x-coordinate (in !PostScript units) of a given !PostScript image (set by .psbb). n[[ury] Upper right y-coordinate (in !PostScript units) of a given !PostScript image (set by .psbb). n[[year] The current year (year 2000 compliant). n[[yr] Current year minus 1900. For Y2K compliance use register year instead. !!WARNINGS Each warning generated by groff is identified by a name and a code number. The codes are powers of 2 to allow bit-encoding with a single integer. There are also names that can be used to refer to groups of warnings. The name associated with a warning is used by the -w and -W options; the number code is used by the .warn request and by the n[[warn] register. all group All warnings except di, mac and reg. Intended to cover all warnings with traditional macro packages. break 4 In fill mode, lines which could not be broken so that their length was less than the line length. This is enabled by default. char 1 Non-existent characters. This is enabled by default. delim 8 Missing or mismatched closing delimiters. di 256 Use of .di or .da without an argument when there is no current diversion. el 16 Use of the .el request with no matching .ie request. escape 32768 Unrecognized escape sequence. Then the escape character is ignored. font 131072 Non-existent fonts. This is enabled by de- fault. ig 262144 Illegal escapes in text ignored with the .ig request. These are conditions that are errors when they occur outside of ignored text. mac 512 Use of undefined strings, macros, and diver- sions. Automatically handled as empty. Usu- ally, only one warning per name. missing 8192 Request that is missing non-optional argu- ments. input 16384 Illegal input character. number 2 Invalid numeric expressions. This is enabled by default. range 64 Out of range arguments. reg 1024 Use of undefined number register. Automati- cally defined as having value 0. Usually, on- ly one warning per name. right-brace 4096 Use of } where a number was expected. scale 32 Meaningless scaling indicators. space 65536 Missing space between a request or macro and its argument. Then no macro is automatically defined. This is enabled by default. This warning will never occur in compatibility mode. syntax 128 Dubious syntax in numeric expressions. tab 2048 Inappropriate use of a tab character (either in an unquoted macro argument or where a num- ber was expected). w group All warnings. !!COMPATIBILITY ''groff'' provides a __compatibility mode__ that allows to process roff code written for classical or for other implementa- tions of roff in a consistent way. Compatibility mode can be turned on with the -C command line option, and turned on or off with the .cp request. The number register n(.C is 1 if compatibility mode is on, 0 otherwise. This became necessary because the GNU concept for long names causes some incompatibilities. ''Classical troff'' will interpret __.dsabcd__ as defining a string __ab__ with contents __cd__. Normally, ''groff'' will interpret this as a call of a macro named dsabcd. Also ''classical troff'' will interpret *[[ or n[[ as refer- ences to a string or number register called [[. In ''GNU na- tive mode'', however, this will normally be interpreted as the start of a long name. In ''compatibility mode'', groff will interpret these things in the traditional way, but long names are not recognized. On the other hand, groff in ''GNU native mode'' does not allow to use the escape sequences e, |, ^, ''classical troff'' does. The A escape sequence can be helpful in avoiding these escape sequences in names. Fractional pointsizes cause one noteworthy incompatibili- ty. In ''classical troff'', the .ps request ignores scale in- dicators and so __.ps 10u__ will set the pointsize to 10 points, whereas in groff na- tive mode the pointsize will be set to 10 scaled points. In ''groff'' mode, there is a fundamental difference between unformatted input characters, and formatted output charac- ters. Everything that affects how an output character will be output is stored with the character; once an out- put character has been constructed it is unaffected by any subsequent requests that are executed, including the .bd, .cs, .tkf, .tr, or .fp requests. Normally output characters are constructed from input characters at the moment immediately before the character is added to the current output line. Macros, diversions and strings are all, in fact, the same type of object; they contain lists of input characters and output charac- ters in any combination. An output character does not behave like an input charac- ter for the purposes of macro processing; it does not in- herit any of the special properties that the input charac- ter from which it was constructed might have had. The following example will make things clearer. __.di x \\ .br .di .x __ In ''GNU mode'' this will be printed as \. So each pair of input backslashes \ is turned into a single output back- slash \ and the resulting output backslashes are not in- terpreted as escape characters when they are reread. ''Classical troff'' would interpret them as escape characters when they were reread and would end up printing a single backslash . The correct way to get a printable \ is to use the e es- cape sequence. This will always print a single instance of the current escape character, regardless of whether or not it is used in a diversion. It will also work in both GNU mode and compatibility mode. To store an escape sequence in a diversion that will be interpreted when the diversion is reread, either the tra- ditional ! transparent output facility or the new ? es- cape sequence can be used. !!BUGS At the moment, the documentation of the groff system is in a state of change and evolution. It is possible that there are small inconsistencies between different docu- ments temporarily. The __WARNINGS__ section belongs to troff(1). !!AUTHOR This document is part of groff, the GNU roff distribution. It was written by Bernd Warken It is distributed under the terms of the FDL (GNU Free Documentation License) version 1.1 or later. You should have received a copy of the FDL on your system, it is also available on-line under ''http://www.gnu.org/copyleft/fdl.html''. Formerly, the extensions of the groff language were kept in the manual page troff(1). This document contains the essential parts of that documentation, but the gory de- tails are found in the groff info file. !!SEE ALSO The main source of information for the groff language is the __groff info__(1) file. For a survey of roff and the groff system and further doc- umentation pointers see roff(7). The formatter programs are described in groff(1) and troff(1); a complete of all predefined glyph names can be found in groff_char(7). The classical ''troff'' documentation is available on-line at ''http://cm.bell-labs.com/cm/cs/cstr.html'' and ''http://www.kohala.com/start/troff/''. ----
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