groff(7) Miscellaneous Information Manual groff(7)
Name
groff - GNU roff language reference
Description
groff is short for GNU roff, a free reimplementation of the AT&T
device-independent troff typesetting system. See roff(7) for a survey
of and background on roff systems.
This document is intended as a reference. The primary groff manual,
Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner
Lemberg, is a better resource for learners, containing many examples
and much discussion. It is written in Texinfo; you can browse it
interactively with "info groff". Additional formats, including plain
text, HTML, TeX DVI, and PDF, may be available in /opt/local/share/doc/
groff-1.24.1.
We apply the term "groff" to the language documented here, the GNU
implementation of the overall system, the project that develops that
system, and the command of that name. In the first sense, groff is an
extended dialect of the roff language, for which many similar
implementations exist.
GNU troff, installed on this system as troff(1), is the formatter: a
program that reads device and font descriptions (groff_font(5)),
interprets the groff language expressed in input text, and translates
it into a device-independent page description language (groff_out(5))
that is usually then post-processed by an output driver to produce
PostScript, PDF, HTML, DVI, or terminal output. We speak of "the
formatter" when describing behavior that is generally true of troff and
nroff programs.
Input format
Organize input to GNU troff into lines separated by the Unix newline
character (U+000A), using the character encoding it recognizes:
ISO Latin-1 (8859-1). We recommend use of ISO 646:1991 IRV (US-ASCII)
or (equivalently) the Basic Latin subset of ISO 10646 (Unicode); see
groff_char(7).
Some control characters (from the sets "C0 Controls" and "C1 Controls"
as Unicode describes them) are invalid as input characters. GNU troff
discards them upon reading. (It also emits a warning in category
"input"; see section "Warnings" of troff(1).) It processes a character
sequence "foo", followed by an invalid character and then "bar", as
"foobar".
Invalid input characters comprise 0x00, 0x0B, 0x0D-0x1F, and 0x80-0x9F.
(Historically, control characters like ASCII STX, ETX, and BEL
(Control+B, Control+C, and Control+G) respectively) have been observed
in roff documents, particularly in macro packages employing them as
delimiters with the output comparison operator to try to avoid
collisions with the content of arbitrary user-supplied parameters (see
subsection "Conditional expressions" below). We discourage this
expedient; in GNU troff it is unnecessary (outside of compatibility
mode) because the program parses delimited arguments at a different
input level than their surrounding context. See section
"Miscellaneous" of groff_diff(7).) GNU troff uses some of these code
points for internal purposes, making non-trivial the extension of the
program to accept UTF-8 or other encodings that use characters from
these ranges.
Syntax characters
Several input characters are syntactically significant to groff. The
most important of these distinguish control lines, which instruct the
formatter, from text lines that are formatted as output.
. A dot at the beginning of an input line marks it as a control line.
It can also follow the el and nop requests, and the condition in
"if", ie, and "while" requests. The control character invokes
requests and calls macros by the name that follows it. The cc
request can change the control character.
' The neutral apostrophe is the no-break control character,
recognized where the control character is. It suppresses the
(first) break implied by the bp, ce, cf, fi, fl, "in", nf, rj, sp,
ti, and trf requests. The requested operation takes effect at the
next break. It makes br and brp nilpotent. The no-break control
character can be changed with the c2 request. When formatted, "'"
may be typeset as a typographical quotation mark; use the \[aq]
special character escape sequence to format a neutral apostrophe
glyph.
" The neutral double quote can be used to enclose arguments to macros
and strings, and is required if those arguments contain space or
tab characters. The requests "as", as1, cf, char, ds, ds1, fchar,
fschar, mso, msoquiet, nx, "open", opena, pi, schar, "so", soquiet,
sy, and trf strip a leading neutral double quote from their final
arguments to allow embedding of leading spaces. All such arguments
are "strings" in a general sense, representing character sequences,
file names, operating system commands, or parameters to an output
device extension command. To include a double quote inside a
quoted argument, use the \[dq] special character escape sequence
(which also serves to typeset the glyph in text).
\ A backslash introduces an escape sequence. The escape character
can be changed with the ec request; eo disables escape sequence
recognition. Use the \[rs] special character escape sequence to
format a backslash glyph, and \e to typeset the glyph of the
current escape character.
( An opening parenthesis is special only in certain escape sequences;
when recognized, it introduces an argument of exactly two
characters. groff offers the more flexible square bracket syntax.
[ An opening bracket is special only in certain escape sequences;
when recognized, it introduces an argument (list) of any length,
not including a closing bracket.
] A closing bracket is special only when an escape sequence using an
opening bracket as an argument delimiter is being interpreted. It
ends the argument (list).
Additionally, the Control+A character (U+0001) in text is interpreted
as a leader (see below).
Horizontal whitespace characters are significant to groff, but trailing
spaces on text lines are ignored.
space On control lines and within bracketed escape sequences, spaces
separate arguments. On text lines, 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 (the default), inter-word spaces are
expanded until the output line reaches the configured length.
An adjustable but non-breaking space is available with \~. To
get a space of fixed width, use one of the escape sequences
`\ ' (the escape character followed by a space), \0, \|, \^,
or \h; see section "Escape sequences" below.
newline On text lines, a newline formats an inter-word space and, if
filling is enabled, triggers end-of-sentence recognition on
the preceding text. See section "Line continuation" below.
tab A tab character on a text line causes the drawing position to
advance to the next defined tab stop.
Sentences
Configure the sets of characters that potentially end sentences or are
transparent to sentence endings with the cflags request. Use the ss
request to change--or eliminate--supplemental inter-sentence space.
Tabs and leaders
The formatter interprets input horizontal tab characters ("tabs") and
Control+A characters ("leaders") into movements to the next tab stop.
Tabs simply move to the next tab stop; leaders place enough periods to
fill the space. Tab stops are by default located every half inch
measured from the drawing position corresponding to the beginning of
the input line; see section "Page geometry" of roff(7). Tabs and
leaders do not cause breaks and therefore do not interrupt filling.
Tab stops can be configured with the ta request, and tab and leader
glyphs with the tc and lc requests, respectively.
Line continuation
When filling is enabled, input and output line breaks generally do not
correspond. The roff language therefore distinguishes input and output
line continuation.
A backslash \ immediately followed by a newline, sometimes discussed as
\newline, suppresses the effects of that newline on the input. The
next input line thus retains the classification of its predecessor as a
control or text line. \newline is useful for managing line lengths in
the input during document maintenance; you can break an input line at a
space, or in the middle of a word, request invocation, macro call, or
escape sequence. Input line continuation is invisible to the
formatter, with two exceptions: the | operator recognizes the new input
line, and the input line counter register .c increments.
The \c escape sequence continues an output line. Nothing on the input
line after it is formatted. In contrast to \newline, a line after \c
is treated as a new input line, so a control character is recognized at
its beginning. The visual results depend on whether filling is
enabled. An intervening control line that causes a break overrides \c,
flushing out the pending output line in the usual way. The register
.int interpolates a positive value only if the pending output line has
been continued with \c; this datum is associated with the environment.
Colors
groff supports color output with a variety of color spaces and up to 16
bits per channel. Some devices, particularly terminals, may be more
limited. When color support is enabled, two colors are current at any
given time: the stroke color, with which glyphs, rules (lines), and
geometric objects like circles and polygons are drawn, and the fill
color, which can be used to paint the interior of a closed geometric
figure. The color, defcolor, gcolor, and fcolor requests; \m and \M
escape sequences; and .color, .m, and .M registers exercise color
support.
Each output device has a color named "default", which cannot be
redefined. A device's default stroke and fill colors are not
necessarily the same. For the dvi, html, pdf, ps, and xhtml output
devices, troff automatically loads a macro file defining many color
names at startup. By the same mechanism, the devices supported by
grotty(1) recognize the eight standard ISO 6429/ECMA-48 color names.
(These are known vulgarly as "ANSI" colors, after its X3.64 standard,
now withdrawn.)
Measurements
Express numeric parameters that specify measurements as integers or
decimal fractions with an optional scaling unit suffixed. A scaling
unit is a letter that immediately follows the magnitude of a
measurement. Digits after the decimal point are optional.
The formatter scales measurements by the specified scaling unit,
storing them internally (with any fractional part discarded) in basic
units. The device resolution can therefore be obtained by storing a
value of "1i" to a register, then reading the register.
u Basic unit; it is at least as small as any other unit.
i Inch; defined as 2.54 centimeters.
c Centimeter.
p Point; a typesetter's unit used for measuring type size. There
are 72 points to an inch.
P Pica; another typesetter's unit. There are 6 picas to an inch
and 12 points to a pica.
z Typographical point; like p, but used only with type sizes, to
overcome a limitation of AT&T troff.
s Scaled point.
f Multiplication by 65,536; scales decimal fractions in the
interval [0, 1] to 16-bit unsigned integers.
The magnitudes of other scaling units depend on the text formatting
parameters in effect.
m Em; an em is equal to the current type size in points.
n En; on typesetters, an en is one-half em, but on terminals an en
equals an em.
v Vee; distance between text baselines.
M Hundredth of an em.
Motion quanta
The basic unit u is not necessarily an output device's smallest
addressable length; u can be smaller to avoid integer rounding errors.
The minimum distances that a device can work with in the horizontal and
vertical directions are termed its motion quanta, stored in the .H and
.V registers, respectively. The formatter rounds measurements to
applicable motion quanta. Half-quantum fractions round toward zero.
Default units
A general-purpose register (one created or updated with the nr request;
see section "Registers" below) is implicitly dimensionless, or reckoned
in basic units if interpreted in a measurement context. But it is
convenient for many requests and escape sequences to infer a scaling
unit for an argument if none is specified. An explicit scaling unit
(not after a closing parenthesis) can override an undesirable default.
Effectively, the default unit is suffixed to the expression if a
scaling unit is not already present. GNU troff's use of integer
arithmetic in numeric expressions should also be kept in mind.
Numeric expressions
When evaluated, a numeric expression interpolates an integer. GNU
troff recognizes the following operators.
+ addition
- subtraction
* multiplication
/ truncating division
% modulus
--------------------------------------------
unary + assertion, motion, incrementation
unary - negation, motion, decrementation
--------------------------------------------
; scaling
>? maximum
<? minimum
--------------------------------------------
< less than
> greater than
<= less than or equal
>= greater than or equal
= equal
== equal
--------------------------------------------
& logical conjunction ("and")
: logical disjunction ("or")
! logical complementation ("not")
--------------------------------------------
( ) precedence
--------------------------------------------
| boundary-relative measurement
troff provides a set of mathematical and logical operators familiar to
programmers--as well as some unusual ones--but supports only integer
arithmetic. (Provision is made for interpreting and reporting decimal
fractions in certain cases.) The internal data type used for computing
results depends on the host machine but is at least a 32-bit signed
integer, which suffices to represent magnitudes within a range of +-2
billion. (If that's not enough, see groff_tmac(5) for the 62bit.tmac
macro package.) Arithmetic saturates. (If overflow would occur, GNU
troff emits a warning in category "range". See section "Warnings" of
troff(1).)
Arithmetic infix operators perform a function on the numeric
expressions to their left and right; they are + (addition), -
(subtraction), * (multiplication), / (truncating division), and %
(modulus). Truncating division rounds to the integer nearer to zero,
no matter how large the fractional portion. Division and modulus by
zero are errors and abort evaluation of a numeric expression.
Arithmetic unary operators operate on the numeric expression to their
right; they are - (negation) and + (assertion--for completeness; it
does nothing). The unary minus must often be used with parentheses to
avoid confusion with the decrementation operator, discussed below.
The sign of the modulus of operands of mixed signs is determined by the
sign of the first. Division and modulus operators satisfy the
following property: given a dividend a and a divisor b, a quotient q
formed by "(a / b)" and a remainder r by "(a % b)", then qb + r = a.
GNU troff's scaling operator, used with parentheses as (c;e), evaluates
a numeric expression e using c as the default scaling unit. If c is
omitted, scaling units are ignored in the evaluation of e. GNU troff
also provides a pair of operators to compute the extremum of two
operands: >? (maximum) and <? (minimum).
Comparison operators comprise < (less than), > (greater than), <= (less
than or equal), >= (greater than or equal), and = (equal, with a
synonym ==). When evaluating a comparison, the formatter replaces it
with "0" if it is false and "1" if true. In the roff language,
positive values are true, others false.
Operate on truth values with the logical operators & (logical
conjunction or "and") and : (logical disjunction or "or"). They
evaluate as comparison operators do. A logical complementation ("not")
operator, !, works only within "if", "ie", and "while" requests.
Furthermore, the formatter recognizes ! only at the beginning of a
numeric expression not contained by another numeric expression. In
other words, ! must be the "outermost" operator. Its presence
elsewhere causes the expression to evaluate false. (GNU troff emits a
warning in category "number". See section "Warnings" of troff(1).)
This unfortunate limitation maintains compatibility with AT&T troff.
Test a numeric expression for falsity within a complex expression by
comparing it to a false value.
The roff language has no operator precedence: expressions are evaluated
strictly from left to right, in contrast to schoolhouse arithmetic.
Use parentheses ( ) to impose a desired precedence upon subexpressions.
For many requests and escape sequences that cause motion on the page,
the unary operators + and - work differently when leading a numeric
expression. They then indicate a motion relative to the drawing
position: positive is down in vertical contexts, right in horizontal
ones.
+ and - are also treated differently by the following requests and
escape sequences: bp, in, ll, pl, pn, po, ps, pvs, rt, ti, \H, \R, and
\s. Here, leading plus and minus signs serve as incrementation and
decrementation operators, respectively. To negate an expression in
these contexts, subtract it from zero or include the unary minus in
parentheses with its argument.
A leading | operator indicates a motion relative not to the drawing
position but to a boundary. For horizontal motions, the measurement
specifies a distance relative to a drawing position corresponding to
the beginning of the input line. By default, tab stops reckon
movements in this way. Most escape sequences do not; | tells them to
do so. For vertical motions, the | operator specifies a distance from
the first text baseline on the page or in the current diversion, using
the current vertical spacing.
The delimited escape sequence \B tests its argument for validity as a
numeric expression.
A register interpolated as an operand in a numeric expression must have
an Arabic format; luckily, this is the default.
Because spaces separate arguments to requests, spaces are not allowed
in numeric expressions unless parentheses surround the (sub)expression
containing them.
Identifiers
An identifier labels a GNU troff datum such as a register, name (macro,
string, or diversion), typeface, color, special character or character
class, hyphenation language code, environment, or stream. Valid
identifiers consist of one or more ordinary characters. An ordinary
character is any Unicode Basic Latin character that is not a space and
not the escape character; recall section "Input format" above.
An identifier with a closing bracket ("]") in its name can't be
accessed with bracket-form escape sequences that expect an identifier
as a parameter. Similarly, the identifier "(" can't be interpolated
except with bracket forms.
Beginning a macro, string, or diversion name with the character "[" or
"]" forecloses use of the refer(1) preprocessor, which recognizes input
lines starting with ".[" and ".]" as bibliographic reference
delimiters.
The delimited escape sequence \A tests its argument for validity as an
identifier.
The formatter's handling of undefined identifiers is context-dependent.
There is no way to invoke an undefined request; such syntax is
interpreted as a macro call instead. If the identifier is interpreted
as a string, macro, or diversion name, the formatter defines it as
empty and interpolates nothing. (GNU troff emits a warning in category
"mac". See section "Warnings" of troff(1).) Similarly, if the
identifier is interpreted as a register name, the formatter initializes
it to zero and interpolates that value. GNU troff emits a warning in
category "reg"; see section "Warnings" in troff(1), and subsection
"Interpolating registers" and section "Strings" below. Attempting to
use an undefined typeface, special character or character class, color,
environment, hyphenation language code, or stream generally provokes an
error diagnostic.
Identifiers for requests, macros, strings, and diversions share one
name space; special characters and character classes another. No other
object types do.
Control characters
The formatter recognizes a control character only at the beginning of
an input line, or at the beginning of a branch of a control structure
request; see section "Control structures" below.
A few requests cause a break implicitly; invoke them with the no-break
control character to prevent the break. Break suppression is its sole
behavioral distinction. Employing the no-break control character to
invoke requests that don't cause breaks is harmless but poor style.
The control character "." and the no-break control character "'" can be
changed with the cc and c2 requests, respectively. Within a macro
definition, register .br indicates the control character used to call
it.
Invoking requests
A control character is optionally followed by tabs and/or spaces and
then an identifier naming a request or macro. The invocation of an
unrecognized request is interpreted as a macro call. Defining a macro
with the same name as a request replaces the request. Deleting a
request name with the rm request makes it unavailable. The als request
can alias requests, permitting them to be wrapped or non-destructively
replaced. See section "Strings" below.
There is no inherent limit on argument length or quantity. Most
requests take one or more arguments, and ignore any they do not expect.
A request may be separated from its arguments by tabs or spaces, but
only spaces can separate an argument from its successor. Only one
between arguments is necessary; any excess is ignored. GNU troff does
not allow tabs for argument separation. (Plan 9 troff does.)
Generally, a space within a request argument is not relevant, not
meaningful, or is supported by bespoke provisions, as with the tl
request's delimiters. Some requests, like ds, interpret the remainder
of the control line as a single argument. See section "Strings" below.
Spaces and tabs immediately after a control character are ignored.
Commonly, authors use them to indent the source of documents or macro
files.
Calling macros
If a macro of the desired name does not exist when called, the
formatter creates it and assigns it an empty definition. (GNU troff
emits a warning in category "mac". See section "Warnings" in
troff(1).) Calling an undefined macro does end a macro definition
naming it as its end macro (see section "Writing macros" below).
To embed spaces within a macro argument, enclose the argument in
neutral double quotes `"'. Horizontal motion escape sequences are
sometimes a better choice for arguments to be formatted as text.
The foregoing raises the question of how to embed neutral double quotes
or backslashes in macro arguments when those characters are desired as
literals. In GNU troff, the special character escape sequence \[rs]
produces a backslash and \[dq] a neutral double quote.
In GNU troff's AT&T compatibility mode, these characters remain
available as \(rs and \(dq, respectively. AT&T troff did not
consistently define these special characters, but its descendants can
be made to support them. See groff_font(5). If even that is not
feasible, see the "Calling Macros" section of the groff Texinfo manual
for the complex macro argument quoting rules of AT&T troff.
Using escape sequences
Whereas requests must occur on control lines, escape sequences can
occur intermixed with text and may appear in arguments to requests,
macros, and other escape sequences. An escape sequence is introduced
by the escape character, a backslash \. The next character selects the
escape's function.
Escape sequences 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 scheme, 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 scheme, the user selects a delimiter
character. A few escape sequences are idiosyncratic, and support both
of the foregoing conventions (\s), designate their own termination
sequence (\?), consume input until the next newline (\!, \", \#), or
support an additional modifier character (\s again, and \n). In no
case can an escape sequence parameter contain an unescaped newline.
If the character that follows the escape character does not identify a
defined operation, the formatter ignores the escape character. (GNU
troff emits a warning in category "escape". See section "Warnings" in
troff(1).)
Escape sequence interpolation is of higher precedence than escape
sequence argument interpretation. This rule affords flexibility in
using escape sequences to construct parameters to other escape
sequences.
The escape character can be interpolated (\e). Requests permit the
escape mechanism to be deactivated (eo) and restored, or the escape
character changed (ec), and to save and restore it (ecs and ecr).
Delimiters
Some escape sequences that require parameters use delimiters. The
neutral apostrophe ' is a popular choice and shown in this document.
The neutral double quote " is also commonly seen. Punctuation
characters are the best choice (and most portable to other troffs,
except for those meaningful in numeric expressions; see below.
The following escape sequences are not themselves delimited, and thus
are allowed as delimiters: \space, \%, \|, \^, \{, \}, \', \`, \-, \_,
\!, \?, \), \/, \,, \&, \:, \~, \0, \a, \c, \d, \e, \E, \p, \r, \t, and
\u. However, we discourage using them this way; they can make the
input confusing to read. (The eqn(1) and tbl(1) preprocessors use
parameterized but non-delimited special character escape sequences \(
and \[ to bracket portions of their output.) An invalid escape
sequence is valid as a delimiter if the character after the escape
character would be valid.
The escape sequences \D, \h, \H, \l, \L, \N, \R, \s, \S, \v, and \x
prohibit delimiters that are meaningful in numeric expressions, because
they accept numeric expressions as (or within) their arguments. For
consistency, GNU troff prohibits the same delimiters in the argument to
the tl request. The "if", ie, and "while" requests each interpret
their first argument as a conditional expression; only characters that
are not meaningful as operators in that context can be used as output
comparison delimiters. The following inputs are therefore invalid as
delimiters in GNU troff.
o the numerals 0-9 and the decimal point "."
o the (single-character) operators +-/*%<>=&:()|
o any escape sequences other than \%, \:, \{, \}, \', \`, \-,
\_, \!, \/, \c, \e, and \p
Delimiter syntax is flexible (and laborious to describe) primarily for
historical reasons; the foregoing restrictions need be kept in mind
mainly when using GNU troff in AT&T compatibility mode. Normally, GNU
troff keeps track of the nesting depth of escape sequence
interpolations, so the only characters you need to avoid using as
delimiters are those that appear in the arguments you input, not those
that result from interpolation. Typically, ' works fine. See section
"Implementation differences" in groff_diff(7).
Dummy characters
As discussed in roff(7), the first character on an input line is
treated specially. Further, formatting a glyph has many consequences
on formatter state (see section "Environments" below). Occasionally,
we want to escape this context or embrace some of those consequences
without actually rendering a glyph to the output. \& interpolates a
dummy character, which is constitutive of output but invisible. Its
presence alters the interpretation context of a subsequent input
character, and enjoys several applications: preventing the insertion of
extra space after an end-of-sentence character, preventing
interpretation of a control character at the beginning of an input
line, preventing kerning between two glyphs, and permitting the tr
request to remap a character to "nothing". \) works as \& does, except
that it does not cancel a pending end-of-sentence state.
Page control
Discretionary page breaks can prevent the unwanted separation of
content. A new page number takes effect during page ejection; see
subsection "The implicit page trap" below. The bp request breaks the
page, incrementing the page number by one (or setting it per the
supplied argument). The ne request forces a page break if insufficient
vertical space is available (it asserts "needed" space). sv requires
vertical space as ne does, but also saves it for later output by the os
request.
The nl register interpolates the vertical drawing position as of the
most recently typeset output line. It does not necessarily (and often
does not) represent that of the pending output line, because the
formatter does not determine the position of its baseline until it is
output. Assigning a value to nl sets the vertical drawing position in
advance of further modifications to baseline positioning arising from
alterations to type size, changes to vertical spacing, or application
of extra pre- or post-vertical spacing.
When the formatter starts, the transition to the first page has not yet
happened--nl is negative. If you plant a page location trap at
vertical position "0" (idiomatically to format a header), you can
assign a negative value to nl to spring that trap even if the page has
already started (see subsection "Page location traps" below).
Control structures
groff has "if" and "while" control structures like other languages.
However, the syntax for grouping multiple input lines in the branches
or bodies of these structures is unusual.
They have a common form: the request name is (except for el "else")
followed by a conditional expression cond-expr; the remainder of the
line, input, is interpreted as if it were an input line. Any quantity
of spaces between arguments to requests serves only to separate them;
leading spaces in input are therefore not seen. input effectively
cannot be omitted; if cond-expr is true and input is empty, the newline
at the end of the control line is interpreted as a blank line (and
therefore a blank text line).
It is frequently desirable for a control structure to govern more than
one request, macro call, or text line, or combination of the foregoing.
The opening and closing brace escape sequences \{ and \} perform such
grouping. Brace escape sequences outside of control structures have no
meaning and produce no output.
\{ should appear (after optional spaces and tabs) immediately
subsequent to the request's conditional expression. \} should appear
on a line with other occurrences of itself as necessary to match \{
sequences. It can be preceded by a control character, spaces, and
tabs. Input after any quantity of \} sequences on the same line is
processed only if all the preceding conditions to which they correspond
are true. Furthermore, a \} closing the body of a "while" request must
be the last such escape sequence on an input line.
GNU troff treats the body of a "while" request similarly to that of a
de request (albeit one not read in copy mode), but stores it under an
internal name and deletes it when the loop finishes. The operation of
a macro containing a "while" request can slow significantly if its body
is large. Each time GNU troff interpolates the macro, it parses and
stores the "while" body again. An often better solution--and one that
is more portable, since AT&T troff lacked the "while" request--is to
instead write a recursive macro, which is parsed only once (unless you
redefine it). To prevent infinite loops, GNU troff limits the default
number of available recursion levels to 1,000 or somewhat less (because
things other than macro calls can be on the input stack). You can
disable this protective measure, or alter the limit, by setting the
slimit register. See section "Debugging" below.
Conditional expressions
The "if", ie, and "while" requests test the truth values of numeric
expressions. They also support several additional Boolean operators;
the members of this expanded class are termed conditional expressions;
their truth values are as shown below.
cond-expr... ...is true if...
------------------------------------------------------------------------
' s1 ' s2 ' s1 produces the same formatted output as s2 .
c g a character g is defined.
d m a string, macro, diversion, or request m is defined.
e the current page number is even.
F f a font named f is available.
m c a color named c is defined.
n the formatter is in nroff mode.
o the current page number is odd.
r n a register named n is defined.
S s a font style named s is available.
t the formatter is in troff mode.
v n/a (historical artifact; always false).
If the first argument to an "if", ie, or "while" request begins with a
non-alphanumeric character apart from "!" (see below) and is not a
numeric expression, the formatter performs an output comparison test.
Shown first in the table above, the output comparison operator
interpolates a true value if formatting its comparands s1 and s2
produces the same output commands. Other delimiters can be used in
place of the neutral apostrophes; see section "Delimiters" above.
troff formats s1 and s2 in separate scratch buffers; after comparison,
it discards the resulting data. The resulting glyph properties,
including font family, style, size, and slant, must match, but not
necessarily the requests and/or escape sequences used to obtain them.
Motions must match in orientation and magnitude to within the
applicable horizontal or vertical motion quantum of the device, after
rounding.
Surround the comparands with \? to avoid formatting them; this causes
them to be compared character by character, as with string comparisons
in other programming languages. Since GNU troff reads comparands
protected with \? in copy mode, they need not be syntactically valid.
The escape character is still lexically recognized, however, and
consumes the next character.
The above operators can't be combined with most others, but a leading
"!", not followed immediately by spaces or tabs, complements an
expression. Spaces and tabs are optional immediately after the "c",
"d", "F", "m", "r", and "S" operators, but right after "!", they end
the predicate and the conditional evaluates true. (This bizarre
behavior maintains compatibility with AT&T troff.)
Conditional operators do not create roff language objects as
interpolations with \n and \* escape sequences do.
Syntax reference conventions
In the following request and escape sequence specifications, most
argument names were chosen to be descriptive. GNU troff reads
arguments named character-sequence, command, contents, file, and
message in copy mode (see section "Copy Mode" below) until the end of
the input line. A character-sequence comprises one or more ordinary,
special, or indexed characters; spaces; or escape sequences that
interpolate only these. We name the remaining arguments for clarity;
they are also character-sequences. A neutral double quote `"' can
optionally prefix a character-sequence; the formatter discards one if
present, permitting initial embedded spaces in the argument. input
refers to arbitrary character sequences (up to a newline or delimiter)
that GNU troff fully interprets, in contrast to copy mode.
A few denotations are more specific.
b is a numerical expression evaluated as a Boolean;
positive values are true, others false.
c denotes a single character--ordinary, special, or
indexed.
command is an instance of contents (see below) to be passed
to the system as a command (potentially with
arguments). GNU troff strips a leading neutral
double quote, allowing embedded leading spaces.
contents is arbitrary input, excluding an unescaped newline,
read in copy mode. GNU troff strips a leading
neutral double quote, allowing embedded leading
spaces.
div is a diversion identifier.
env is an environment identifier.
file is an instance of contents naming a file on the
system. GNU troff strips a leading neutral double
quote, allowing embedded leading spaces. GNU troff
does not accept newlines (line feeds) in file names
supplied as arguments to requests.
font is a typeface specified as a font identifier, an
abstract style, or a mounting position.
ident is a valid groff identifier; its use often indicates
that the operation creates an object of a type
subsequently referred to as mac, reg, str, and so
forth.
mac is a macro identifier.
message is an instance of contents to emit on the standard
error stream. GNU troff strips a leading neutral
double quote, allowing embedded leading spaces.
n is a numeric expression that evaluates to a non-
negative integer.
+-N is a numeric expression with a meaning dependent on
its sign; see below.
name is a macro, string, or diversion identifier, or the
name of a request.
npl is a numeric expression constituting a count of
subsequent productive input lines; that is, those
that directly produce formatted output. Text lines
produce output, as do control lines containing
requests like ".tl //Page %//" or escape sequences
like "\l'1i'". Macro calls are not themselves
productive, but their interpolations can be.
reg is a register identifier.
str is a string identifier.
stream is an output stream identifier.
If a numeric expression presented as +-N starts with a `+' sign, an
increment in the amount of of N is applied to the value applicable to
the request or escape sequence. If it starts with a `-' sign, a
decrement of magnitude N is applied instead. Without a sign, N
replaces any existing value. A roff formatter always interprets a
leading minus sign in N as a decrementation operator, not an algebraic
sign. To assign a register a negative value or the negated value of
another interpolation, you must force the formatter to interpret "-" as
a negation or minus, rather than decrementation, operator: enclose the
"-" with its operand in parentheses or subtract the expression of
interest from zero. If a prior value does not exist--the register was
undefined--an increment or decrement applies as if to 0.
Request short reference
Not all details of request behavior are outlined here. See the groff
Texinfo manual or, for features new to GNU troff, groff_diff(7).
.ab Abort the formatter; exit with failure status.
.ab terminal-message
Abort the formatter; write terminal-message to the standard
error stream and exit with failure status.
.ad Enable output line alignment and adjustment using the mode
stored in \n[.j].
.ad c Enable output line alignment and adjustment in mode c
(c=b,c,l,n,r). Sets \n[.j].
.af reg c Assign format c to register reg, 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 basic
Latin alphabetics, respectively, in the lettercase
specified. The default is 0.
.aln new-register existing-register
Create alias (additional name) new-register of
existing-register, causing the names to refer to the same
stored object. If existing-register is undefined, the
formatter ignores the request. GNU troff emits a warning in
category "reg".
.als new-name existing-name
Create alias (additional name) new-name of request, string,
macro, or diversion existing-name, causing the names to
refer to the same stored object. If existing-name is
undefined, the formatter ignores the request. GNU troff
emits a warning in category "mac". If new-name already
exists, its definition is lost unless already aliased.
.am mac Append to macro mac until encountering ".." at the start of
a control line in the current conditional block.
.am mac end-mac
Append to macro mac until end-mac is called at the start of
a control line in the current conditional block. end-mac
can be a request.
.am1 mac As "am", with compatibility mode disabled when the
appendment to macro mac is interpreted.
.am1 mac end-mac
As ".am mac", with compatibility mode disabled when the
appendment to macro mac is interpreted.
.ami str Append to a macro indirectly--its name is in string
str--until encountering "..".
.ami str end-mac-str
Append to a macro indirectly. As "am", but str and
end-mac-str contain the names of the macro to be appended
to, and that whose call ends the appendment, respectively.
.ami1 str As ami, with compatibility mode disabled when the appendment
is interpreted.
.ami1 str end-mac-str
As ami, with compatibility mode disabled when the appendment
is interpreted.
.as ident Create string ident with empty contents; no operation if
ident already exists.
.as str contents
Append contents to string str.
.as1 ident As ".as ident".
.as1 str contents
As "as", with compatibility mode disabled when the
appendment to string str is interpreted.
.asciify div
Unformat ordinary characters, spaces, and some escape
sequences in diversion div. When transforming a glyph node
back into an input sequence that demands expression as a
special character escape sequence, GNU troff uses the
default escape character.
.backtrace Write the state of the input stack to the standard error
stream. See the groff(7).
.bd font Stop emboldening font font.
.bd font n Embolden font by overstriking its glyphs offset by n-1
units. See register .b.
.bd special-font font
Stop emboldening special-font when font is selected.
special-font must be a font name, not a mounting position.
.bd special-font font n
Embolden special-font, overstriking its glyphs offset by n-1
units when font is selected. See register .b.
.blm Unset blank line macro (trap). Restore default handling of
blank lines.
.blm mac Set blank line macro (trap) to mac.
.box Stop directing output to current diversion; any pending
output line is discarded.
.box ident Direct output to diversion ident, omitting a partially
collected line.
.boxa Stop appending output to current diversion; any pending
output line is discarded.
.boxa div Append output to diversion div, omitting a partially
collected line.
.bp Break page and start a new one.
.bp +-N Break page, starting a new one numbered +-N.
.br Break output line.
.brp Break and force adjustment of the output line per the
current adjustment mode.
.break Break out of a "while" loop.
.c2 Reset no-break control character to "'".
.c2 o Recognize ordinary character o as no-break control
character.
.cc Reset control character to `.'.
.cc o Recognize ordinary character o as the control character.
.ce Break, center the output of the next productive input line
without filling, and break again.
.ce npl Break, center the output of the next npl productive input
lines without filling, then break again. If npl <= 0, stop
centering.
.cf file Break and copy contents of file as "throughput" to GNU troff
output (see groff_out(5)). Each line of file is output as
if preceded by \!, but is not interpreted by the formatter.
Unsafe request; disabled by default.
.cflags n c...
Assign properties encoded by non-negative integer n to each
character or class c. Spaces need not separate c arguments.
.ch mac Unplant page location trap mac.
.ch mac vertical-position
Change page location trap mac planted by wh by moving its
location to vertical-position (default scaling unit v).
.char c Define an ordinary, special, or indexed character c as
empty.
.char c contents
Define an ordinary, special, or indexed character c as
contents.
.chop name Remove the last character from the macro, string, or
diversion name.
.class ident c ...
Define a (character) class ident comprising the characters
or range expressions c, where each c is an ordinary,
special, or indexed character; or a range expression. A
class thus defined can then be referred to in a cflags
request in lieu of listing all the characters within it.
.close stream
Close stream, making it unavailable for "write" requests.
.color Enable output of color-related device-independent output
commands. It is enabled by default.
.color b Enable or disable output of color-related device-independent
output commands per Boolean expression b.
.composite c
Remove composite character mapping for character c.
.composite c1 c2
Map character c1 to c2 when c1 is a combining component in a
composite character.
.continue Skip the remainder of a "while" loop's body, immediately
retesting its conditional expression.
.cp Enable AT&T troff compatibility mode. It is disabled by
default.
.cp b Enable or disable AT&T troff compatibility mode per Boolean
expression b.
.cs f Disable constant-width glyph spacing mode for font f.
.cs f n Enable constant-width glyph spacing mode for font f at n/36
ems.
.cs f n p Enable constant-width glyph spacing mode for font at n/36
ems, as if one em equals p scaled points.
.cu Continuously underline the output of the next productive
input line.
.cu npl Continuously underline the output of the next npl productive
input lines. If npl=0, stop continuously underlining.
.da Stop appending output to current diversion.
.da div Append output to diversion div.
.de ident Define macro ident until ".." occurs at the start of a
control line in the current conditional block.
.de ident end-mac
Define macro ident until end-mac is called at the start of a
control line in the current conditional block. end-mac can
be a request.
.de1 ident As de, with compatibility mode disabled when mac is
interpreted.
.de1 ident end-mac
As ".de ident end-mac", with compatibility mode disabled
when mac is interpreted.
.defcolor ident scheme color-component ...
Define a color named ident. scheme identifies a color space
and determines the number of required color-components; it
must be one of "rgb" (three components), "cmy" (three),
"cmyk" (four), or "gray" (one). "grey" is accepted as a
synonym of "gray". The color components can be encoded as a
single hexadecimal value starting with # or ##. The former
indicates that each component is in the range 0-255 (0-FF),
the latter the range 0-65,535 (0-FFFF). Alternatively, each
color component can be specified as a decimal fraction in
the range 0-1, interpreted using a default scaling unit
of "f", which multiplies its value by 65,536 (but clamps it
at 65,535).
.dei str Define macro indirectly. As de, but interpolate string str
to obtain the macro's name.
.dei str end-mac-str
Define macro indirectly. As de, but str and end-mac-str
contain the names of the macro to be defined, and that whose
call ends the definition, respectively.
.dei1 str As dei, with compatibility mode disabled when the macro is
interpreted.
.dei1 str end-mac-str
As dei, with compatibility mode disabled when the macro is
interpreted.
.device character-sequence
Embed character-sequence into GNU troff output as parameters
to an "xX" device extension command; see groff_out(5). The
output driver or other postprocessor interprets
character-sequence as it sees fit.
.devicem name
Write contents of macro or string name to troff output as
the argument to a device extension command.
.di Stop directing output to current diversion.
.di ident Direct output to diversion ident.
.do name argument ...
Interpret the string, request, diversion, or macro name
(along with any further arguments) with compatibility mode
disabled. Compatibility mode is restored (only if it was
active) when the interpolation of name is interpreted.
.ds ident Create empty string named ident.
.ds ident contents
Create a string named ident containing contents.
.ds1 ident
.ds1 ident contents
As ds, with compatibility mode disabled when the string is
interpreted.
.dt Clear diversion trap.
.dt vertical-position mac
Set the diversion trap to macro mac at vertical-position
(default scaling unit v).
.ec Recognize \ as the escape character.
.ec o Recognize ordinary character o as the escape character.
.ecr Restore escape character saved with ecs.
.ecs Save the escape character.
.el Interpolate a newline if the conditional expression of the
corresponding ie request was false.
.el input Interpret input as if it were an input line if the
conditional expression of the corresponding ie request was
false.
.em Unset end-of-input macro.
.em mac Call macro mac after the end of input.
.eo Disable the escape mechanism in interpretation mode.
.ev Pop environment stack, returning to previous one.
.ev env Push current environment onto stack and switch to env,
creating it if necessary.
.evc env Copy environment env to the current one.
.ex Exit the formatter.
.fam Set default font family to previous value.
.fam name Set default font family to name.
.fc Disable field mechanism.
.fc c Set field delimiter to c and pad glyph to space.
.fc c1 c2 Set field delimiter to c1 and pad glyph to c2.
.fchar c Define fallback character c as empty.
.fchar c contents
Define fallback character c as contents. As char, but while
that request hides a glyph with the same name in the
selected font, fchar definitions are used only if the font
lacks a glyph for c. GNU troff performs this test before
searching special fonts.
.fcolor Restore previous fill color, or the default if there is
none.
.fcolor col
Select col as the fill color.
.fi Enable filling of output lines; a pending output line is
broken. Sets \n[.u].
.fl Flush any pending output line.
.fp pos id Mount font with font description file name id at non-
negative position pos.
.fp pos id font-description-file-name
Mount font with font-description-file-name as name id at
non-negative position pos.
.fschar f c
Define fallback character c specific to font f as empty.
.fschar f c contents
Define fallback character c specific to font f as contents.
As char, but GNU troff locates a character defined by fschar
after any fonts named as arguments to the fspecial are
searched and before those named as arguments to the
"special" request.
.fspecial f
Empty the list of fonts treated as special when f is
selected.
.fspecial f s ...
Declare each font s as special only when font f is selected.
GNU troff searches fonts specified as arguments to the
"special" request after those given as arguments to the
fspecial request.
.ft
.ft P Select the typeface font. If font is an integer, the
formatter interprets it as a mounting position; the font
mounted there is selected. If that position refers to an
abstract style, GNU troff combines it with the default
family (see fam above and \F below) to make a resolved font
name. If font is "DESC", if the mounting position is not an
abstract style and no font is mounted there, or the mounting
position is negative, GNU troff ignores the request. (It
also emits a warning in category "font", or "range", as
appropriate. See section "Warnings" in troff(1).) Also see
\f .
.ftr f Remove translation of font named f.
.ftr f1 f2 Translate font name f1 to f2.
.fzoom font 0
Stop magnifying font.
.fzoom font zoom
Set magnification of mounted font to zoom, a multiplier of
the current type size in thousandths (default: 1000).
.gcolor Restore previous stroke color, or the default if there is
none.
.gcolor col
Select col as the stroke color.
.hc Reset the hyphenation character to \% (the default).
.hc c Change the hyphenation character to c.
.hcode dst1 src1 [dst2 src2] ...
Set the hyphenation code of character dst1 to that of src1,
and so on.
.hla Clear the environment's hyphenation language (disabling
automatic hyphenation).
.hla ident Set the environment's hyphenation language to ident.
.hlm Set the consecutive automatically hyphenated line limit to
-1 (the default), meaning "no limit".
.hlm n Set the consecutive automatically hyphenated line limit to
to n. A negative value means "no limit".
.hpf file Read hyphenation patterns from file.
.hpfa file Append hyphenation patterns from file.
.hpfcode a b [c d] ...
Caution: This request will be withdrawn in a future groff
release. Use hcode instead.
Define mappings for character codes in hyphenation pattern
files.
.hw word ...
Define each argument word (comprising ordinary, special, or
indexed characters) as a hyphenation exception word such
that each occurrence of a hyphen-minus "-" in word indicates
a hyphenation point.
.hy Set automatic hyphenation mode to the value of the
.hydefault register.
.hy 0 Disable automatic hyphenation; same as .nh.
.hy mode Set automatic hyphenation mode to mode; see section
"Hyphenation" below.
.hydefault mode
Set hyphenation mode default 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 unit m).
.hys Set the hyphenation space to 0 (the default).
.hys hyphenation-space
Suppress automatic hyphenation in adjustment modes "b" or
"n" if that adjustment can be achieved by adding no more
than hyphenation-space to each inter-word space (default
scaling unit m).
.ie cond-expr
Interpolate a newline if cond-expr is true, otherwise skip
to a corresponding el request.
.ie cond-expr input
If cond-expr is true, interpret input as if it were an input
line, otherwise skip to a corresponding el request.
.if cond-expr
Interpolate a newline if cond-expr is true.
.if cond-expr input
If cond-expr is true, then interpret input as if it were an
input line.
.ig Ignore input (except for side effects of \R on auto-
incrementing registers) until ".." occurs at the start of a
control line in the current conditional block.
.ig end-mac
Ignore input (except for side effects of \R on auto-
incrementing registers) until end-mac is called at the start
of a control line in the current conditional block. end-mac
can be a request.
.in Set indentation amount to previous value.
.in +-N Set indentation to +-N (default scaling unit m).
.it Cancel any pending input line trap.
.it npl mac
Set (or replace) an input line trap in the environment,
calling mac after the next npl productive input lines have
been read. Lines interrupted with the \c escape sequence
are counted separately.
.itc Cancel any pending input line trap.
.itc npl mac
As "it", but lines interrupted with the \c escape sequence
do not apply to the line count.
.kern Enable pairwise kerning.
.kern b Enable or disable pairwise kerning per Boolean expression b.
.lc Unset leader repetition character.
.lc c Set leader repetition character to c (default: ".").
.length reg contents
Compute the number of characters in contents and store the
count in the register reg.
.linetabs Activate line-tabs in the environment. It is disabled by
default.
.linetabs b
Activate or deactivate line-tabs in the environment per
Boolean expression b.
.lf input-line-number
Set the input line number the formatter uses when reporting
diagnostics. The argument becomes the input line number of
the next line the formatter reads.
.lf input-line-number character-sequence
As lf with one argument, but also update the reported file
name to character-sequence.
.lg Enable ligature mode 1.
.lg m Set ligature mode to m (0 = disable, 1 = enable, 2 = enable
for two-letter ligatures only).
.ll Set line length to previous value. Does not affect a
pending output line.
.ll +-N Set line length to +-N (default length 6.5i, default scaling
unit m). Does not affect a pending output line.
.lsm Unset the leading space macro (trap). Restore default
handling of lines with leading spaces.
.lsm mac Set the leading space macro (trap) to mac.
.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 Set length of title lines to previous value.
.lt +-N Set length of title lines (default length 6.5i, default
scaling unit m).
.mc Cease writing margin character.
.mc c Begin writing margin character c to the right of each output
line at a distance of 10p.
.mc c d Begin writing margin character c on each output line at
distance d to the right of the right margin (default
distance 10p, default scaling unit m).
.mk Mark vertical drawing position in an internal register; see
.rt.
.mk reg Mark vertical drawing position in register reg.
.mso file As "so", except that GNU troff searches for the specified
file in the same directories as macro files; see
GROFFgroff(7) and -m
in section "Options" of the same page.
.msoquiet file
As mso, but no warning is emitted if file does not exist.
.na Disable output line adjustment.
.ne Break page if distance to next page location trap is less
than one vee.
.ne d Break page if distance to next page location trap is less
than distance d (default scaling unit v).
.nf Disable filling of output lines; a pending output line is
broken. Clears \n[.u].
.nh Disable automatic hyphenation; same as ".hy 0".
.nm Deactivate output line numbering.
.nm +-N
.nm +-N m
.nm +-N m s
.nm +-N m s i
Activate output line numbering: number the next output line
+-N, writing numbers every m lines (default 1), with s
numeral widths (\0) between the line number and the output
(default 1), and indenting the line number by i numeral
widths (default 0).
.nn Suppress numbering of the next output line counted by nm.
.nn n Suppress numbering of the next n output lines counted by nm.
If n=0, cancel suppression.
.nop Interpolate a newline.
.nop input Interpret input as if it were an input line.
.nr reg +-N
Define or update register reg with value N.
.nr reg +-N I
Define or update register reg with value N and auto-
increment I, which may be any integer.
.nroff Make the conditional expressions n true and t false.
.ns Enable no-space mode, ignoring .sp requests until a glyph or
\D primitive is output. See .rs.
.nx Stop processing the input file and read the next, if any.
.nx file Stop processing the input file and read file.
.open ident file
Open file for writing and associate a stream named ident
with it, making it available for "write" requests. Unsafe
request; disabled by default.
.opena ident file
As "open", but if file already exists, appends to it instead
of overwriting it. Unsafe request; disabled by default.
.os Output vertical space that was saved by the sv request.
.output character-sequence
Emit character-sequence "transparently" (directly) to
troff's output.
.pc Reset page number character to `%'.
.pc c Change the page number character used in titles to c.
.pchar c ...
Report, to the standard error stream, information about each
character (be it ordinary, special, or indexed) or character
class c. A character defined by a request (char, fchar,
fschar, or schar) reports its contents as a JSON-encoded
string, but the output is not otherwise in JSON format.
.pcolor Report, to the standard error stream, each defined color
name, its color space identifier, and channel value
assignments. A device's default stroke and/or fill colors,
"default", are not listed since they are immutable and their
details unknown to the formatter.
.pcolor col ...
Report, to the standard error stream, the name, color space
identifier, and channel value assignments of each color col.
.pcomposite
Report, to the standard error stream, the list of configured
composite character mappings. See the "composite" request.
The "from" code point is listed first, followed by its "to"
mapping.
.pev Report the state of the current environment followed by that
of all other environments to the standard error stream.
.pfp Report, to the standard error stream, the list of occupied
font mounting positions. Occupied mounting positions are
listed, one per line, in increasing order, followed by the
typeface name; if the name corresponds to an abstract style,
the entry ends there. Otherwise, the name of the font
description file and the font's "internal name" datum, the
meaning of which varies by output device, follow.
.pftr Report, to the standard error stream, the list of font
translations.
.phw Report, to the standard error stream, the list of
hyphenation exception words associated with the hyphenation
language selected by the hla request. A "-" marks each
hyphenation point. A word prefixed with "-" is not
hyphenated at all. The report suffixes words to which
automatic hyphenation applies (meaning those defined in a
hyphenation pattern file rather than with the hw request)
with a tab and asterisk "*".
.pi command
Pipe GNU troff output through command (which is read in copy
mode) by passing it to popen(3). Multiple pi requests
construct a multi-stage pipeline in the same order as the
formatter encounters the requests. Unsafe request; disabled
by default.
.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 unit v).
.pline Report, in JSON syntax to the standard error stream, the
list of output nodes corresponding to the pending output
line. In JSON, a pair of empty brackets "[ ]" represents an
empty list. A pending output line has not yet undergone
adjustment, and lacks a line number and margin character
(all as applicable).
.pm Report, to the standard error stream, the names of all
defined macros, strings, and diversions and their lengths in
characters or nodes.
.pm name ...
Report, to the standard error stream, the JSON-encoded name
and contents of each macro, string, or diversion name.
.pn +-N Set next page number.
.pnr Report the names, values, and (as applicable) autoincrement
amounts and assigned formats of all defined registers to the
standard error stream.
.pnr reg ...
Report the name and value and, if its type is numeric, the
autoincrement amount and assigned format, of each register
reg to the standard error stream.
.po Change to previous page offset. The current page offset is
available in register .o.
.po +-N Alter page offset (default scaling unit m).
.ps Restore previous type size.
.ps +-N Set/increase/decrease the type size to/by N scaled points (a
non-positive resulting type size is set to 1 u); also see
\s[+-N].
.psbb postscript-file
Retrieve the bounding box of the PostScript image found in
postscript-file, which must conform to Adobe's Document
Structuring Conventions (DSC). See registers llx, lly, urx,
ury.
.pso command
As "so", except that input comes from the standard output
stream of command, which is passed to popen(3). Unsafe
request; disabled by default.
.pstream Report, in JSON syntax to the standard error stream, the
list of open streams, including the name of each open
stream, the name of the file backing it, and its mode
(writing or appending).
.pwh 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 unit p).
.rchar c...
Remove definition of each ordinary, special, or indexed
character c, undoing the effect of a char, fchar, or schar
request. Spaces need not separate c arguments. The
character definition removed (if any) is the first
encountered in the resolution process documented in section
"Using Symbols" of Groff: The GNU Implementation of troff.
Glyphs, which are defined by font description files, cannot
be removed.
.rd Read insertion from standard input stream, ringing terminal
bell as prompt.
.rd terminal-message
Read insertion from standard input stream, writing
terminal-message to standard error stream as prompt.
.return Stop interpreting an interpolated macro, skipping the
remainder of its definition.
.return input
As return, but perform the skip twice--once within the macro
being interpreted and once in an enclosing macro.
.rfschar f c...
Remove each fallback special character c for font f. Spaces
need not separate c arguments. See fschar.
.rj Break, right-align the output of the next productive input
line without filling, then break again.
.rj npl Break, right-align the output of the next npl productive
input lines without filling, then break again. If npl <= 0,
stop right-aligning.
.rm name ...
Remove each 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 reg ...
Remove each register reg.
.rs Restore spacing; disable no-space mode. See .ns.
.rt Return (upward only) to vertical position marked by .mk on
the current page.
.rt N Return (upward only) to vertical position N (default scaling
unit v).
.schar c Define global fallback character c as empty.
.schar c contents
Define global fallback character c as contents. As char,
but GNU troff locates a character defined with schar after
any fonts named as arguments to the "special" request and
before any mounted special fonts.
.shc Reset the soft hyphen character to \[hy].
.shc c Set the soft hyphen character to c.
.shift Shift macro or string parameters one place n places:
argument i becomes argument i-1; argument 1 becomes
unavailable.
.shift n Shift macro or string parameters n places: argument i
becomes argument i-n; arguments 1 to n become unavailable.
.sizes s1 s2 ... sn [0]
Set available type sizes to the list of values or ranges;
each si is interpreted in units of scaled points (s). GNU
troff strips a leading neutral double quote from s1; it
reads each si in copy mode.
.so file Replace the request's control line with the contents of
file, "sourcing" it. GNU troff searches for file in any
directories specified by -I command-line options, followed
by the current working directory. If file does not exist,
the formatter ignores the request. (GNU troff emits a
warning in category "file".)
.soquiet file
As "so", but no warning is emitted if file does not exist.
.sp Break and move the next text baseline down by one vee, or
until springing a page location trap. If invoked with the
no-break control character, sp moves the text baseline
applicable to the entire pending output line.
.sp vertical-distance
As sp, but move by vertical-distance instead of 1v. Inside
a diversion, the formatter ignores any argument. A negative
vertical-distance cannot reduce the position of the text
baseline below zero. Applying the boundary-relative
measurement operator | operator to vertical-distance, as in
"|N", moves to a position relative to the page top for
positive N, and the bottom if N is negative.
.special Empty the list of special fonts designated by this request
when given arguments.
.special s ...
Declare each font s as special, irrespective of its
description file, populating a list that GNU troff searches,
in order, to find the glyph demanded. GNU troff searches
fonts specified as arguments to the "special" request after
those given as arguments to the fspecial request.
.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 adjusted output line is
greater than or equal to N. A negative N is treated as 0.
The default scaling unit is m. At startup, spreadwarn is
inactive and N is 3 m.
.ss n Set minimum inter-word space and supplemental inter-sentence
space sizes to n 12ths of the selected font's spacewidth
parameter (default: 12).
.ss n m As ".ss n", but set supplemental inter-sentence space size
to m 12ths of the selected font's spacewidth parameter.
.stringdown str
Replace each byte in the string named str with its lowercase
version.
.stringup str
Replace each byte in the string named str with its uppercase
version.
.sty pos style
Associate abstract style with non-negative font position
pos.
.substring str start [end]
Replace the string named str with its substring bounded by
the indices start and end, inclusive. Negative indices
count backward from the end of the string.
.sv As ne, but save 1 v for output with os request.
.sv d As ne, but save distance d for later output with os request
(default scaling unit v).
.sy command
Execute command (which is read in copy mode) in the
operating environment by passing it to system(3). See
register systat. Unsafe request; disabled by default.
.ta Clear tab stops.
.ta n1 n2 ... nn T r1 r2 ... rn
Set tabs at positions n1, n2, ..., nn, then set tabs at
nn+mxrn+r1 through nn+mxrn+rn, where m increments from 0, 1,
2, ... to the output line length. Each n argument can be
prefixed with a "+" to place the tab stop ni at a distance
relative to the previous, n(i-1). Each argument ni or ri
can be suffixed with a letter to align text within the tab
column bounded by tab stops i and i+1; "L" for left-aligned
(the default), "C" for centered, and "R" for right-aligned.
.tag Reserved for internal use.
.taga Reserved for internal use.
.tc Unset tab repetition character.
.tc c Set tab repetition character to c (default: none).
.ti +-N Temporarily indent next output line (default scaling
unit m).
.tkf font s1 n1 s2 n2
Enable track kerning for font.
.tl 'left'center'right'
Format three-part title.
.tm Write a newline to the standard error stream.
.tm terminal-message
Send terminal-message, followed by a newline, to the
standard error stream. The formatter reads the argument to
the end of the input line in copy mode, but does not remove
a leading double quote; contrast .tm1.
.tm1 As tm.
.tm1 message
As tm, but removes a leading neutral double quote `"' from
message, permitting initial embedded spaces in it, and reads
it to the end of the input line in copy mode.
.tmc No operation.
.tmc message
As tm1, but does not append a newline.
.tr abcd...
Translate ordinary or special characters a to b, c to d, and
so on prior to output.
.trf file Break and copy contents of file as "throughput" to GNU troff
output (see groff_out(5)). Unlike cf, characters invalid as
input to GNU troff are discarded. If file's contents do not
end with a newline, trf appends one.
.trin abcd...
As tr, except that asciify ignores the translation when a
diversion is interpolated.
.trnt abcd...
As tr, except that translations are suppressed in the
argument to \!.
.troff Make the conditional expressions t true and n false.
.uf font Set underline font used by ul to font.
.ul Underline (italicize in troff mode) the output of the next
productive input line.
.ul npl Underline (italicize in troff mode) the output of the next
npl productive input line. If npl=0, stop underlining.
.unformat div
Unformat space characters and tabs in diversion div,
preserving font information.
.vpt Enable vertical position traps. They are enabled by
default.
.vpt b Enable or disable vertical position traps per Boolean
expression b.
.vs Change to previous vertical spacing.
.vs +-N Set vertical spacing to +-N (default scaling unit p).
.warn Enable all warning categories.
.warn 0 Disable all warning categories.
.warn n Enable warnings in categories whose codes sum to n; see
troff(1).
.warnscale scaling-unit
Select scaling unit used in certain warnings (one of u, i,
c, p, or P; default: i). Ignored on nroff-mode output
devices, for which these diagnostics report the vertical
page location in lines, and the horizontal page location in
ens.
.wh vertical-position
Remove visible page location trap at vertical-position
(default scaling unit v).
.wh vertical-position mac
Plant macro mac as page location trap at vertical-position
(default scaling unit v), removing any visible trap already
there.
.while cond-expr
Interpolate newlines unless and until cond-expr evaluates
false.
.while cond-expr input
Repeatedly execute input unless and until cond-expr
evaluates false.
.write stream character-sequence
Write character-sequence, a sequence of ordinary characters,
spaces, or tabs, to stream, which must previously have been
the subject of an "open" (or opena) request, followed by a
newline. GNU troff flushes the stream after writing to it.
.writec stream character-sequence
As "write", but does not write a newline to the output.
.writem stream name
Write the contents of the macro or string name to stream,
which must previously have been the subject of an "open" (or
opena) request. GNU troff reads the contents of name in
copy mode.
Escape sequence short reference
The escape sequences \", \#, \$, \*, \?, \a, \e, \n, \t, \g, \V, and
\newline are interpreted even in copy mode.
The escape sequences \f, \F, \H, \m, \M, \R, \s, and \S are not
tokenized when GNU troff reads its input. \R updates only the
formatter's register dictionary, and does not contribute (directly) to
output. The others alter the environment (see section "Environments"
below). See the "GNU troff Internals" section of the groff Texinfo
manual.
\" Comment; read everything up to the next newline in copy mode and
discard it.
\# Whole-line comment; read everything up to and including the next
newline in copy mode and discard it.
\*s Interpolate string with one-character name s.
\*(st Interpolate string with two-character name st.
\*[string]
Interpolate string with name string (of arbitrary length).
\*[string arg ...]
Interpolate string with name string (of arbitrary length),
taking arg ... as arguments.
\$0 Interpolate name by which currently executing macro was invoked.
\$n Interpolate macro or string parameter numbered n (1<=n<=9).
\$(nn Interpolate macro or string parameter numbered nn (01<=nn<=99).
\$[nnn]
Interpolate macro or string parameter numbered nnn (nnn>=1).
\$* Interpolate catenation of all macro or string parameters,
separated by spaces.
\$@ Interpolate catenation of all macro or string parameters, with
each surrounded by double quotes and separated by spaces.
\$^ Interpolate catenation of all macro or string parameters as if
they were arguments to the ds request.
\' is a synonym for \[aa], the acute accent special character.
\` is a synonym for \[ga], the grave accent special character.
\- is a synonym for \[-], the minus sign special character.
\_ is a synonym for \[ul], the underrule special character.
\% Mark a hyphenation point within a word. At the beginning of a
word, prevent it from being otherwise hyphenated.
\!character-sequence
Transparently embed character-sequence, up to and including the
end of the line, into the current diversion, requests, macro
calls, and escape sequences when reading them into a diversion.
Doing so prevents them from taking effect until the diverted
text is actually output.
\?character-sequence\?
Transparently embed character-sequence, up to its own next
occurrence on the input line, into a diversion, or unformatted
as an output comparand in a conditional expression. Ignored in
the top-level diversion.
\space Move right one inter-word space.
\~ Insert an unbreakable, adjustable space.
\0 Move right by the width of a numeral in the current font.
\| Move one-sixth em to the right on typesetters.
\^ Move one-twelfth em to the right on typesetters.
\& Interpolate a dummy character.
\) Interpolate a dummy character that is transparent to end-of-
sentence recognition.
\/ Apply italic correction. Use between an immediately adjacent
oblique glyph on the left and an upright glyph on the right.
\, Apply left italic correction. Use between an immediately
adjacent upright glyph on the left and an oblique glyph on the
right.
\: Non-printing break point (similar to \%, but never produces a
hyphen glyph).
\newline
Continue current input line on the next.
\{ Begin conditional input.
\} End conditional input.
\(sc Interpolate glyph of special character with two-character
identifier sc.
\[spchar]
Interpolate glyph of special character with identifier spchar
(of arbitrary length).
\[base-char comp ...]
Interpolate composite glyph constructed from base-char and each
component comp.
\[charnnn]
Interpolate glyph of eight-bit encoded character nnn, where
0<=nnn<=255.
\[unnnn[n[n]]]
Interpolate glyph of Unicode character with code point
nnnn[n[n]] in uppercase hexadecimal.
\[ubase-char[_combining-component]...]
Interpolate composite glyph from Unicode character base-char
and combining-components.
\a Interpolate a leader in copy mode.
\A'input'
Interpolate 1 if input is a valid identifier, and 0 otherwise.
Because GNU troff ignores any input character with an invalid
code when reading it, invalid identifiers are empty or contain
spaces, tabs, newlines, or escape sequences that interpolate
something other than a sequence of ordinary characters.
\b'string'
Build bracket: pile a sequence of glyphs corresponding to each
character in string vertically, and center it vertically on the
output line.
\B'input'
Interpolate 1 if input is a valid numeric expression, and 0
otherwise.
\c Continue output line at next input line.
\C'glyph'
As \[glyph], but compatible with other troff implementations.
\d Move downward 1/2 em on typesetters.
\D'drawing-command'
See subsection "Drawing commands" below.
\e Interpolate the escape character.
\E As \e, but not interpreted in copy mode.
\fP Select previous font mounting position (abstract style or
font); same as ".ft" or ".ft P".
\fF Select font mounting position, abstract style, or font with
one-character name or one-digit position F. F cannot be P.
\f(ft Select font mounting position, abstract style, or font with
two-character name or two-digit position ft.
\f[font]
Select font mounting position, abstract style, or font with
arbitrarily long name or position font. font cannot be P.
\f[] Select previous font mounting position (abstract style or
font).
\Ff Set default font family to that with one-character name f.
\F(fm Set default font family to that with two-character name fm.
\F[fam] Set default font family to that with arbitrarily long name fam.
\F[] Set default font family to previous value.
\gr Interpolate format of register with one-character name r.
\g(rg Interpolate format of register with two-character name rg.
\g[reg] Interpolate format of register with arbitrarily long name reg.
\h'N' Horizontally move the drawing position by N ems (or specified
units); | may be used. Positive motion is rightward.
\H'N' Set (increment, decrement) the height of the current font, but
not its width. If N is zero, the formatter uses the font's
inherent height for its type size default scaling unit z).
\kr Store the horizontal drawing position, relative to that
corresponding to the start of the input line (ignoring page
offset and indentation), in register name r.
\k(rg Store the horizontal drawing position, relative to that
corresponding to the start of the input line (ignoring page
offset and indentation), in register name rg.
\k[reg] Store the horizontal drawing position, relative to that
corresponding to the start of the input line (ignoring page
offset and indentation), in register name reg.
\l'N[c]'
Draw horizontal line of length N with character c (default:
\[ru]; default scaling unit m).
\L'N[c]'
Draw vertical line of length N with character c (default:
\[br]; default scaling unit v).
\mc Select stroke color with one-character name c.
\m(cl Select stroke color with two-character name cl.
\m[color]
Select stroke color with arbitrarily long name color.
\m[] Restore previous stroke color.
\Mc Select fill color with one-character name c.
\M(cl Select fill color with two-character name cl.
\M[color]
Select fill color with arbitrarily long name color.
\M[] Restore previous fill color.
\nr Interpolate value of register with one-character name r.
\n(rg Interpolate value of register with two-character name rg.
\n[reg] Interpolate value of register with arbitrarily long name reg.
\N'n' Format indexed character numbered n in the current font.
\o'abc...'
Overstrike centered glyphs of characters a, b, c, and so on.
\O0 At the outermost suppression level, disable emission of glyphs
and geometric objects to the output driver.
\O1 At the outermost suppression level, enable emission of glyphs
and geometric objects to the output driver.
\O2 At the outermost suppression level, enable glyph and geometric
primitive emission to the output driver and write to the
standard error stream the page number, four bounding box
registers enclosing glyphs written since the previous \O escape
sequence, the page offset, line length, image file name (if
any), horizontal and vertical device motion quanta, and input
file name.
\O3 Begin a nested suppression level.
\O4 End a nested suppression level.
\O[5Pfile]
At the outermost suppression level, write the name file to the
standard error stream at position P, which must be one of l, r,
c, or i.
\p Break output line at next word boundary; adjust if applicable.
\r Move "in reverse" (upward) 1 em.
\R'name +-N'
Set, increment, or decrement register name by N.
\s+-N Set/increase/decrease the type size to/by N scaled points. N
must be a single digit. If n is an unsigned "0", restore the
previous size. (In compatibility mode only, a non-zero N must
be in the range 4-39.) Otherwise, as ps request.
\s(+-N
\s+-(N Set/increase/decrease the type size to/by N scaled points; N is
a two-digit number >=1. If n is an unsigned "00", restore the
previous size. Otherwise, as ps request.
\s[+-N]
\s+-[N]
\s'+-N'
\s+-'N' Set/increase/decrease the type size to/by N scaled points. If
n is an unsigned "0" (with any number of leading zeroes),
restore the previous size. Otherwise, as ps request.
\S'N' Slant the glyphs of the currently selected font by @var{N}
degrees. Positive values slant in the direction of text flow.
Only integer values are possible.
\t Interpolate a tab in copy mode.
\u Move upward 1/2 em on typesetters.
\v'N' Vertically move the drawing position by N vees (or specified
units); | may be used. Positive motion is downward.
\Ve Interpolate value of system environment variable with one-
character name e as returned by getenv(3).
\V(ev Interpolate value of system environment variable with two-
character name ev as returned by getenv(3).
\V[env] Interpolate value of system environment variable with
arbitrarily long name env as returned by getenv(3).
\w'input'
Interpolate the width of input, as interpreted, in basic units.
This escape sequence allows several properties of formatted
output to be measured without writing it out. The formatter
processes input in a dummy environment: this means that font
and type size changes, for example, may occur within it without
affecting subsequent output.
\x'N' Increase vertical spacing of pending output line by N vees (or
specified units; negative before, positive after).
\X'character-sequence'
Write character-sequence to troff output as a device extension
command. The groff special character repertoire is unknown to
output drivers outside of glyphs named in a device's fonts, and
even then they may not possess complete coverage of the names
documented in groff_char(7). Further, escape sequences that
produce horizontal or vertical motions, hyphenation breaks, or
that are dummy characters may appear in strings or be converted
to nodes, particularly in diversions. These are not
representable when interpolated directly into device-
independent output, as might be done when writing out tag names
for PDF bookmarks, which can appear in a viewer's navigation
pane.
So that documents or macro packages do not have to laboriously
"sanitize" strings destined for interpolation in device
extension commands, this escape sequence performs certain
transformations on its argument. For these transformations,
character translations and definitions are ignored.
GNU troff converts several ordinary characters that typeset as
non-basic Latin code points to code points outside that range
so that they are used consistently whether they are formatted
as glyphs or used in a device control command argument. These
ordinary characters are "'", "-", "^", "`", and "~"; others are
written as-is.
Special characters that typeset as Unicode basic Latin
characters are translated to basic Latin characters
accordingly. So that any Unicode code point can be represented
in device extension commands, for example in an author's name
in document metadata or as a usefully named bookmark or
hyperlink anchor, GNU troff maps other special characters to
Unicode special character notation. Special characters without
a Unicode representation, and escape sequences that do not
interpolate a sequence of ordinary and/or special characters,
produce warnings in category "char".
\Yn Write contents of macro or string n to troff output as a device
extension command.
\Y(nm Write contents of macro or string nm to troff output as a
device extension command.
\Y[name]
Write contents of macro or string name to troff output as a
device extension command.
\zc Format character c with zero width--without advancing the
drawing position.
\Z'input'
Save the drawing position, format input, then restore it. GNU
troff ignores tabs and leaders in input with an error
diagnostic.
Drawing commands
Drawing commands direct the output device to render geometrical objects
rather than glyphs. Specific devices may support only a subset, or may
feature additional ones; consult the man page for the output driver in
use. Terminals in particular implement almost none.
Rendering starts at the drawing position; when finished, the drawing
position is left at the rightmost point of the object, even for closed
figures, except where noted. GNU troff draws stroked (outlined)
objects with the stroke color, and shades filled ones with the fill
color. See section "Colors" above. Coordinates h and v are horizontal
and vertical motions relative to the drawing position or previous point
in the command. The default scaling unit for horizontal measurements
(and diameters of circles) is m; for vertical ones, v.
Circles, ellipses, and polygons can be drawn stroked or filled. These
are independent properties; if you want a filled, stroked figure, you
must draw the same figure twice using each drawing command. A filled
figure is always smaller than an outlined one because the former is
drawn only within its defined area, whereas strokes have a line
thickness (set with \D't').
\D'~ h1 v1 ... hn vn'
Draw B-spline to each point in sequence, leaving drawing
position at (hn, vn).
\D'a hc vc h v'
Draw circular arc centered at (hc, vc) counterclockwise from the
drawing position to a point (h, v) relative to the center.
(hc, vc) is adjusted to the point nearest the perpendicular
bisector of the arc's chord.
\D'c d'
Draw circle of diameter d with its leftmost point at the drawing
position.
\D'C d'
As \D'C', but the circle is filled.
\D'e h v'
Draw ellipse of width h and height v with its leftmost point at
the drawing position.
\D'E h v'
As \D'e', but the ellipse is filled.
\D'l h v'
Draw line from the drawing position to (h, v).
\D'p h1 v1 ... hn vn'
Draw polygon with vertices at the drawing position and each
point in sequence. GNU troff closes the polygon by drawing a
line from (hn, vn) back to the initial drawing position.
Afterward, the drawing position is left at (hn, vn).
\D'P h1 v1 ... hn vn'
As \D'p', but the polygon is filled.
\D't n'
Set stroke thickness of geometric objects to to n basic units.
A zero n selects the minimum supported thickness. A negative n
selects a thickness proportional to the type size; this is the
default.
Strings
groff supports strings primarily for user convenience. Conventionally,
if one would define a macro only to interpolate a small amount of text,
without invoking requests or calling any other macros, one defines a
string instead. Only one string is predefined by the language.
\*[.T] Contains the name of the output device (for example, "utf8"
or "pdf").
The ds request creates a string with a specified name and contents. If
the identifier named by ds already exists as an alias, the target of
the alias is redefined. If ds is invoked with only one argument, the
named string becomes empty. The formatter removes a leading neutral
double quote `"' from contents to permit the embedding of leading
spaces. It interprets any other `"' literally, but the wise author
uses the special character escape sequence \[dq] instead if the string
might be interpolated as part of a macro argument; see section "Calling
macros" above.
The \* escape sequence dereferences a string's name, interpolating its
contents. If the name does not exist, the formatter defines it as
empty, interpolates nothing, and emits a warning in category "mac".
See section "Warnings" in troff(1). The bracketed interpolation form
accepts arguments that are handled as macro arguments are; see section
"Calling macros" above. In contrast to macro calls, an argument
containing a closing bracket ] must be enclosed in double quotes. When
defining strings, argument interpolations must be escaped if they are
to reference parameters from the calling context; see section
"Parameters" below. Any non-initial neutral double quote " is
interpreted literally, but it is wise to use the special character
escape sequence \[dq] instead if the string might be interpolated as
part of a macro argument; see section "Calling macros" above. Strings
are not limited to a single input line of text. \newline works just as
it does elsewhere. The resulting string is stored without the
newlines. When filling is disabled, care is required to avoid
overrunning the line length when interpolating strings. Conversely,
when filling is enabled, it is not necessary to append \c to a string
interpolation to prevent a break afterward, as might be required in a
macro argument. Nor does a string require use of the GNU troff chop
request to excise a trailing newline as is often done with diversions.
It is not possible to embed a newline in a string that will be
interpreted as such when the string is interpolated. To achieve that
effect, use \* to interpolate a macro instead; see section "Punning
names" below.
The "as" request is similar to ds but appends to a string instead of
redefining it. If "as" is invoked with only one argument, no operation
is performed (beyond dereferencing the string).
Because strings are similar to macros, they too can be defined to
suppress AT&T troff compatibility mode enablement when interpolated;
see section "Compatibility mode" below. The ds1 request defines a
string that suspends compatibility mode when the string is later
interpolated. as1 is likewise similar to "as", with compatibility mode
suspended when the appended portion of the string is later
interpolated.
Caution: These requests treat the remainder of the input line as their
second argument, including any spaces, up to a newline or comment
escape sequence. Ending string definitions (and appendments) with a
comment, even an empty one, prevents unwanted space from creeping into
them during source document maintenance. This rule and suggestion also
applies to the second argument of the "length" request, to requests
that define characters (char, fchar, fschar, and schar), and to the
file name or command arguments of the cf, hpf, hpfa, mso, msoquiet, nx,
"open", opena, pi, pso, "so", soquiet, and trf requests.
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).
Redefinitions and appendments "write through" request, macro, string,
and diversion names. To replace an aliased object with a separately
defined one, you must use the rm request on its name first.
Registers
In the roff language, numbers and measurements can be stored in
registers. Many built-in registers exist, supplying anything from
components of the date to details of formatting parameters; some of
these are read-only. You can also define your own. See section
"Identifiers" above regarding the construction of valid names for
registers.
Each register (except read-only ones) can be assigned a format, causing
its value to interpolate with leading zeroes, in Roman numerals, or
alphabetically. Some read-only registers are string-valued, meaning
that they interpolate text and lack a format.
Define registers and update their values with the nr request or the \R
escape sequence.
User-defined registers can also be incremented or decremented by a
configured amount at the time they are interpolated. The value of the
increment is specified with a third argument to the nr request, and a
special interpolation syntax, \n+-, alters and then retrieves the
register's value. Together, these features are called auto-increment.
(A negative auto-increment can be considered an "auto-decrement".)
Many predefined registers are available. The following presentation
uses register interpolation syntax \n[name] to refer to a register name
to clearly distinguish it from a string or request name; the symbols
\n[] are not part of the register name. The register name space is
separate from that used for requests, macros, strings, and diversions.
Read-only registers
Predefined registers whose identifiers start with a dot are read-only.
Many are Boolean-valued.
Caution: Built-in registers are subject to removal like others; once
removed, they can be recreated only as normal writable registers and
will not otherwise reflect the configuration of the formatter.
A register name is often associated with a request of the same name
(without the dot); exceptions are noted.
\n[.$] Count of arguments passed to currently interpolated
macro or string.
\n[.a] Amount of extra post-vertical line space; see \x.
\n[.A] Approximate output is being formatted (Boolean-valued);
see troff -a option.
\n[.b] Font emboldening offset; see bd.
\n[.br] The normal control character was used to call the macro
being interpreted (Boolean-valued).
\n[.c] Input line number; see lf and register "c.".
\n[.C] AT&T troff compatibility mode is enabled (Boolean-
valued); see cp. Always false when processing "do"; see
register .cp.
\n[.cdp] Depth of last glyph formatted in the environment;
positive if glyph extends below the baseline.
\n[.ce] Count of input lines remaining to be centered in the
environment.
\n[.cht] Height of last glyph formatted in the environment;
positive if glyph extends above the baseline.
\n[.color] Color output is enabled (Boolean-valued).
\n[.cp] Within "do", the saved value of compatibility mode; see
register .C.
\n[.csk] Skew of the last glyph formatted in the environment; see
register skw.
\n[.d] Vertical drawing position in diversion.
\n[.ev] Name of environment (string-valued).
\n[.f] Mounting position of selected font; see ft and \f.
\n[.F] Name of input file (string-valued); see lf.
\n[.fam] Name of the environment's default font family (string-
valued).
\n[.fn] Resolved name of font selected in the environment
(string-valued); see ft and \f.
\n[.fp] Next non-zero free font mounting position index.
\n[.g] Always true in GNU troff (Boolean-valued).
\n[.h] Text baseline high-water mark on page or in diversion.
\n[.H] Horizontal motion quantum of output device in basic
units.
\n[.height] Height of the environment's selected font; see \H.
\n[.hla] Hyphenation language in environment (string-valued).
\n[.hlc] Count of immediately preceding consecutive hyphenated
lines in environment.
\n[.hlm] Maximum quantity of consecutive hyphenated lines allowed
in environment.
\n[.hy] Automatic hyphenation mode in environment.
\n[.hydefault] Hyphenation mode default in environment.
\n[.hym] Hyphenation margin in environment.
\n[.hys] Hyphenation space adjustment threshold in environment.
\n[.i] Environment's indentation amount; see "in".
\n[.in] Indentation amount applicable to the output line pending
in the environment; see ti.
\n[.int] The text most recently formatted in the environment was
"interrupted" or continued with \c (Boolean-valued).
\n[.it] Count of input lines remaining in the environment's
pending input trap.
\n[.itc] The environment's pending input trap honors output line
continuation with \c (Boolean-valued).
\n[.itm] Name of the macro associated with the pending input trap
(string-valued).
\n[.j] The environment's adjustment mode encoded as an integer;
see ad and na. Do not interpret or perform arithmetic
on its value.
\n[.k] The environment's horizontal drawing position relative
to indentation.
\n[.kern] Pairwise kerning is enabled (Boolean-valued).
\n[.l] Line length; see ll.
\n[.L] Line spacing; see ls.
\n[.lg] Ligature mode.
\n[.linetabs] Line-tabs mode is enabled in the environment (Boolean-
valued).
\n[.ll] Line length applicable to the environment's pending
output line.
\n[.lt] Environment's title line length.
\n[.m] Stroke color (string-valued); see gcolor and \m. The
default stroke color is named "default".
\n[.M] Fill color (string-valued); see fcolor and \M. The
default fill color is named "default".
\n[.n] Length of formatted output on previous output line.
\n[.ne] Amount of vertical space required by last ne that caused
a trap to be sprung; also see register .trunc.
\n[.nm] Output line numbering is enabled in the environment
(Boolean-valued).
\n[.nn] Count of lines remaining in the environment for which
numbering is suppressed while output line numbering is
enabled.
\n[.ns] No-space mode is enabled (Boolean-valued).
\n[.o] Page offset; see po.
\n[.O] Output suppression nesting level; see \O.
\n[.p] Page length; see pl.
\n[.P] The page is selected for output (Boolean-valued); see
troff -o option.
\n[.pe] Page ejection is in progress (Boolean-valued).
\n[.pn] Number of the next page.
\n[.ps] The environment's type size in scaled points.
\n[.psr] The environment's most recently requested type size in
scaled points; see ps and \s.
\n[.pvs] The environment's post-vertical line spacing.
\n[.R] Maximum representable integer in GNU troff.
\n[.rj] Count of input lines remaining to be right-aligned in
the environment.
\n[.s] The environment's type size in points as a decimal
fraction (string-valued); see ps and \s.
\n[.S] Reserved. Plan 9 troff uses this name for roughly the
same purpose as GNU troff's \n[.tabs]
\n[.slant] Slant in degrees of the environment's selected font; see
\S.
\n[.sr] The environment's most recently requested type size in
points as a decimal fraction (string-valued); see ps and
\s.
\n[.ss] Size of the environment's minimum inter-word space in
twelfths of the space width of the selected font.
\n[.sss] Size of the environment's supplemental inter-sentence
space in twelfths of the space width of the selected
font.
\n[.sty] The environment's selected abstract style (string-
valued); see ft and \f.
\n[.t] Distance to next vertical position trap; see wh and ch.
If no such traps exist between the drawing position and
the bottom of the page, troff interpolates the distance
to the page bottom. Within a diversion, in the absence
of a diversion trap, this distance is the maximum
possible vertical position supported by the output
device.
\n[.T] An output device was explicitly selected (Boolean-
valued); see troff -T option.
\n[.tabs] The environment's tab stop settings (if any) suitable
for use as argument to ta (string-valued).
\n[.trap] Name of the next vertical position trap after the
vertical drawing position. (string-valued); see wh, ch,
and dt.
\n[.trunc] Amount of vertical space truncated by the most recently
sprung vertical position trap, or, if the trap was
sprung by an ne, minus the amount of vertical motion
produced by ne; also see register .ne.
\n[.u] Filling is enabled in the environment (Boolean-valued);
see fi and nf.
\n[.U] Unsafe mode is enabled (Boolean-valued); see troff -U
option.
\n[.v] The environment's vertical line spacing; see vs.
\n[.V] Vertical motion quantum of the output device in basic
units.
\n[.vpt] Vertical position traps are enabled (Boolean-valued).
\n[.w] Width of last glyph formatted in the environment.
\n[.warn] Sum of the numeric codes of enabled warning categories.
\n[.x] Major version number of the running troff formatter.
\n[.y] Minor version number of the running troff formatter.
\n[.Y] Revision number of the running troff formatter.
\n[.z] Name of diversion (string-valued). Empty if output is
directed to the top-level diversion.
\n[.zoom] Magnification of the environment's selected font (in
thousandths; zero if no magnification); see fzoom.
Writable predefined registers
Several registers are predefined but also modifiable; some are updated
upon interpretation of certain requests or escape sequences. Date- and
time-related registers are set to the local time as determined by
localtime(3) when the formatter launches. This initialization can be
overridden by SOURCE_DATE_EPOCH and TZ; see section "Environment" of
groff(7).
\n[$$] Process ID of troff.
\n[%] Page number.
\n[c.] Input line number.
\n[ct] Union of character types of each glyph rendered into
dummy environment by \w.
\n[dl] Width of last closed diversion.
\n[dn] Height of last closed diversion.
\n[dw] Day of the week (1-7; 1 is Sunday).
\n[dy] Day of the month (1-31).
\n[hours] Count of hours elapsed since midnight (0-23).
\n[hp] Horizontal drawing position relative to that at the
start of the input line.
\n[llx] Lower-left x coordinate (in PostScript units) of
PostScript image; see psbb.
\n[lly] Lower-left y coordinate (in PostScript units) of
PostScript image; see psbb.
\n[ln] Output line number; see nm.
\n[lsn] Count of leading spaces on input line.
\n[lss] Amount of horizontal space corresponding to leading
spaces on input line.
\n[minutes] Count of minutes elapsed in the hour (0-59).
\n[mo] Month of the year (1-12).
\n[nl] Vertical drawing position.
\n[opmaxx]
\n[opmaxy]
\n[opminx]
\n[opminy] These four registers mark the top left- and bottom
right-hand corners of a rectangle encompassing all
formatted output on the page. They are reset to -1 by
\O0 or \O1.
\n[rsb] As register sb, adding maximum glyph height to
measurement.
\n[rst] As register st, adding maximum glyph depth to
measurement.
\n[sb] Maximum displacement of text baseline below its original
position after rendering into dummy environment by \w.
\n[seconds] Count of seconds elapsed in the minute (0-60).
\n[skw] Skew of last glyph rendered into dummy environment by
\w.
\n[slimit] The maximum depth of troff's internal input stack. If
<=0, there is no limit: recursion can continue until
available memory is exhausted. The default is 1,000.
\n[ssc] Subscript correction of last glyph rendered into dummy
environment by \w.
\n[st] Maximum displacement of text baseline above its original
position after rendering into dummy environment by \w.
\n[systat] Return value of system(3); see sy.
\n[urx] Upper-right x coordinate (in PostScript units) of
PostScript image; see psbb.
\n[ury] Upper-right y coordinate (in PostScript units) of
PostScript image; see psbb.
\n[year] Gregorian year.
\n[yr] Gregorian year minus 1900.
Using fonts
In digital typography, a font is a collection of characters in a
specific typeface that a device can render as glyphs at a desired size.
(Terminals and some typesetters have fonts that render at only one or
two sizes. As examples, take the groff lj4 device's Lineprinter, and
lbp's Courier and Elite faces.) A roff formatter can change typefaces
at any point in the text. The basic faces are a set of styles
combining upright and slanted shapes with normal and heavy stroke
weights: "R", "I", "B", and "BI"--these stand for roman, bold, italic,
and bold-italic. For linguistic text, GNU troff groups typefaces into
families containing each of these styles. (Font designers prepare
families such that the styles share esthetic properties.) A text font
is thus often a family combined with a style, but it need not be:
consider the ps and pdf devices' ZCMI (Zapf Chancery Medium
italic)--often, no other style of Zapf Chancery Medium is provided. On
typesetters, at least one special font is available, comprising
unstyled glyphs for mathematical operators and other purposes.
Like the AT&T troff formatter, GNU troff does not itself load or
manipulate a digital font file; instead it works with a font
description file that characterizes it, including its glyph repertoire
and the metrics (dimensions) of each glyph. This information permits
the formatter to accurately place glyphs with respect to each other.
Before using a font description, the formatter associates it with a
mounting position, a place in an ordered list of available typefaces.
So that a document need not be strongly coupled to a specific font
family, in GNU troff an output device can associate a style in the
abstract sense with a mounting position. Thus the default family can
be combined with a style dynamically, producing a resolved font name.
A user-specified font name that combines family and style, or refers to
a font that is not a member of a family, is already "resolved".
Fonts often have trademarked names, and even Free Software fonts can
require renaming upon modification. groff maintains a convention that
a device's serif font family is given the name T ("Times"), its sans-
serif family H ("Helvetica"), and its monospaced family C ("Courier").
Historical inertia has driven groff's font identifiers to short
uppercase abbreviations of font names, as with TR, TB, TI, TBI, and a
special font S.
The default family used with abstract styles can be changed at any
time; initially, it is T. Typically, abstract styles are arranged in
the first four mounting positions in the order shown above. The
default mounting position, and therefore style, is always 1 (R). By
issuing appropriate formatter instructions, you can override these
defaults before your document writes its first glyph.
Terminals cannot change font families and lack special fonts. They
support style changes by overstriking, or by altering ISO 6429/ECMA-48
graphic renditions (character cell attributes).
The ft request and \f escape sequence select a typeface by name,
abstract style, or mounting position. The fam request and \F escape
sequence set the default font family. The ftr request translates one
font name to another; fzoom magnifies or reduces the typeface
corresponding to a resolved one. sty and fp associate abstract styles
and font names with mounting positions.
Characters and glyphs
A glyph is a graphical representation of a character. Whereas a
character is an abstraction of semantic information, a glyph is an
intelligible mark visible on screen or paper. A character has many
possible representation forms; for example, the character "A" can be
written in an upright or slanted typeface, producing distinct glyphs.
Sometimes, a sequence of characters map to a single glyph:@: this is a
ligature--the most common is `fi'.
Space characters never become glyphs in GNU troff. If not discarded
(as when trailing text lines), horizontal motions represent them in the
output.
The formatter supports three kinds of character. An ordinary character
(see section "Identifiers" above) is the most commonly used, has no
special syntax, and typically represents itself. (Depending on the
breadth of the output device's glyph repertoire, the characters ', -,
^, `, and ~ can be exceptions to this rule. " and \ are not
exceptions, but because they are syntactically meaningful to the
formatter, access to their glyphs may require use of special characters
(or changing or disabling the escape character). See groff_char(7).
Interpolate a special character with the "\[xxx] or "\C'xxx'" escape
sequence syntax, where xxx is an identifier. An indexed character
bypasses most character-to-glyph resolution logic, uses the
"\N'i'syntax, and selects a glyph from the currently selected font by
its integer-valued position i in the output device's representation of
that font. (A device's fonts do not necessarily arrange their glyphs
according to a standard character encoding.)
User-defined characters are similar to string definitions (see section
"Strings" above) and permit extension of or substitution within the
character repertoire. Any ordinary, special, or indexed character can
be user-defined. The char, fchar, schar, and fschar requests create
user-defined characters employed at various stages of the character-to-
glyph resolution process.
In a troff system, a font description file lists all of the glyphs a
particular font provides. If the user requests a glyph not available
in the currently selected font, the formatter looks it up an ordered
list of special fonts. By default, the "ps" (PostScript) and "pdf"
output devices support the two special fonts "SS" (slanted symbol) and
"S" (symbol); and these devices' DESC files arrange them such that the
formatter searches the former before the latter. Other output devices
use different names for special fonts. Fonts mounted with the fonts
keyword in the DESC file are globally available. GNU troff's special
and fspecial requests alter the list of fonts treated as special on a
general basis, or only when a certain font is currently selected,
respectively.
GNU troff employs the following procedure to resolve an input character
into a glyph. User-defined characters make this resolution process
recursive. The first step that succeeds ends the resolution procedure
for the character being formatted, which may not be the last in the
sequence interpolated by a user-defined character.
o Interpolate the definition of any character defined by the char
request and apply this procedure to each character in its
definition.
o Check the current font for a glyph corresponding to the
character.
o Interpolate the definition of any user-defined character
matching defined by the fchar request and apply this procedure
to each character in its definition.
o Check whether the current font has a font-specific list of
special fonts; if so, check the each font therein, in the order
determined by the last applicable fspecial request, for a glyph
corresponding to the character.
o Interpolate the definition of any character defined by the
fschar request for the currently selected font, and apply this
procedure to each character in its definition.
o Check each font in the list configured by the most recently
issued special request for a glyph corresponding to the
character.
o Interpolate the definition of any character defined by the
sschar request and apply this procedure to each character in its
definition.
o Finally, iterate through the list of mounted fonts by position.
For each mounted font, if that font bears the special directive
(see groff_font(5)), check it for a glyph corresponding to the
character. This stage of the resolution process can sometimes
lead to surprising results since the fonts directive in the DESC
file often contains empty positions that are filled by a macro
file or document employing the fp request after the formatter
initializes.
Special fonts
Special fonts are those that the formatter searches, in mounting
position order, when it cannot find a requested glyph in the selected
font. Typically, they are declared as such in their description files
(see groff_font(5)), and contain unstyled glyphs. The "Symbol" and
"Zapf Dingbats" fonts of the PostScript and PDF standards are examples.
Ordinarily, only typesetters have special fonts.
GNU troff's special and fspecial requests permit a document to
supplement the set of fonts the device configures for glyph search
without having to use the fp request to manipulate the list of mounting
positions, which can be tedious--by default, GNU troff mounts 40 fonts
at startup when using the ps device.
Hyphenation
When filling, groff hyphenates words as needed at user-specified and
automatically determined hyphenation points. Explicitly hyphenated
words such as "mother-in-law" are always eligible for breaking after
each of their hyphens. The hyphenation character \% and non-printing
break point \: escape sequences may be used to control the hyphenation
and breaking of individual words. The hw request sets user-defined
hyphenation points for specified words at any subsequent occurrence.
Otherwise, groff determines hyphenation points automatically by
default.
Several requests influence automatic hyphenation. Because conventions
vary, a variety of hyphenation modes is available to the hy request;
these determine whether hyphenation will apply to a word prior to
breaking a line at the end of a page (more or less; see below for
details), and at which positions within that word automatically
determined hyphenation points are permissible. The localization macro
files loaded by troffrc configure a default hyphenation mode
appropriate to the language.
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 or column, even
for explicitly hyphenated words. (Hyphenation is prevented if
the next page location trap is closer to the vertical drawing
position than the next text baseline would be. See section
"Traps" below.)
4 disables hyphenation before the last two characters of a word.
8 disables hyphenation after the first two characters of a word.
16 enables hyphenation before the last character of a word.
32 enables hyphenation after the first character of a word.
Apart from value 2, restrictions imposed by the hyphenation mode are
not respected for words whose hyphenations have been specified with the
hyphenation character ("\%" by default) or the .hw request.
Nonzero values are additive. For example, mode 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 non-zero 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 due to a limit on consecutive hyphenated
lines (hlm), a minimum line length threshold (hym), or because the line
can instead be adjusted with additional inter-word space (hys).
Localization
GNU troff ties the set of hyphenation patterns to the hyphenation
language code selected by the hla request. The hpf request is usually
invoked by a localization file loaded by the troffrc file. groff
provides localization files for several languages; See subsection
"Localization packages" of groff_tmac(5). For Western languages, the
localization file sets the default hyphenation mode and loads
hyphenation patterns and exceptions. By default, troffrc loads the
localization file for English.
Writing macros
The .de request defines a macro named for its argument. If that name
already exists as an alias, the target of the alias is redefined; see
section "Strings" above. troff enters "copy mode" (see below), storing
subsequent input lines as the definition. If the optional second
argument is not specified, the definition ends with the control line
".." (two dots). Tabs and spaces are permitted between the dots.
Alternatively, a second argument to .de names a macro whose call (or
request whose invocation) syntax ends the definition; this end macro is
then interpreted normally. Spaces or tabs are permitted after the
first control character in the line containing this ending token, but a
tab immediately after the token prevents its recognition as the end of
a macro definition. Macro definitions can be nested if they use
distinct end macros or if their ending tokens are sufficiently escaped.
An end macro need not be defined until it is called. This fact enables
a nested macro definition to begin inside one macro and end inside
another.
Variants of .de disable compatibility mode and/or indirect the names of
the macros specified for definition or termination: these are .de1,
.dei, and .dei1. Append to macro definitions with .am, .am1, .ami, and
.ami1. The .als, .rm, and .rn requests create an alias of, remove, and
rename a macro, respectively. .return stops the execution of a macro
immediately, returning to the enclosing context.
Parameters
Macro call and string interpolation parameters can be accessed using
escape sequences starting with "\$". The \n[.$] read-only register
stores the count of parameters available to a macro or string; change
its value with the .shift request, which dequeues parameters from the
current list. The \$0 escape sequence interpolates the name by which a
macro was called. Applying string interpolation to a macro does not
change this name.
Copy mode
GNU troff processes certain requests in copy mode: it copies ordinary,
special, and indexed characters as-is; interpolates the escape
sequences \n, \g, \$, \*, \V, and \? normally; discards comments \" and
\#; interpolates \a, \e, and \t, as the current leader, escape, or tab
character with respectively; represents \newline, \&, \_, \|, \^, \{,
\}, \`, \', \-, \!, \c, \%, \space, \E, \), \~, and \: in an encoded
form, and copies other escape sequences as-is. The term "copy mode"
reflects its most visible application in requests that populate macros
and strings, but other requests also use it when interpreting arguments
that can't meaningfully represent typesetting operations. For example,
a font selection escape sequence has no meaning in a hyphenation
pattern file name (hpf) or a diagnostic message written to the terminal
(tm). The complement of copy mode--a roff formatter's behavior when
not defining or appending to a macro, string, or diversion--where all
macros are interpolated, requests invoked, and valid escape sequences
processed immediately upon recognition, can be termed interpretation
mode.
The escape character (\ by default) when used before itself quotes an
escape character for later interpretation in an enclosing context.
Escape character quotation enables you to control whether the formatter
interprets a given \n, \g, \$, \*, \V, or \? escape sequence at the
time the macro containing it is defined, or later when the macro is
called.
You can think of \\ as a "delayed" backslash; it is the escape
character followed by a backslash from which the escape character has
removed its special meaning. Consequently, \\ is not best considered
an escape sequence, but a quoted escape character. In any escape
sequence \X that troff does not recognize, the formatter discards the
escape character and outputs X. An unrecognized escape sequence causes
a warning in category "escape", with two exceptions, \\ being one. The
other is \., which quotes the control character. It is used to permit
nested macro definitions to end without a named macro call to conclude
them. Without a syntax for quoting the control character, this would
not be possible. Outside of copy mode, roff documents should not use
the \\ or \. character sequences; they serve only to obfuscate the
input. Use \e to represent the escape character, \[rs] to obtain a
backslash glyph, and \& before . and ' where troff expects them as
control characters if you mean to use them literally.
Macro definitions can be nested to arbitrary depth. Given the input
character sequence "\\" in a macro or string definition, the formatter
interprets each escape character in multiple contexts; once, when
populating the macro or string, where the first "\" serves its
quotation function--thus only one "\" is stored in the definition.
(Verify this fact with the pm request.) The formatter interprets the
second "\" as an escape character (assuming the escape character hasn't
been changed in the meantime) each time it interpolates the macro or
string definition. This fact leads to exponential growth in the
quantity of escape characters required to quote and thereby delay
interpolation of \n, \g, \$, \*, \V, and \? at each nesting level. An
alternative is to use \E, which represents an escape character that is
not interpreted in copy mode. Because \. is not a true escape
sequence, we can't use \E to keep ".." from ending a macro definition
prematurely. If the multiplicity of backslashes complicates
maintenance, use end macros.
Traps
Traps are locations in the output, or conditions on the input that,
when reached or fulfilled, call a specified macro. A vertical position
trap calls a macro when the formatter's vertical drawing position
reaches or passes, in the downward direction, a certain location on the
output page or in a diversion. Its applications include setting page
headers and footers, body text in multiple columns, and footnotes.
These traps can occur at a given location either on the page (wh, ch)
or in the current diversion (dt)--together, these are known as vertical
position traps, which can be disabled and renabled (vpt).
A diversion is not formatted in the context of a page, so it lacks page
location traps; instead it can have a diversion trap. There can exist
at most one such vertical position trap per diversion.
Other kinds of trap can be planted at a blank line (blm); at a line
with leading space characters (lsm); after a certain number of
productive input lines (it, itc); or at the end of input (em).
Setting a trap is also called planting one. It is said that a trap is
sprung if its condition is fulfilled.
The formatter passes no arguments to macros called by traps.
Registers associated with trap management include vertical position
trap enablement status (\n[.vpt]), distance to the next trap (\n[.t]),
and the name of that trap (\n[.trap]); the count of lines remaining in
the pending input trap (\n[.it]), the name of the macro associated with
it (\n[.itm]), and whether that input trap honors the \c output line
continuation escape sequence (\n[.itc]); 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]).
Page location traps
A page location trap is a vertical position trap that applies to the
page; that is, to the top-level diversion. Many can be present; manage
them with the wh and ch requests. Non-negative page locations given to
these requests set the trap relative to the top of the page; negative
values set the trap relative to the bottom of the page. It is not
possible to plant a trap less than one basic unit from the page bottom:
a location of "-0" is interpreted as "0", the top of the page. An
existing visible trap (see below) at the same location is removed; this
is wh's sole function if its second argument is missing.
A trap is sprung only if it is visible, meaning that its location is
reachable on the page and it is not hidden by another trap at the same
location already planted there. (A trap planted at "20i" or "-30i"
will not be sprung on a page of length "11i".)
A trap above the top or at or below the bottom of the page can be made
visible by either moving it into the page area or increasing the page
length so that the trap is on the page. A negative trap value always
uses the current page length; the formatter does not convert it to an
absolute vertical position. We can use the pwh request to dump page
location traps to the standard error stream; see section "Debugging"
below. GNU troff reports their positions in basic units, and includes
empty slots in the list, where a trap had been planted but subsequently
(re)moved, because they can affect the visibility of subsequently
planted traps.
The implicit page trap
An implicit page trap always exists in the top-level diversion (see
below); its purpose is to eject the current page and start the next
one. It works like a trap in some ways but not others. It has no
name, so it cannot be moved or deleted with wh or ch requests. You
cannot hide it by placing another trap at its location, and can move it
only by redefining the page length with pl. Its operation is
suppressed when vertical page traps are disabled with GNU troff's vpt
request.
Diversions
In roff systems it is possible to format text as if for output, but
instead of writing it immediately, one can divert the formatted text
into a named storage area. It is retrieved later by specifying its
name after a control character. The formatter uses the same name space
for such diversions as for strings and macros; see section
"Identifiers" above. Such text is sometimes said to be "stored in a
macro", but this coinage obscures the important distinction between
macros and strings on one hand and diversions on the other; the former
store unformatted input text, and the latter capture formatted output.
Diversions also do not interpret arguments. Applications of diversions
include footnotes, tables of contents, indices, and "keeps" (preventing
a page break from occurring at an inconvenient place by forcing a set
of output lines to be set as a group). For orthogonality it is said
that GNU troff populates the top-level diversion if no diversion is
active (that is, formatted output is being "diverted" directly to the
output device). The top-level diversion has no name.
Dereferencing an undefined diversion creates an empty one of that name.
(GNU troff also emits a warning in category "mac"; see section
"Warnings" of troff(1).) A diversion does not exist for the purpose of
testing with the d conditional expression operator until its initial
definition ends; see subsection "Conditional expressions" above.
The di request creates a diversion, including any partially collected
line. da appends to a diversion, creating one if it does not already
exist. If the diversion's name already exists as an alias, the target
of the alias is replaced or appended to; see section "Strings" above.
The pending output line is diverted as well. Switching to another
environment (with the ev request) before invoking di or da avoids
including any pending output line in the diversion. (See section
"Environments[" below.)
Invoking di or da without an argument stops diverting output to the
diversion named by the most recent corresponding request. Invoking di
or da without an argument when no diversion is being populated does
nothing. (GNU troff emits a warning in category "di"; see section
"Warnings" of troff(1).)
box and boxa work similarly, but ignore partially collected lines.
Call any of these macros again without an argument to end the
diversion.
Diversion requests can be nested. The registers .d and .z report
information about the current diversion, and dn and dl about the most
recently closed one. .h is meaningful in diversions, including the
top-level one.
After output to a (named) diversion stops, the formatter stores its
vertical and horizontal sizes, to the writable registers dn and dl,
respectively. Only the lines just processed are counted: for the
computation of dn and dl, the requests da and boxa are handled as if di
and box had been used, respectively--lines that have been already
stored in the diversion (box) are not taken into account.
The \! and \? escape sequences and output request escape from a
diversion, the first two to the enclosing level and the last to the top
level. This facility is termed transparent embedding.
The asciify and "unformat" requests reprocess diversions.
Punning names
Macros, strings, and diversions share a name space; see section
"Identifiers" above. Internally, the same mechanism is used to store
them. You can thus call a macro with string interpolation syntax and
vice versa. Interpolating a string does not hide existing macro
arguments. Place the sequence \\ at the end of a line in a macro
definition or, within a macro definition, immediately after the
interpolation of a macro as a string, to suppress the effect of a
newline.
Environments
Environments store most of the parameters that control text processing.
A default environment named "0" (zero) exists when exists when the
formatter starts up; formatting-related requests and escape sequences
modify its properties.
You can create new environments and switch among them. Only one is
current at any given time. Active environments are managed using a
stack, a data structure supporting "push" and "pop" operations. The
current environment is at the top of the stack. The same environment
name can be pushed onto the stack multiple times, possibly interleaved
with others. Popping the environment stack does not destroy the
current environment; it remains accessible by name and can be made
current again by pushing it at any time. Environments cannot be
renamed or deleted, and can only be modified when current. To inspect
the environment stack, use the pev request; see section "Debugging"
below.
Environments store the following information.
o a partially collected line, if any
o data about the most recently output glyph and line (registers .cdp,
.cht, .csk, .n, .w)
o typeface parameters (size, family, style, height and slant, inter-
word and inter-sentence space sizes)
o page parameters (line length, title length, vertical spacing, line
spacing, indentation, line numbering, centering, right-alignment,
underlining, hyphenation parameters)
o filling enablement; adjustment enablement and mode
o tab stops; tab, leader, escape, control, no-break control,
hyphenation, and margin characters
o input line traps
o stroke and fill colors
The ev request (with an argument) pushes to and (without) pops from the
environment stack, while evc copies a named environment's parameters to
the current one.
Postprocessor access
Beyond the cf and trf requests, two escape sequences and two requests
enable documents to pass information directly to a postprocessor.
These are useful for exercising device-specific capabilities that the
groff language does not abstract or generalize; examples include the
embedding of hyperlinks and image files. Device-specific functions are
documented in each output driver's man page, such as gropdf(1),
grops(1), or grotty(1).
The "device" request and \X escape sequence embed their arguments into
GNU troff output as parameters to an "x X" device extension command
(see groff_out(5)). The interpretation of such parameters is
determined by the output driver or other postprocessor.
GNU troff also permits the interpolation of macro or string contents as
a device extension command. The devicem request and \Y escape sequence
correspond to ".device \*[name]" and "\X'\*[name]", respectively. They
differ from their counterparts in that GNU troff does not interpret the
contents of the string or macro name; further, name may be a macro and
thus contain newlines. (There is no way to embed a newline in the
arguments to "device" or \X.) The inclusion of newlines requires an
extension to the AT&T troff device-independent page description
language, and their presence confuses drivers that do not know about it
(see subsection "Device control commands" of groff_out(5)).
Use of device extension commands early in a document (before the first
text is formatted) can interfere with processing of page location
traps. If you experience problems when placing them early, precede the
first with a dummy character escape sequence "\&"; recall section
"Dummy Characters" above.
The tag and taga requests are reserved for internal use.
Underlining
In RUNOFF (see roff(7)), underlining, even of lengthy passages, was
straightforward because only fixed-pitch printing devices were
targeted. Typesetter output posed a greater challenge. There exists a
groff request .ul (see above) that underlines subsequent source lines
on terminals, but on typesetters, it selects an italic font style
instead. The ms macro package (see groff_ms(7)) offers a macro .UL,
but it too produces the desired effect only on typesetters, and has
other limitations.
One could adapt ms's approach to the construction of a macro as
follows.
.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
selection escape sequence 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 in after
Underlining by overstriking with \(ul
The \z escape sequence writes a glyph without advancing the drawing
position, enabling overstriking. Thus, \zc\(ul formats c with an
underrule glyph on top of it. Video terminals implement the underrule
by setting a character cell's underline attribute, so this technique
works in both nroff and troff modes.
Long words may then look intimidating in the input; a clarifying
approach might be to use the input line continuation escape sequence
\newline to place each underlined character on its own input line.
Thus,
.nf
\&\fB: ${\fIvar\fR\c
\zo\(ul\
\zp\(ul\c
\&\fIvalue\fB}
.fi
produces
: ${var__value}
as output.
Compatibility mode
groff_diff(7) documents differences between the roff language
recognized by GNU troff and that of AT&T troff, as well as the device,
font, and device-independent page description formats described by
CSTR #54. GNU troff provides an AT&T troff compatibility mode. The cp
request and registers .C and .cp set and test the enablement of this
mode.
Debugging
Preprocessors use the lf request to preserve the identities of line
numbers and names of input files. groff emits a variety of error
diagnostics and supports several categories of warning; the output of
these can be selectively suppressed with "warn" (and see the -E, -w,
and -W options of troff(1)). A trace of the formatter's input
processing stack can be emitted when errors or warnings occur by means
of troff(1)'s -b option, or produced on demand with the backtrace
request. 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. Examine
the state of the formatter with requests that write lists of defined
names--macros, strings, and diversions--(pm); characters (pchar;
experimental); colors (pcolor); composite character mappings
(pcomposite); environments (pev); occupied font mounting positions
(pfp); font translations (pftr); automatic hyphenation codes (pchar)
and exceptions (phw); registers (pnr); open streams (pstream); and page
location traps (pwh). Requests can also disclose to the standard error
stream the internal properties and representations of characters and
classes (pchar), macros (and strings and diversions) (pm), and the list
of output nodes corresponding to the pending input line (pline).
Authors
This document was written by Trent A. Fisher, Werner Lemberg <wl@gnu
.org>, and G. Branden Robinson <g.branden.robinson@gmail.com>. Section
"Underlining" was primarily written by Bernd Warken <groff-bernd
.warken-72@web.de>.
See also
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 Technical
Report No. 54, widely called simply "CSTR #54", documents the language,
device and font description file formats, and device-independent page
description language 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 Technical Report No. 97 (CSTR #97),
provides additional insights into the device and font description file
formats and device-independent page description language.
groff(7)
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 the man pages
provided with the GNU roff system.
groff_char(7)
discusses character encoding issues and escape sequences that
produce glyphs.
groff_diff(7)
covers differences between the GNU troff formatter, its device
and font description file formats, its device-independent page
description language, and those of AT&T troff.
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.
roff(7)
presents a detailed history of roff systems and summarizes
concepts common to them.
groff 1.24.1 2026-05-15 groff(7)
groff 1.24.1 - Generated Mon May 18 16:44:00 CDT 2026