Name | Description | groff Elements | Control Characters | Numerical Expressions | Conditions | Requests | Escape Sequences | Registers | Hyphenation | Traps | Underlining | Compatibility | Debugging | Authors | See also | COLOPHON |
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groff(7) Miscellaneous Information Manual groff(7)
groff - GNU roff language reference
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 ‘]’. 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 behaviour can be quite tricky, but there are some rules that ensure a safe usage. 1. Printable backslashes must be denoted as \e. To be more precise, \e represents the current escape character. To get a backslash glyph, use \(rs or \[rs]. 2. Double all backslashes. 3. Begin all text lines with the non-printing input break \&. This does not produce the most efficient code, but it should work as a first measure. For better strategies, see the groff Texinfo manual and groff_tmac(5). Reading roff source files is easier, just reduce all double backslashes to a single one in all macro definitions.
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 hyphen-minus (-), 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.
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 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 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. \c at the end of an input line suppresses these functions. 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.
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 actual output device v Vertical line space in basic units 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 added the following operators for numerical expressions: e1>?e2 The maximum of e1 and e2. e1<?e2 The minimum of e1 and e2. (c;e) Evaluate e using c as the default scaling indicator. For details see the groff Texinfo manual.
Conditions are expressions tested by the .if, .ie, and the .while requests. The following table characterizes the different types of conditions. N A numerical expression N yields true if its value is greater than 0. !N True if the value of N is ≤ 0 (see below). 's1's2' True if string s1 is identical to string s2. !'s1's2' True if string s1 is not identical to string s2 (see below). c g True if a glyph g is available. d name True if there is a string, macro, diversion, or request called name. e Current page number is even. F font True if a font called font exists. m color True if there is a color called color. n Formatter is nroff. o Current page number is odd. r reg True if there is a number register called reg. S style True if a style called style has been registered. t Formatter is troff. v Always false (for compatibilty with other troff implementations). Note that the ! operator may only appear at the beginning of an expression, and negates the entire expression. This maintains bug-compatibility with AT&T troff.
This section provides a short reference for the predefined requests. In groff, request, macro, and string names can be arbitrarily long. No bracketing or marking of long names is needed. Most requests take one or more arguments. The arguments are separated by space characters (no tabs!); there is no inherent limit for their length or number. Some requests have optional arguments with a different behaviour. Not all of these details are outlined here. Refer to the groff Texinfo manual and groff_diff(7) for all details. In the following request specifications, most argument names were chosen to be descriptive. Only the following denotations need clarification. c denotes a single character. font a font either specified as a font name or a font number. anything all characters up to the end of the line or within \{ and \}. n is a numerical expression that evaluates to an integer value. N is an arbitrary numerical expression, signed or unsigned. ±N has three meanings depending on its sign, described below. If an expression defined as ±N starts with a ‘+’ sign the resulting value of the expression is added to an already existing value inherent to the related request, e.g., adding to a number register. If the expression starts with a ‘-’ the value of the expression is subtracted from the request value. Without a sign, N replaces the existing value directly. To assign a negative number either prepend 0 or enclose the negative number in parentheses. Request short reference . Empty line, ignored. Useful for structuring documents. .\" anything Complete line is a comment. .ab string Print string on standard error, exit program. .ad Enable output line adjustment. .ad c Adjust output lines 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 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 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 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 name Invoke macro name after the end of input. .eo Turn off escape character mechanism. .ev Switch to previous environment and pop it off the stack. .ev env Push down environment number or name env to the stack and switch to it. .evc env Copy the contents of environment env to the current environment. No pushing or popping. .ex Exit from roff processing. .fam Return to previous font family. .fam name Set the current font family to name. .fc Disable field mechanism. .fc a Set field delimiter to a and pad 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 Fill output lines. .fl Flush output buffer. .fp n font Mount font on position n. .fp n internal external Mount font with long external name to short internal name on position n. .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 hyphenation mode to 1 (the default). .hy 0 Disable hyphenation; same as .nh. .hy mode Set 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 anything If cond then anything, otherwise skip to .el. .if cond anything If cond then anything; otherwise do nothing. .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 (i.e., calculate tab positions relative to output line). .linetabs n If n is zero, disable line-tabs mode, otherwise enable it. .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 The same as .so except that file is searched in the tmac directories. .na Disable line adjustment. .ne Need a one-line vertical space. .ne N Need N vertical space (default scaling indicator v). .nf No filling or adjusting of output lines. .nh Disable 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 Always process anything. .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 Print the current environment and each defined environment state to stderr. .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 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 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 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 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+m×rn+r1 through nn+m×rn+rn, where m increments from 0, 1, 2, ... to infinity. .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) 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 anything While condition cond is true, accept anything as input. .write stream anything Write anything to the stream named stream. .writec stream anything Similar to .write without emitting a final newline. .writem stream xx Write contents of macro or string xx to the stream named stream. Besides these standard groff requests, there might be further macro calls. They can originate from a macro package (see roff(7) for an overview) or from a preprocessor. Preprocessor macros are easy to 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 │ none │ none │ │ 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.
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. Escape short reference \" Start of a comment. Everything up to the end of the line is ignored. \# Everything up to and including the next newline is ignored. This is interpreted in copy mode. This is like \" except that the terminating newline is ignored as well. \*s The string stored in the string variable with one- character name s. \*(st The string stored in the string variable with two- character name st. \*[string] The string stored in the string variable with name string (with arbitrary length). \*[stringvar arg1 arg2 ...] The string stored in the string variable with arbitrarily long name stringvar, taking arg1, arg2, ... as arguments. \$0 The name by which the current macro was invoked. The .als request can make a macro have more than one name. \$x Macro or string argument with one-digit number x in the range 1 to 9. \$(xy Macro or string argument with two-digit number xy (larger than zero). \$[nexp] Macro or string argument with number nexp, where nexp is a numerical expression evaluating to an integer ≥1. \$* In a macro or string, the concatenation of all the arguments separated by spaces. \$@ In a macro or string, the concatenation of all the arguments with each surrounded by double quotes, and separated by spaces. \$^ In a macro, the representation of all parameters as if they were an argument to the .ds request. \\ reduces to a single backslash; useful to delay its interpretation as escape character in copy mode. For a printable backslash, use \e, or even better \[rs], to be independent from the current escape character. \' The acute accent ´; same as \(aa. \` The grave accent `; same as \(ga. \- The - (minus) sign in the current font. \_ The same as \(ul, the underline character. \. The same as a dot (‘.’). Necessary in nested macro definitions so that ‘\\..’ expands to ‘..’. \% Default hyphenation character. \! Transparent line indicator. \?anything? In a diversion, this transparently embeds anything in the diversion. anything is read in copy mode. See also the escape sequences \! and \?. \space Unpaddable space size space glyph (no line break). \0 Digit-width unbreakable space. \| 1/6 em narrow unbreakable space glyph; zero-width in nroff. \^ 1/12 em half-narrow unbreakable space glyph; zero-width in nroff. \& Non-printing input break. \) Like \& except that it behaves like a glyph declared with the .cflags request to be transparent for the purposes of end-of-sentence recognition. \/ Increases the width of the preceding glyph so that the spacing between that glyph and the following glyph is correct if the following glyph is a roman glyph. \, Modifies the spacing of the following glyph so that the spacing between that glyph and the preceding glyph is correct if the preceding glyph is a roman glyph. \~ Unbreakable space that stretches like a normal inter-word space when a line is adjusted. \: Insert a non-printing break point (similar to \% but without a soft hyphen character). \newline Ignored newline, for continuation lines. \{ Begin conditional input. \} End conditional input. \(sc A glyph with two-character name sc; see section “Special Characters” below. \[name] A glyph with name name (of arbitrary length). \[comp1 comp2 ...] A composite glyph with components comp1, comp2, ... \a Non-interpreted leader character. \A'anything' If anything is acceptable as a name of a string, macro, diversion, register, environment or font it expands to 1, and to 0 otherwise. \b'abc...' Bracket building function. \B'anything' If anything is acceptable as a valid numeric expression it expands to 1, and to 0 otherwise. \c Continue output line at next input line. Anything after this escape on the same line is ignored except \R (which works as usual). Anything before \c on the same line is appended to the current partial output line. The next non-command line after a line interrupted with \c counts as a new input line. \C'glyph' The glyph called glyph; same as \[glyph], but compatible to other roff versions. \d Forward (down) 1/2 em (1/2 line in nroff). \D'charseq' Draw a graphical element defined by the characters in charseq; see the groff Texinfo manual for details. \e Printable version of the current escape character. \E Equivalent to an escape character, but is not interpreted in copy mode. \fF Change to font with one-character name or one-digit number F. \fP Switch back to previous font. \f(fo Change to font with two-character name or two-digit number fo. \f[font] Change to font with arbitrarily long name or number expression font. \f[] Switch back to previous font. \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 back to previous font family. \gr Return format of register with one-character name r suitable for .af request. \g(rg Return format of register with two-character name rg suitable for .af request. \g[reg] Return format of register with arbitrarily long name reg suitable for .af request. \h'N' Local horizontal motion; move right N (left if negative). \H'N' Set height of current font to N. \kr Mark horizontal position in one-character register r. \k(rg Mark horizontal position in two-character register rg. \k[reg] Mark horizontal position in register with arbitrarily long name reg. \l'Nc' Horizontal line drawing function (optionally using character c). \L'Nc' Vertical line drawing function (optionally using character c). \mc Change to color with one-character name c. \m(cl Change to color with two-character name cl. \m[color] Change to color with arbitrarily long name color. \m[] Switch back to previous color. \Mc Change filling color for closed drawn objects to color with one-character name c. \M(cl Change filling color for closed drawn objects to color with two-character name cl. \M[color] Change filling color for closed drawn objects to color with arbitrarily long name color. \M[] Switch to previous fill color. \nr The numerical value stored in the register variable with the one-character name r. \n(re The numerical value stored in the register variable with the two-character name re. \n[reg] The numerical value stored in the register variable with arbitrarily long name reg. \N'n' Typeset the glyph with index n in the current font. No special fonts are searched. Useful for adding (named) entities to a document using the .char request and friends. \o'abc...' Overstrike glyphs a, b, c, etc. \O0 Disable glyph output. Mainly for internal use. \O1 Enable glyph output. Mainly for internal use. \p Break output line at next word boundary; adjust if applicable. \r Reverse 1 em vertical motion (reverse line in nroff). \R'name ±n' The same as .nr name ±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, same 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. Same as .ps request. \s[±N] \s±[N] \s'±N' \s±'N' Set/increase/decrease the point size to/by N scaled points. Same as .ps request. \S'N' Slant output by N degrees. \t Non-interpreted horizontal tab. \u Reverse (up) 1/2 em vertical motion (1/2 line in nroff). \v'N' Local vertical motion; move down N (up if negative). \Ve The contents of the environment variable with one- character name e. \V(ev The contents of the environment variable with two- character name ev. \V[env] The contents of the environment variable with arbitrarily long name env. \w'string' The width of the glyph sequence string. \x'N' Extra line-space function (negative before, positive after). \X'string' Output string as device control function. \Yn Output string variable or macro with one-character name n uninterpreted as device control function. \Y(nm Output string variable or macro with two-character name nm uninterpreted as device control function. \Y[name] Output string variable or macro with arbitrarily long name name uninterpreted as device control function. \zc Print c with zero width (without spacing). \Z'anything' Print anything and then restore the horizontal and vertical position; anything may not contain tabs or leaders. The escape sequences \e, \., \", \$, \*, \a, \n, \t, \g, and \newline are interpreted in copy mode. Escape sequences starting with \( or \[ do not represent single character escape sequences, but introduce escape names with two or more characters. If a backslash is followed by a character that does not constitute a defined escape sequence, the backslash is silently ignored and the character maps to itself. Identifiers An identifier is a label for an object of syntactical importance like a register, a name (macro, string, diversion, or box), 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, 0x0D–0x1F, and 0x80–0x9F. On an EBCDIC host, they are 0x00–0x01, 0x08, 0x09, 0x0B, 0x0D–0x14, 0x17–0x1F, and 0x30–0x3F. 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 0x80–0x9F 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”. Special characters [Note: ‘Special Characters’ is a misnomer; those entities are (output) glyphs, not (input) characters.] Common special characters are predefined by escape sequences of the form \(xy with characters x and y. In groff, it is also possible to use the form \[xy]. Some of these special characters exist in the usual font while most of them are only available in the special font. Below you can see a small selection of the most important glyphs; a complete list can be found in groff_char(7). \(Do Dollar $ \(Eu Euro € \(Po British pound sterling £ \(aq Apostrophe quote ' \(bu Bullet sign • \(co Copyright © \(cq Single closing quote (right) ’ \(ct Cent ¢ \(dd Double dagger ‡ \(de Degree sign ° \(dg Dagger † \(dq Double quote " \(em Em-dash — \(en En-dash – \(ha Caret/spacing circumflex accent (“hat”) ^ \(hy Hyphen ‐ \(lq Double quote left “ \(oq Single opening quote (left) ‘ \(rg Registered sign ® \(rq Double quote right ” \(rs Reverse solidus/backslash \ \(sc Section sign § \(ti Tilde (spacing) ~ \(tm Trademark symbol ™ \(ul Underline character _ \(== Identical ≡ \(>= Larger or equal ≥ \(<= Less or equal ≤ \(!= Not equal ≠ \(-> Right arrow → \(<- Left arrow ← \(+- Plus-minus sign ± Unicode characters The extended escape u allows the inclusion of all available Unicode characters into a roff file. \[uxxxx] u is the escape name. xxxx is a hexadecimal number of four hex digits, such as 0041 for the letter A, thus \[u0041]. \[uyyyyy] u is the escape name. yyyyy is a hexadecimal number of five hex digits, such as 2FA1A for a Chinese-looking character from the Unicode block CJK Compatibility Ideographs Supplement, thus \[u2FA1A]. The hexadecimal value indicates the corresponding Unicode code point for a character. \[uhex1_hex2] \[uhex1_hex2_hex3] hex1, hex2, and hex3 are all Unicode hexadecimal codes (4 or 5 hex digits) that are used for overstriking, e.g., \[u0041_0301] is A acute, which can also be specified as Á; see groff_char(7). The availability of the Unicode characters depends on the font used. For text mode, the device -Tutf8 is quite complete; for troff modes it might happen that some or many characters will not be displayed. Please check your fonts. Strings 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 (and boxes) share the same 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 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. 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] 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 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] The current adjustment mode. It can be stored and used to set adjustment. (n = 1, b = 1, l = 0, r = 5, c = 3). \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 in fill mode and 0 in no-fill mode. \n[.U] Equal to 1 in safer mode and 0 in unsafe mode. \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. \n[.y] The minor version number. \n[.Y] The revision number of groff. \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] Vertical position of last printed text base-line. \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 (year 2000 compliant). \n[yr] Current year minus 1900. For Y2K compliance use register year instead.
Several requests influence hyphenation. Because conventions vary, a variety of hyphenation modes are available to the .hy request; these determine whether automatic 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 hyphenation is permissible. The default is “1” for historical reasons, but this is not an appropriate value for the U.S. English hyphenation patterns used by groff, 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, this value prevents hyphenation if the next page position trap is closer than the next line of text would be. groff automatically inserts an implicit page position trap at the end of each page to cause a page transition. This value can be used in traps planted by users or macro packages 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. Note that any 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). See groff_diff(7) or the groff Texinfo manual for further details.
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 invoked 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]).
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
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).
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 identity of the 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, diversions, and boxes (.pm); environments (.pev), registers (.pnr), and page location traps (.ptr) to the standard error stream.
This document was written by Bernd Warken ⟨groff-bernd.warken-72@ web.de⟩.
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 format, and 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.
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