groff (7)

NAME

groff - a short reference for the GNU roff language

DESCRIPTION

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

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

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

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

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

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

Control lines represent commands, optionally with arguments. They have the following syntax. The leading control character can be followed by a command name; arguments, if any, are separated by spaces (but not tab characters) from the command name and among themselves, for example,

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 special non-spacing character \&.

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

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

GROFF ELEMENTS

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

There are two kinds of roff commands, possibly with arguments. Requests are written on a line of their own starting with a dot or a whereas Escape sequences are in-line functions and in-word formatting elements starting with a backslash

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

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

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

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

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

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

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

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

CONTROL CHARACTERS

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

.: A dot is only special at the beginning of a line or after the condition in the requests if , ie , el , and while . There it is the control character that introduces a request (or macro). 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 do work). In all other positions, it denotes the single quote or apostrophe character. Groff provides a printable representation with the \(cq escape sequence.
": The double quote is used to enclose arguments in macros (but not in requests and strings). In the ds and as requests, a leading double quote in the argument is stripped off, making everything else afterwards the string to be defined (enabling leading whitespace). The escaped double quote \" introduces a comment. Otherwise, it is not special. Groff provides a printable representation with the \(dq escape sequence.
\: The backslash usually introduces an escape sequence (this can be changed with the ec request). A printed version of the escape character is the \e escape; a backslash glyph can be obtained by \(rs.
(: The open parenthesis is only special in escape sequences when introducing an escape name or argument consisting of exactly two characters. In groff, this 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 are only functional characters. They separate the arguments in requests, macros, and strings, and the words in text lines. They are subject to groff's horizontal spacing calculations. To get a defined space width, escape sequences like (this is the escape character followed by a space), \|, \^, or \h should be used.
newline: In text paragraphs, newlines mostly behave like space characters. Continuation lines can be specified by an escaped newline, i.e., by specifying a backslash as the last character of a line.
tab: If a tab character occurs during text the interpreter makes a horizontal jump to the next pre-defined tab position. There is a sophisticated interface for handling tab positions.

NUMERICAL EXPRESSIONS

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

The roff language defines the following scaling indicators.

c: Centimeter
i: Inch
P: Pica = 1/6 inch
p: Point = 1/72 inch
m: Em = the font size in points (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 scaled point = 1/sizescale of a point (defined in font DESC file)
f: Scale by 65536.

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

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

Moreover, groff added the following operators for numerical expressions:

e1/>?,e2: The maximum of e1 and e2.
e1/<?,e2: The minimum of e1 and e2.
(,c/;,e/): Evaluate e using c as the default scaling indicator.

For details see the groff info file.

CONDITIONS

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

N: A numerical expression N yields true if its value is greater than~0.
!N: True if the value of 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).
cch: True if there is a glyph~ch available.
dname: True if there is a string, macro, diversion, or request called name.
e: Current page number is even.
o: Current page number is odd.
mname: True if there is a color called name.
n: Formatter is nroff.
rreg: True if there is a register named reg.
t: Formatter is troff.
Ffont: True if there exists a font named font.
Sstyle: True if a style named style has been registered.

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.

REQUESTS

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 info file and groff_diff(7) for all details.

In the following request specifications, most argument names were chosen to be descriptive. Only the following denotations need clarification.

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

If an expression defined as ±N starts with a sign the resulting value of the expression 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.
: Complete line is a comment.
: Print string on standard error, exit program.
: Begin line adjustment for output lines in current adjust mode.
: Start line adjustment in mode c (c/=l,r,c,b,n).
: Assign format c to register (c/=l,i,I,a,A).
: Create alias name for register.
: Create alias name for request, string, macro, or diversion object.
: Append to macro until .. is encountered.
: Append to macro until .end is called.
: Same as .am but with compatibility mode switched off during macro expansion.
: Same as .am but with compatibility mode switched off during macro expansion.
: Append to a macro whose name is contained in the string register macro until .. is encountered.
: Append to a macro indirectly. macro and end are string registers whose contents are interpolated for the macro name and the end macro, respectively.
: Same as .ami but with compatibility mode switched off during macro expansion.
: Same as .ami but with compatibility mode switched off during macro expansion.
: Append anything to stringvar.
: Same as .as but with compatibility mode switched off during string expansion.
: Unformat ASCII characters, spaces, and some escape sequences in diversion.
: Print a backtrace of the input on stderr.
: Embolden font by N\-1 units.
: Embolden Special Font S when current font is font.
: Unset the blank line macro.
: Set the blank line macro to macro.
: End current diversion.
: Divert to macro, omitting a partially filled line.
: End current diversion.
: Divert and append to macro, omitting a partially filled line.
: Eject current page and begin new page.
: Eject current page; next page number ±N.
: Line break.
: Break and spread output line. Same as \p.
: Break out of a while loop.
: Reset no-break control character to
: Set no-break control character to c.
: Reset control character to
: Set control character to c.
: Center the next input line.
: Center following N input lines.
: Copy contents of file filename unprocessed to stdout or to the diversion.
: Treat characters c1, c2, ... according to mode number.
: Change trap location to N.
: Define entity c as string anything.
: Chop the last character off macro, string, or diversion object.
: Assign a set of characters, character ranges, or classes c1, c2, ... to name.
: Close the stream.
: Enable colors.
: If N is zero disable colors, otherwise enable them.
: Map glyph name from to glyph name to while constructing a composite glyph name.
: Finish the current iteration of a while loop.
: Enable compatibility mode.
: If N is zero disable compatibility mode, otherwise enable it.
: Set constant character width mode for font to N/36 ems with em M.
: Continuous underline in nroff, like .ul in troff.
: End current diversion.
: Divert and append to macro.
: Define or redefine macro until .. is encountered.
: Define or redefine macro until .end is called.
: Same as .de but with compatibility mode switched off during macro expansion.
: Same as .de but with compatibility mode switched off during macro expansion.
: 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~ 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.
: Define or redefine a macro whose name is contained in the string register macro until .. is encountered.
: 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.
: Same as .dei but with compatibility mode switched off during macro expansion.
: Same as .dei but with compatibility mode switched off during macro expansion.
: Write anything to the intermediate output as a device control function.
: Write contents of macro or string name uninterpreted to the intermediate output as a device control function.
: End current diversion.
: Divert to macro.
: Interpret .name with compatibility mode disabled.
: Set stringvar to anything.
: Same as .ds but with compatibility mode switched off during string expansion.
: Set diversion trap to position N (default scaling indicator~
: Reset escape character to
: Set escape character to c.
: Restore escape character saved with .ecs .
: Save current escape character.
: Else part for if-else ( ie ) request.
: The macro is run after the end of input.
: Turn off escape character mechanism.
: Switch to previous environment and pop it off the stack.
: Push down environment number or name env to the stack and switch to it.
: Copy the contents of environment env to the current environment. No pushing or popping.
: Exit from roff processing.
: Return to previous font family.
: Set the current font family to name.
: Disable field mechanism.
: Set field delimiter to~a and pad glyph to space.
: Set field delimiter to~a and pad glyph to~b.
: Define fallback character (or glyph) c as string anything.
: Set fill color to previous fill color.
: Set fill color to c.
: Fill output lines.
: Flush output buffer.
: Mount font on position n.
: Mount font with long external name to short internal name on position n.
: Define fallback character (or glyph) c for font f as string anything.
: Reset list of special fonts for font to be empty.
: When the current font is font, then the fonts s1, s2, ... are special.
: Return to previous font. Same as \f[] or \fP .
: Change to font name or number font; same as escape sequence.
: Translate font1 to font2.
: Don't magnify font.
: Set zoom factor for font (in multiples of 1/1000th).
: Set glyph color to previous glyph color.
: Set glyph color to c.
: Remove additional hyphenation indicator character.
: Set up additional hyphenation indicator character~c.
: Set the hyphenation code of character c1 to code1, that of c2 to code2, etc.
: Set the current hyphenation language to lang.
: Set the maximum number of consecutive hyphenated lines to n.
: Read hyphenation patterns from file.
: Append hyphenation patterns from file.
: Set input mapping for .hpf .
: List of words with exceptional hyphenation.
: Switch to hyphenation mode N.
: Set the hyphenation margin to n (default scaling indicator~
: Set the hyphenation space to n.
: If cond then anything else goto .el .
: If cond then anything; otherwise do nothing.
: Ignore text until .. is encountered.
: Ignore text until .end is called.
: Change to previous indentation value.
: Change indentation according to ±N (default scaling indicator~
: Set an input-line count trap for the next N lines.
: Same as .it but count lines interrupted with \c as one line.
: Enable pairwise kerning.
: If n is zero, disable pairwise kerning, otherwise enable it.
: Remove leader repetition glyph.
: Set leader repetition glyph to~c.
: Write the length of the string anything to register.
: Enable line-tabs mode (i.e., calculate tab positions relative to output line).
: If n is zero, disable line-tabs mode, otherwise enable it.
: Set input line number to N.
: Set input line number to N and filename to file.
: Ligature mode on if N>0.
: Change to previous line length.
: Set line length according to ±N (default length default scaling indicator~
: Unset the leading spaces macro.
: Set the leading spaces macro to macro.
: Change to the previous value of additional intra-line skip.
: Set additional intra-line skip value to N, i.e., N\-1 blank lines are inserted after each text output line.
: Length of title (default scaling indicator~
: Margin glyph off.
: Print glyph~c after each text line at actual distance from right margin.
: Set margin glyph to~c and distance to~N from right margin (default scaling indicator~
: Mark current vertical position in register.
: The same as .so except that file is searched in the tmac directories.
: No output-line adjusting.
: Need a one-line vertical space.
: Need N vertical space (default scaling indicator~
: No filling or adjusting of output-lines.
: No hyphenation.
: Number mode off.
: In line number mode, set number, multiple, spacing, and indentation.
: Do not number next line.
: Do not number next N lines.
: Always process anything.
: Define or modify register using ±N with auto-increment M.
: Make the built-in conditions n true and t false.
: Turn on no-space mode.
: Immediately jump to end of current file.
: Immediately continue processing with file file.
: Open filename for writing and associate the stream named stream with it.
: Like .open but append to it.
: Output vertical distance that was saved by the sv request.
: Emit string directly to intermediate output, allowing leading whitespace if string starts with " (which is stripped off).
: Reset page number character to~
: Page number character.
: Print the current environment and each defined environment state to stderr.
: Pipe output to program (nroff only).
: Set page length to default The current page length is stored in .p .
: Change page length to ±N (default scaling indicator~
: Print macro names and sizes (number of blocks of 128 bytes).
: Print only total of sizes of macros (number of 128 bytes blocks).
: Next page number N.
: Print the names and contents of all currently defined number registers on stderr.
: Change to previous page offset. The current page offset is available in .o .
: Page offset N.
: Return to previous point size.
: Point size; same as
: Get the bounding box of a PostScript image filename.
: This behaves like the so request except that input comes from the standard output of command.
: Print the names and positions of all traps (not including input line traps and diversion traps) on stderr.
: Change to previous post-vertical line spacing.
: Change post-vertical line spacing according to ±N (default scaling indicator~
: Remove the definitions of entities c1, c2, ...
: Read insertion.
: Return from a macro.
: Return twice, namely from the macro at the current level and from the macro one level higher.
: Remove the definitions of entities c1, c2, ... for font f.
: Right justify the next n input lines.
: Remove request, macro, or string name.
: Rename request, macro, or string old to new.
: Rename register reg1 to reg2.
: Remove register.
: Restore spacing; turn no-space mode off.
: Return (upward only) to marked vertical place (default scaling indicator~
: Define global fallback character (or glyph)~c as string anything.
: Reset soft hyphen glyph to \(hy.
: Set the soft hyphen glyph to~c.
: In a macro, shift the arguments by n~positions.
: Set available font sizes similar to the sizes command in a DESC file.
: Include source file.
: Skip one line vertically.
: Space vertical distance N up or down according to sign of N (default scaling indicator~
: Reset global list of special fonts to be empty.
: Fonts s1, s2, etc. are special and are searched for glyphs not in the current font.
: Toggle the spread warning on and off without changing its value.
: Emit a warning if each space in an output line is widened by limit or more (default scaling indicator~
: Set space glyph size to N/12 of the space width in the current font.
: Set space glyph size to N/12 and sentence space size set to M/12 of the space width in the current font.
: Associate style with font position n.
: Replace the string named xx with the substring defined by the indices n1 and n2.
: Save of vertical space.
: Save the vertical distance N for later output with os request (default scaling indicator~
: Execute program command-line.
: Set tabs after every position that is a multiple of N (default scaling indicator~
: 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.
: Remove tab repetition glyph.
: Set tab repetition glyph to~c.
: Temporary indent next line (default scaling indicator~
: Enable track kerning for font.
: Three-part title.
: Print anything on stdout.
: Print anything on stdout, allowing leading whitespace if anything starts with " (which is stripped off).
: Similar to .tm1 without emitting a final newline.
: Translate a to b, c to d, etc. on output.
: Transparently output the contents of file filename.
: This is the same as the tr request except that the asciify request uses the character code (if any) before the character translation.
: 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 \!.
: Make the built-in conditions t true and n false.
: Set underline font to font (to be switched to by .ul ).
: Underline (italicize in troff) N input lines.
: Unformat space characters and tabs in diversion, preserving font information.
: Enable vertical position traps if n is non-zero, disable them otherwise.
: Change to previous vertical base line spacing.
: Set vertical base line spacing to ±N (default scaling indicator~
: Set warnings code to n.
: Set scaling indicator used in warnings to si.
: Remove (first) trap at position N.
: Set location trap; negative means from page bottom.
: While condition cond is true, accept anything as input.
: Write anything to the stream named stream.
: Similar to .write without emitting a final newline.
: Write contents of macro or string xx to the stream named stream.

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

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

preprocessor	start macro	end macro

eqn	.EQ	.EN
grap	.G1	.G2
grn	.GS	.GE
pic	.PS	.PE
refer	.R1	.R2
soelim	none	none
tbl	.TS	.TE

ESCAPE SEQUENCES

Escape sequences are in-line language elements usually introduced by a backslash and followed by an escape name and sometimes by a required argument. Input processing is continued directly after the escaped character or the argument (without an intervening separation character). So there must be a way to determine the end of the escape name and the end of the argument.

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

There are abbreviations for short names. Two-character escape names can be specified by an opening parenthesis like \(xy or \*(xy without a closing counterpart. And all one-character names different from the special characters and can even be specified without a marker, for example \nc or \$c.

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

While one-character escape sequences are mainly used for in-line functions and system related tasks, the two-letter names following the \( construct are glyphs predefined by the roff system; these are called `Special Characters' in the classical documentation. Escapes sequences of the form denote glyphs too.

Single-Character Escapes

: 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.
: The string stored in the string variable with one-character name~s.
: The string stored in the string variable with two-character name st.
: The string stored in the string variable with name string (with arbitrary length).
: The string stored in the string variable with arbitrarily long name stringvar, taking arg1, arg2, ... as arguments.
: The name by which the current macro was invoked. The als request can make a macro have more than one name.
: Macro or string argument with one-digit number~x in the range 1 to~9.
: Macro or string argument with two-digit number xy (larger than zero).
: 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. Unescaped: apostrophe, right quotation mark, single quote (ASCII 0x27).
: The grave accent `; same as \(ga. Unescaped: left quote, backquote (ASCII 0x60).
: 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 optional hyphenation character.
: Transparent line indicator.
: In a diversion, this transparently embeds anything in the diversion. anything is read in copy mode. See also the escape sequences \! and \?.
: Unpaddable space size space glyph (no line break).
: Digit-width space.
: 1/6 em narrow space glyph; zero width in nroff.
: 1/12 em half-narrow space glyph; zero width in nroff.
: Non-printable, zero-width glyph.
: 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.
: Inserts a zero-width break point (similar to \% but without a soft hyphen character).
: Ignored newline, for continuation lines.
: Begin conditional input.
: End conditional input.
: A glyph with two-character name sc; see section Special Characters.
: A glyph with name name (of arbitrary length).
: A composite glyph with components comp1, comp2, ...
: Non-interpreted leader character.
: If anything is acceptable as a name of a string, macro, diversion, register, environment or font it expands to~1, and to~0 otherwise.
: Bracket building function.
: If anything is acceptable as a valid numeric expression it expands to~1, and to~0 otherwise.
: Interrupt text processing.
: The glyph called glyph; same as but compatible to other roff versions.
: Forward (down) 1/2 em (1/2 line in nroff).
: Draw a graphical element defined by the characters in charseq; see the groff info file for details.
: Printable version of the current escape character.
: Equivalent to an escape character, but is not interpreted in copy mode.
: Change to font with one-character name or one-digit number~F.
: Switch back to previous font.
: Change to font with two-character name or two-digit number fo.
: Change to font with arbitrarily long name or number expression font.
: Switch back to previous font.
: Change to font family with one-character name~f.
: Change to font family with two-character name fm.
: Change to font family with arbitrarily long name fam.
: Switch back to previous font family.
: Return format of register with one-character name~r suitable for af request.
: Return format of register with two-character name rg suitable for af request.
: Return format of register with arbitrarily long name reg suitable for af request.
: Local horizontal motion; move right N (left if negative).
: Set height of current font to N.
: Mark horizontal input place in one-character register~r.
: Mark horizontal input place in two-character register rg.
: Mark horizontal input place in register with arbitrarily long name reg.
: Horizontal line drawing function (optionally using character c).
: Vertical line drawing function (optionally using character c).
: Change to color with one-character name~c.
: Change to color with two-character name cl.
: Change to color with arbitrarily long name color.
: Switch back to previous color.
: Change filling color for closed drawn objects to color with one-character name~c.
: Change filling color for closed drawn objects to color with two-character name cl.
: Change filling color for closed drawn objects to color with arbitrarily long name color.
: Switch to previous fill color.
: The numerical value stored in the register variable with the one-character name~r.
: The numerical value stored in the register variable with the two-character name re.
: The numerical value stored in the register variable with arbitrarily long name reg.
: 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.
: Overstrike glyphs a, b, c, etc.
: Disable glyph output. Mainly for internal use.
: Enable glyph output. Mainly for internal use.
: Break and spread output line.
: Reverse 1 em vertical motion (reverse line in nroff).
: The same as .nr name ±n.
: Set/increase/decrease the point size to/by N scaled points; N is a one-digit number in the range 1 to~9. Same as ps request.
: Set/increase/decrease the point size to/by N scaled points; N is a two-digit number ≥1. Same as ps request.
: Set/increase/decrease the point size to/by N scaled points. Same as ps request.
: Slant output by N degrees.
: Non-interpreted horizontal tab.
: Reverse (up) 1/2 em vertical motion (1/2 line in nroff).
: Local vertical motion; move down N (up if negative).
: The contents of the environment variable with one-character name~e.
: The contents of the environment variable with two-character name ev.
: The contents of the environment variable with arbitrarily long name env.
: The width of the glyph sequence string.
: Extra line-space function (negative before, positive after).
: Output string as device control function.
: Output string variable or macro with one-character name~n uninterpreted as device control function.
: Output string variable or macro with two-character name nm uninterpreted as device control function.
: Output string variable or macro with arbitrarily long name name uninterpreted as device control function.
: Print c with zero width (without spacing).
: 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 are interpreted in copy mode.

Escape sequences starting with \( or \[ do not represent single character escape sequences, but introduce escape names with two or more characters.

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

Special Characters

[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. Some of these exist in the usual font while most of them are only available in the special font. Below you can find a selection of the most important glyphs; a complete list can be found in groff_char(7).

: Bullet sign
: Copyright
: Cent
: Double dagger
: Degree
: Dagger
: Printable double quote
: Em-dash
: Hyphen
: Registered sign
: Printable backslash character
: Section sign
: Underline character
: Identical
: Larger or equal
: Less or equal
: Not equal
: Right arrow
: Left arrow
: Plus-minus sign

Strings

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

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

: The name of the current output device as specified by the command line option.

REGISTERS

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

Each register is given a name. Arbitrary registers can be defined and set with the 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 name to make clear that we speak about registers. Please keep in mind that the 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.

: The process ID of troff.
: Number of arguments in the current macro or string.
: Post-line extra line-space most recently utilized using \x.
: Set to~1 in troff if option is used; always~1 in nroff.
: The emboldening offset while .bd is active.
: Within a macro, set to~1 if macro called with the `normal' control character, and to~0 otherwise.
: Current input line number.
: 1~if compatibility mode is in effect, 0~otherwise.
: The depth of the last glyph added to the current environment. It is positive if the glyph extends below the baseline.
: The number of lines remaining to be centered, as set by the ce request.
: The height of the last glyph added to the current environment. It is positive if the glyph extends above the baseline.
: 1~if colors are enabled, 0~otherwise.
: 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.
: Current vertical place in current diversion; equal to nl .
: The name or number of the current environment (string-valued).
: Current font number.
: The name of the current input file (string-valued).
: The current font family (string-valued).
: The current (internal) real font name (string-valued).
: The number of the next free font position.
: Always 1 in GNU troff. Macros should use it to test if running under groff.
: Text base-line high-water mark on current page or diversion.
: Available horizontal resolution in basic units.
: The current font height as set with \H .
: The current hyphenation language as set by the hla request.
: The number of immediately preceding consecutive hyphenated lines.
: The maximum allowed number of consecutive hyphenated lines, as set by the hlm request.
: The current hyphenation flags (as set by the hy request).
: The current hyphenation margin (as set by the hym request).
: The current hyphenation space (as set by the hys request).
: Current indentation.
: The indentation that applies to the current output line.
: Positive if last output line contains \c.
: The current adjustment mode. It can be stored and used to set adjustment. (n = 1, b = 1, l = 0, r = 5, c = 3).
: The current horizontal output position (relative to the current indentation).
: 1~if pairwise kerning is enabled, 0~otherwise.
: Current line length.
: The current line spacing setting as set by .ls .
: The current ligature mode (as set by the lg request).
: The current line-tabs mode (as set by the linetabs request).
: The line length that applies to the current output line.
: The title length (as set by the lt request).
: The current drawing color (string-valued).
: The current background color (string-valued).
: Length of text portion on previous output line.
: The amount of space that was needed in the last ne request that caused a trap to be sprung. Useful in conjunction with .trunc .
: 1~if in no-space mode, 0~otherwise.
: Current page offset.
: The suppression nesting level (see \O).
: Current page length.
: 1~if the current page is being printed, 0~otherwise (as determined by the command line option).
: 1~during page ejection, 0~otherwise.
: The number of the next page: either the value set by a pn request, or the number of the current page plus 1.
: The current point size in scaled points.
: The last-requested point size in scaled points.
: The current post-vertical line spacing.
: The number of unused number registers. Always 10000 in GNU troff.
: The number of lines to be right-justified as set by the rj request.
: Current point size as a decimal fraction.
: The slant of the current font as set with \S .
: The last requested point size in points as a decimal fraction (string-valued).
: The value of the parameters set by the first argument of the ss request.
: The value of the parameters set by the second argument of the ss request.
: The current font style (string-valued).
: Vertical distance to the next trap.
: Set to~1 if option is used.
: A string representation of the current tab settings suitable for use as an argument to the ta request.
: 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 . Useful in conjunction with the .ne .
: Equal to 1 in fill mode and 0 in no-fill mode.
: Equal to 1 in safer mode and 0 in unsafe mode.
: Current vertical line spacing.
: Available vertical resolution in basic units.
: 1~if vertical position traps are enabled, 0~otherwise.
: Width of previous glyph.
: The sum of the number codes of the currently enabled warnings.
: The major version number.
: The minor version number.
: The revision number of groff.
: Name of current diversion.
: 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.

: Current page number.
Current input line number.
Character type (set by width function \w).
Maximal width of last completed diversion.
Height of last completed diversion.
Current day of week (1-7).
Current day of month (1-31).
The number of hours past midnight. Initialized at start-up.
Current horizontal position at input line.
Lower left x-coordinate (in PostScript units) of a given PostScript image (set by .psbb ).
Lower left y-coordinate (in PostScript units) of a given PostScript image (set by .psbb ).
Output line number.
The number of leading spaces of an input line.
The horizontal space corresponding to the leading spaces of an input line.
The number of minutes after the hour. Initialized at start-up.
Current month (1-12).
Vertical position of last printed text base-line.



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 or
Like sb , but takes account of the heights and depths of glyphs.
Like st , but takes account of the heights and depths of glyphs.
Depth of string below base line (generated by width function \w).
The number of seconds after the minute. Initialized at start-up.
Right skip width from the center of the last glyph in the \w argument.
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.
The amount of horizontal space (possibly negative) that should be added to the last glyph before a subscript (generated by width function \w).
Height of string above base line (generated by width function \w).
The return value of the system() function executed by the last sy request.
Upper right x-coordinate (in PostScript units) of a given PostScript image (set by .psbb ).
Upper right y-coordinate (in PostScript units) of a given PostScript image (set by .psbb ).
The current year (year 2000 compliant).
Current year minus 1900. For Y2K compliance use year instead.

COMPATIBILITY

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

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

BUGS

Report bugs to the groff bug mailing list Include a complete, self-contained example that will allow the bug to be reproduced, and say which version of groff you are using.

AUTHORS

This document is distributed under the terms of the FDL (GNU Free Documentation License) version 1.3 or later. You should have received a copy of the FDL on your system, it is also available on-line at the GNU copyleft site

This document is part of groff, the GNU roff distribution. It was written by Bernd Warken it is maintained by Werner Lemberg