|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
groff(7) Miscellaneous Information Manual groff(7)
groff - GNU roff language reference
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, DVI, and PDF, may
be available in /usr/local/share/doc/groff-1.23.0.
groff is also a name for an extended dialect of the roff
language. We use “roff” to denote features that are universal,
or nearly so, among implementations of this family. 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.
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 text
input files, and translates that input into a device-independent
output format (groff_out(5)) that is usually then post-processed
by an output driver to produce PostScript, PDF, HTML, DVI, or
terminal output.
Input to GNU troff is organized into lines separated by the Unix
newline character (U+000A), and must be in one of two character
encodings it can recognize: IBM code page 1047 on EBCDIC systems,
and ISO Latin-1 (8859-1) otherwise. Use of ISO 646-1991:IRV
(“US-ASCII”) or (equivalently) the “Basic Latin” subset of
ISO 10646 (“Unicode”) is recommended; see groff_char(7). The
preconv(1) preprocessor transforms other encodings, including
UTF-8, to satisfy troff's requirements.
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, .cf, .fi, .fl, .in, .nf,
.rj, .sp, .ti, and .trf requests. The requested operation
takes effect at the next break. It makes .br 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. In the .ds, .ds1, .as, and
.as1 requests, a leading neutral double quote in the second
argument is stripped off to allow embedding of leading
spaces. 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.
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.
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 in the middle of a
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 is incremented.
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 contains a
positive value if the last output line was continued with \c;
this datum is associated with the environment.
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.)
Numeric parameters that specify measurements are expressed as
integers or decimal fractions with an optional scaling unit
suffixed. A scaling unit is a letter that immediately follows
the last digit of a number. Digits after the decimal point are
optional.
Measurements are scaled by the scaling unit and stored 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. The only constraint on the basic unit is that it
is at least as small as any other unit.
u Basic 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.
s, z Scaled points and multiplication by the output device's
sizescale parameter, respectively.
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; an en is one-half em.
v Vee; distance between text baselines.
M Hundredth of an em.
Motion quanta
An output device's basic unit u is not necessarily its smallest
addressable length; u can be smaller to avoid problems with
integer roundoff. 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.
Measurements are rounded 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
should also be kept in mind; see below.
A numeric expression evaluates to an integer. The following
operators are recognized.
+ 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 motion
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 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. Overflow and
division (or 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 extrema of two operands: >? (maximum) and <?
(minimum).
Comparison operators comprise < (less than), > (greater than), <=
(less than or equal), >= (greater than or equal), and = (equal).
== is a synonym for =. When evaluated, a comparison is replaced
with “0” if it is false and “1” if true. In the roff language,
positive values are true, others false.
We can 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, ! is recognized only at
the beginning of a numeric expression not contained by another
numeric expression. In other words, it must be the “outermost”
operator. Including it elsewhere in the expression produces a
warning in the “number” category (see troff(1)), and its
expression evaluates false. This unfortunate limitation
maintains compatibility with AT&T troff. Test a numeric
expression for falsity 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, 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 \B escape sequence 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.
Due to the way arguments are parsed, spaces are not allowed in
numeric expressions unless the (sub)expression containing them is
surrounded by parentheses.
An identifier labels a GNU troff datum such as a register, name
(macro, string, or diversion), typeface, color, special character
or character class, environment, or stream. Valid identifiers
consist of one or more ordinary characters. An ordinary
character is an input character that is not the escape character,
a leader, tab, newline, or invalid as GNU troff input.
Invalid input characters are a subset of control characters (from
the sets “C0 Controls” and “C1 Controls” as Unicode describes
them). When troff encounters one in an identifier, it produces a
warning in category “input” (see section “Warnings” in troff(1)).
They are removed during interpretation: an identifier “foo”,
followed by an invalid character and then “bar”, is processed as
“foobar”.
On a machine using the ISO 646, 8859, or 10646 character
encodings, invalid input characters are 0x00, 0x0B, 0x0D–0x1F,
and 0x80–0x9F. On an EBCDIC host, they are 0x00–0x01, 0x08,
0x09, 0x0B, 0x0D–0x14, 0x17–0x1F, and 0x30–0x3F. Some of these
code points are used by troff internally, making it non-trivial
to extend the program to accept UTF-8 or other encodings that use
characters from these ranges.
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.
If you begin a macro, string, or diversion name with either of
the characters “[” or “]”, you foreclose use of the refer(1)
preprocessor, which recognizes “.[” and “.]” as bibliographic
reference delimiters.
The escape sequence \A tests its argument for validity as an
identifier.
How GNU troff handles the interpretation of an undefined
identifier depends on the context. 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, troff emits a warning in category “mac”, defines it as
empty, and interpolates nothing. If the identifier is
interpreted as a register, troff emits a warning in category
“reg”, initializes it to zero, and interpolates that value. See
section “Warnings” in troff(1), and subsection “Interpolating
registers” and section “Strings” below. Attempting to use an
undefined typeface, style, special character or character class,
color, environment, 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 are recognized 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; use 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.
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.
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.
If a macro of the desired name does not exist when called, it is
created, assigned an empty definition, and a warning in category
“mac” is emitted. 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.
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 a newline.
If an escape character is followed by a character that does not
identify a defined operation, the escape character is ignored
(producing a diagnostic of the “escape” warning category, which
is not enabled by default) and the following character is
processed normally.
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).
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.
Letters, numerals, and leaders can be used. Punctuation
characters are likely better choices, except for those defined as
infix operators in numeric expressions; see below.
The following escape sequences don't take arguments and thus are
allowed as delimiters: \space, \%, \|, \^, \{, \}, \', \`, \-,
\_, \!, \?, \), \/, \,, \&, \:, \~, \0, \a, \c, \d, \e, \E, \p,
\r, \t, and \u. However, using them this way is discouraged;
they can make the input confusing to read.
A few escape sequences, \A, \b, \o, \w, \X, and \Z, accept a
newline as a delimiter. Newlines that serve as delimiters
continue to be recognized as input line terminators. Use of
newlines as delimiters in escape sequences is also discouraged.
Finally, the escape sequences \D, \h, \H, \l, \L, \N, \R, \s, \S,
\v, and \x prohibit many delimiters.
• the numerals 0–9 and the decimal point “.”
• the (single-character) operators +-/*%<>=&:()
• any escape sequences other than \%, \:, \{, \}, \', \`,
\-, \_, \!, \/, \c, \e, and \p
Delimiter syntax is complex and flexible primarily for historical
reasons; the foregoing restrictions need be kept in mind mainly
when using groff in AT&T compatibility mode. 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 any that result
from interpolation. Typically, ' works fine. See section
“Implementation differences” in groff_diff(7).
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.
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, anything, 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 anything are
therefore not seen. anything effectively cannot be omitted; if
cond-expr is true and anything is empty, the newline at the end
of the control line is interpreted as a blank line (and therefore
a blank text line).
It is frequently desirable for a control structure to govern more
than one request, 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.
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 glyph g is available.
d m a string, macro, diversion, or request m is
defined.
e the current page number is even.
F f a font named f is available.
m c a color named c is defined.
n the formatter is in nroff mode.
o the current page number is odd.
r n a register named n is defined.
S s a font style named s is available.
t the formatter is in troff mode.
v n/a (historical artifact; always false).
If the first argument to an .if, .ie, or .while request begins
with a non-alphanumeric character apart from ! (see below); it
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. troff formats s1 and s2 in separate scratch
buffers; after the comparison, the resulting data are discarded.
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 comparands
protected with \? are read in copy mode, they need not even be
valid groff syntax. 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.
In the following request and escape sequence specifications, most
argument names were chosen to be descriptive. A few denotations
may require introduction.
anything includes all characters up to the end of the
input line (which may be continued with
\newline), to the ending delimiter for the
escape sequence, or within \{ and \}. Escape
sequences in anything are interpreted normally
except where otherwise stated, as when read in
copy mode. Comments are ignored; trailing
whitespace generally is not.
b is a numerical expression evaluated as a
Boolean; positive values are true, others
false.
c denotes a single input character, ordinary or
special.
div is a diversion identifier.
env is an environment identifier.
font is a typeface specified as a font name, 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 a character sequence to be emitted on the
standard error stream. Special character
escape sequences are not interpreted.
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 or escape
sequences like \D. Macro calls are not
themselves productive, but their interpolated
contents 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 leading minus
sign in N is always interpreted as a decrementation operator, not
an algebraic sign. To assign a register a negative value or the
negated value of another register, enclose it with its operand in
parentheses or subtract it from zero. If a prior value does not
exist (the register was undefined), an increment or decrement is
applied as if to 0.
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 processing; exit with failure status.
.ab message
Abort processing; write 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 old
Create alias (additional name) new for existing
register named old.
.als new old
Create alias (additional name) new for existing
request, string, macro, or diversion old. If new
already exists, its contents are lost unless already
aliased.
.am mac Append to macro mac until encountering “..”.
.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 anything
Append anything to string str.
.as1 ident As “.as ident”.
.as1 str anything
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.
.backtrace Write the state of the input stack to the standard
error stream. See the -b option of groff(1).
.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.
.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 output line; adjust if applicable.
.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 Copy contents of file without formatting to the (top-
level) diversion.
.cflags n c1 c2 ...
Assign properties encoded by n to characters c1, c2,
and so on.
.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 Remove definition of ordinary or special character c.
.char c contents
Define ordinary or special character c as anything. A
leading neutral double quote in the second argument is
stripped from it, allowing embedded leading spaces in
contents, which is read in copy mode and continues to
the end of the input line.
.chop name Remove the last character from the macro, string, or
diversion name.
.class ident c1 c2 ...
Define a (character) class ident comprising the
characters or range expressions c1, c2, and so on.
.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 c1 c2
Map ordinary or special character c1 to c2 when c1 is
a combining component in a composite character.
.continue Finish the current iteration of a .while loop.
.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 font n m
Set constant character width mode for font to n/36 ems
with em m.
.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 contents
Write contents, read in copy mode, to troff output as
a device control command. A leading neutral double
quote is stripped to allow embedding of leading
spaces.
.devicem name
Write contents of macro or string name to troff output
as a device control command.
.di Stop directing output to current diversion.
.di ident Direct output to diversion ident.
.do name ...
Interpret the string, request, diversion, or macro
name (along with any arguments) with compatibility
mode disabled. Compatibility mode is restored (only
if it was active) when the expansion of name is
interpreted.
.ds ident Create empty string named ident.
.ds ident contents
Create a string named ident containing contents. A
leading neutral double quote in the second argument is
stripped from it, allowing embedded leading spaces in
contents, which is read in copy mode and continues to
the end of the input line.
.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 anything
Interpret anything as if it were an input line if the
conditional expression of the corresponding .ie
request was false.
.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 with successful status.
.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 Remove definition of fallback character c.
.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.
.fcolor Restore previous fill color.
.fcolor color
Select color 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
Remove definition of fallback character c specific to
font f.
.fschar f c contents
Define fallback character c specific to font f as
contents. As char, but a character defined by fschar
is located after the list of fonts declared with
fspecial is searched and before those declared with
the “special” request.
.fspecial font
Empty the list of fonts treated as special when font
is selected.
.fspecial font s1 s2 ...
When font is selected, treat the fonts s1, s2, ... as
special.
.ft
.ft P Select previous font mounting position (abstract style
or font); same as \f[] or \fP.
.ft font Select typeface font, a mounting position, abstract
style, or font name; same as \f[font] escape sequence.
font cannot be P.
.ftr f Remove translation of font named f.
.ftr f1 f2 Translate font name f1 to f2.
.fzoom font
.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.
.gcolor color
Select color as the stroke color.
.hc Reset the hyphenation character to \% (the default).
.hc c Change the hyphenation character to c.
.hcode c1 code1 [c2 code2] ...
Set the hyphenation code of character c1 to code1,
that of c2 to code2, and so on.
.hla Clear hyphenation language (disabling automatic
hyphenation).
.hla ident Set the hyphenation language to ident.
.hlm Set the consecutive automatically hyphenated line
limit to -1, meaning “no limit”.
.hlm n Set the consecutive automatically hyphenated line
limit to to n. A negative value means “no limit”.
.hpf pattern-file
Read hyphenation patterns from pattern-file.
.hpfa pattern-file
Append hyphenation patterns from pattern-file.
.hpfcode a b [c d] ...
Define mappings for character codes in hyphenation
pattern files read with .hpf and .hpfa.
.hw word ...
Define hyphenation overrides for each word; a hyphen
“-” 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 the line can be justified with the addition
of up to hyphenation-space to each inter-word space
(default scaling unit m).
.ie cond-expr anything
If cond-expr is true, interpret anything as if it were
an input line, otherwise skip to a corresponding .el
request.
.if cond-expr anything
If cond-expr is true, then interpret anything as if it
were an input line.
.ig Ignore 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, except that input lines interrupted with the
\c escape sequence are not counted.
.kern Enable pairwise kerning.
.kern n If n is zero, disable pairwise kerning, otherwise
enable it.
.lc Unset leader repetition character.
.lc c Set leader repetition character to c (default: “.”).
.length reg anything
Compute the number of characters of anything 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 n Set number of next input line to n.
.lf n file Set number of next input line to n and input file name
to file.
.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.
.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 file is sought in the tmac
directories.
.msoquiet file
As .mso, but no warning is emitted if file does not
exist.
.na Disable output line adjustment.
.ne 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, 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 to be
numbered with nm.
.nn n Suppress numbering of the next n output lines to be
numbered with nm. If n=0, cancel suppression.
.nop anything
Interpret anything 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.
.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 append to file. Unsafe request;
disabled by default.
.os Output vertical distance that was saved by the .sv
request.
.output contents
Emit contents directly to troff's output. A leading
neutral double quote in the argument is stripped,
allowing embedded leading spaces in contents, which is
read in copy mode and continues to the end of the
input line.
.pc Reset page number character to ‘%’.
.pc c Change the page number character used in titles to c.
.pcolor Report, to the standard error stream, the list of
defined color names. A device's default stroke and/or
fill colors, “default”, are not listed since they are
immutable and their details unknown to the formatter.
.pcomposite
Report, to the standard error stream, the list of
defined composite characters. 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.
.phw Report, to the standard error stream, the list of
hyphenation exceptions. Each hyphenation point is
marked with “-”. Words that will not be hyphenated at
all are prefixed with “-”. Those to which the
automatic hyphenation mode applies (meaning those
defined in a hyphenation pattern file rather than with
the hw request) are suffixed with a tab and asterisk
(*).
.pi program
Pipe output to program (nroff only). 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, to the standard error stream, the list of
output nodes corresponding to the pending output line.
The list is empty if there are none.
.pm Report, to the standard error stream, the names and
sizes in bytes of defined macros, strings, and
diversions.
.pn ±N Set next page number.
.pnr Report the names and contents of all defined registers
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 file Retrieve the bounding box of the PostScript image
found in file, which must conform to Adobe's Document
Structuring Conventions (DSC). See registers llx,
lly, urx, ury.
.pso command-line
Execute command-line with popen(3) and interpolate its
output. Unsafe request; disabled by default.
.ptr Report names and positions of all page location traps
to the standard error stream.
.pvs Change to previous post-vertical line spacing.
.pvs ±N Change post-vertical line spacing according to ±N
(default scaling unit p).
.rchar c1 c2 ...
Remove definition of each ordinary or special
character c1, c2, ... defined by a .char, .fchar, or
.schar request.
.rd prompt Read insertion.
.return Stop interpreting an interpolated macro, skipping the
remainder of its definition.
.return anything
As return, but perform the skip twice—once within the
macro being interpreted and once in an enclosing
macro.
.rfschar f c1 c2 ...
Remove the font-specific definitions of glyphs c1, c2,
... for font f.
.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 Remove definition of global fallback character c.
.schar c contents
Define global fallback character c as contents. As
char, but a character defined with schar is located
after the list of fonts declared with 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 n In a macro definition, left-shift arguments by
n positions.
.sizes s1 s2 ... sn [0]
Set available type sizes similarly to the sizes
directive in a DESC file. Each si is interpreted in
units of scaled points (z).
.so file Replace the request's control line with the contents
of file, “sourcing” it.
.soquiet file
As .so, but no warning is emitted if file does not
exist.
.sp Break and move the next text baseline down by one vee,
or until springing a page location trap.
.sp dist Break and move the next text baseline down by dist, or
until springing a page location trap (default scaling
unit v). A negative dist will not reduce the position
of the text baseline below zero. Prefixing dist with
the | operator moves to a position relative to the
page top for positive N, and the bottom if N is
negative; in all cases, one line height (vee) is added
to dist. dist is ignored inside a diversion.
.special Reset global list of fallback special fonts to be
empty.
.special s1 s2 ...
Fonts s1, s2, etc. are special and are searched for
glyphs not in the current font.
.spreadwarn
Toggle the spread warning on and off (the default)
without changing its value.
.spreadwarn N
Emit a break warning if the additional space inserted
for each space between words in an 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 additional inter-
sentence space sizes to n 12ths of the selected font's
spacewidth parameter (default: 12).
.ss n m As “.ss n”, but set additional inter-sentence space
size to n 12ths of the selected font's spacewidth
parameter.
.stringdown stringvar
Replace each byte in the string named stringvar with
its lowercase version.
.stringup stringvar
Replace each byte in the string named stringvar with
its uppercase version.
.sty 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 backwards 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-line
Execute command-line with system(3). Unsafe request;
disabled by default.
.ta n1 n2 ... nn T r1 r2 ... rn
Set tabs at positions n1, n2, ..., nn, then set tabs
at nn+m×rn+r1 through nn+m×rn+rn, where m increments
from 0, 1, 2, ... to the output line length. Each
n argument can be prefixed with a “+” to place the tab
stop ni at a distance relative to the previous,
n(i-1). Each argument ni or ri can be suffixed with a
letter to align text within the tab column bounded by
tab stops i and i+1; “L” for left-aligned (the
default), “C” for centered, and “R” for right-aligned.
.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 message
Write message, followed by a newline, to the standard
error stream.
.tm1 message
As .tm, but recognizes and strips a leading neutral
double quote, allowing embedded leading spaces in
message.
.tmc message
As .tm1, without emitting a newline.
.tr abcd...
Translate ordinary or special characters a to b, c to
d, and so on prior to output.
.trf file Transparently output the contents of file. Unlike
.cf, invalid input characters in file are rejected.
.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 in nroff mode.
.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 anything
Repeatedly execute anything unless and until cond-expr
evaluates false.
.write stream contents
Write contents to stream, which must previously have
been the subject of an .open request, followed by a
newline. A leading neutral double quote in the second
argument is stripped, allowing embedded leading spaces
in contents, which is read in copy mode until the end
of the line.
.writec stream contents
As .write, but does not append a newline to contents.
.writem stream name
Write contents of macro or string name to stream.
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 groff reads its input; \R updates only the
formatter's internal state, and the rest only the environment.
They do not contribute (directly) to output; see the “Gtroff
Internals” section of the groff Texinfo manual.
\" Comment; ignore everything up to the next newline.
\# Comment; ignore everything up to and including the next
newline.
\*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 concatenation of all macro or string
parameters, separated by spaces.
\$@ Interpolate concatenation of all macro or string
parameters, with each surrounded by double quotes and
separated by spaces.
\$^ Interpolate concatenation of all macro or string
parameters as if they were arguments to the .ds request.
\' 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.
\% Control hyphenation.
\! Transparent line. The remainder of the input line is
interpreted (1) when the current diversion is read; or (2)
if in the top-level diversion, by the postprocessor (if
any).
\?anything\?
Transparently embed anything, read in copy mode, in 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.
\(gl Interpolate glyph with two-character name gl.
\[glyph]
Interpolate glyph with name glyph (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'anything'
Interpolate 1 if anything is a valid identifier, and 0
otherwise.
\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'anything'
Interpolate 1 if anything is a valid numeric expression,
and 0 otherwise.
\c Continue output line at next input line.
\C'glyph'
As \[glyph], but compatible with other troff
implementations.
\d Move downward ½ 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 height of current font to N scaled points (or
specified units).
\kr Mark horizontal position in one-character register name r.
\k(rg Mark horizontal position in two-character register
name rg.
\k[reg]
Mark horizontal position in register with arbitrarily long
name reg.
\l'N[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 Set stroke color to that with one-character name c.
\m(cl Set stroke color to that with two-character name cl.
\m[color]
Set stroke color to that with arbitrarily long name color.
\m[] Restore previous stroke color.
\Mc Set fill color to that with one-character name c.
\M(cl Set fill color to that with two-character name cl.
\M[color]
Set fill color to that with arbitrarily long name color.
\M[] Restore previous fill color.
\nr Interpolate contents of register with one-character
name r.
\n(rg Interpolate contents of register with two-character
name rg.
\n[reg]
Interpolate contents of register with arbitrarily long
name reg.
\N'n' Interpolate glyph with index 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; 0 restores the previous type
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. As .ps request.
\s[±N]
\s±[N]
\s'±N'
\s±'N' Set/increase/decrease the type size to/by N scaled points.
As .ps request.
\S'N' Slant output glyphs by N degrees; the direction of text
flow is positive.
\t Interpolate a tab in copy mode.
\u Move upward ½ 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 contents of environment variable with one-
character name e.
\V(ev Interpolate contents of environment variable with two-
character name ev.
\V[env]
Interpolate contents of environment variable with
arbitrarily long name env.
\w'anything'
Interpolate width of anything, formatted in a dummy
environment.
\x'N' Increase vertical spacing of pending output line by N vees
(or specified units; negative before, positive after).
\X'contents'
Write contents to troff output as a device control
command. Within anything, the escape sequences \&, \),
\%, and \: are ignored; \space and \~ are converted to
single space characters; and \\ has its escape character
stripped. So that the basic Latin subset of the Unicode
character set can be reliably encoded in anything, the
special character escape sequences \-, \[aq], \[dq],
\[ga], \[ha], \[rs], and \[ti] are mapped to basic Latin
characters; see groff_char(7). For this transformation,
character translations and special character definitions
are ignored.
\Yn Write contents of macro or string n to troff output as a
device control command.
\Y(nm Write contents of macro or string nm to troff output as a
device control command.
\Y[name]
Write contents of macro or string name to troff output as
a device control command.
\zc Format character c with zero width—without advancing the
drawing position.
\Z'anything'
Save the drawing position, format anything, then restore
it.
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 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 minimal supported thickness.
A negative n selects a thickness proportional to the type
size; this is the default.
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 called
with only one argument, the named string becomes empty.
Otherwise, troff stores the remainder of the control line in copy
mode; see subsection “Copy mode” below.
The \* escape sequence dereferences a string's name,
interpolating its contents. If the name does not exist, it is
defined as empty, nothing is interpolated, and a warning in
category “mac” is emitted. 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, however, if a closing bracket
] occurs in a string argument, that argument 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.
The formatter removes a leading neutral double quote " in the
string contents to permit the embedding of leading spaces. Any
other " 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.
The .as request is similar to .ds but appends to a string instead
of redefining it. If .as is called with only one argument, no
operation is performed (beyond dereferencing 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: The ds request, unlike others, treats the remainder of
the input line as its second argument, including trailing spaces.
Ending string definitions (and appendments) with a comment, even
an empty one, prevents unwanted space from creeping into them
during source document maintenance.
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.
In the roff language, numbers can be stored in registers. Many
built-in registers exist, supplying anything from the date to
details of formatting parameters. You can also define your own.
See section “Identifiers” above for information on constructing a
valid name for a register.
Define registers and update their values with the nr request or
the \R escape sequence.
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±, is used to alter and
then retrieve 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. In the following
presentation, the register interpolation syntax \n[name] is used
to refer to a register name to clearly distinguish it from a
string or request name. The register name space is separate from
that used for requests, macros, strings, and diversions. Bear in
mind that the symbols \n[] are not part of the register name.
Read-only registers
Predefined registers whose identifiers start with a dot are read-
only. Many are Boolean-valued. Some are string-valued, meaning
that they interpolate text. A register name (without the dot) is
often associated with a request of the same name; 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
currently interpolated macro (Boolean-valued).
\n[.c] Input line number; see .lf and register “c.”.
\n[.C] 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 output lines remaining to be centered.
\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 default font family (string-valued).
\n[.fn]
Resolved name of selected font (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]
Font height; 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] Indentation amount; see .in.
\n[.in]
Indentation amount applicable to the pending output line;
see .ti.
\n[.int]
Previous output line was “interrupted” or continued with
\c (Boolean-valued).
\n[.it]
The count of lines remaining in the pending input trap.
\n[.itc]
The pending input trap honors output line continuation \c
(Boolean-valued).
\n[.itm]
Name of the macro associated with the pending input trap
(string-valued).
\n[.j] Adjustment mode encoded as an integer; see .ad and .na.
Do not interpret or perform arithmetic on its value.
\n[.k] 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 (Boolean-valued).
\n[.ll]
Line length applicable to the pending output line.
\n[.lt]
Title 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 (Boolean-valued).
\n[.nn]
Count of output lines remaining to have numbering
suppressed.
\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]
Type size in scaled points.
\n[.psr]
Most recently requested type size in scaled points; see
.ps and \s.
\n[.pvs]
Post-vertical line spacing.
\n[.R] Count of available unused registers; always 10,000 in GNU
troff.
\n[.rj]
Count of lines remaining to be right-aligned.
\n[.s] Type size in points as a decimal fraction (string-valued);
see .ps and \s.
\n[.slant]
Slant of font in degrees; see \S.
\n[.sr]
Most recently requested type size in points as a decimal
fraction (string-valued); see .ps and \s.
\n[.ss]
Size of minimal inter-word space in twelfths of the space
width of the selected font.
\n[.sss]
Size of additional inter-sentence space in twelfths of the
space width of the selected font.
\n[.sty]
Selected abstract style (string-valued); see .ft and \f.
\n[.t] Distance to next vertical position trap; see .wh and .ch.
\n[.T] An output device was explicitly selected (Boolean-valued);
see troff -T option.
\n[.tabs]
Representation of tab settings suitable for use as
argument to .ta (string-valued).
\n[.trap]
Name of the next vertical position trap that will be
sprung (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 (Boolean-valued); see .fi and .nf.
\n[.U] Unsafe mode is enabled (Boolean-valued); see troff -U
option.
\n[.v] 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]
Zoom multiplier of current 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(1).
\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.
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 a resolved
one. sty and fp associate abstract styles and font names with
mounting positions.
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.
(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).
The set of hyphenation patterns is associated with the
hyphenation language set by the .hla request. The .hpf request
is usually invoked by a localization file loaded by the troffrc
file. groff provides localization files for several languages;
see groff_tmac(5). These also set the default automatic
hyphenation mode with .hydefault.
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
troff processes certain requests in copy mode: it interpolates
the escape sequences \n, \g, \$, \*, \V, and \? normally;
interprets \newline immediately; discards comments \" and \#;
interpolates the current leader, escape, or tab character with
\a, \e, and \t, respectively; and represents all other escape
sequences in an encoded form. 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, can escape itself. This
enables you to control whether a given \n, \g, \$, \*, \V, or \?
escape sequence is interpreted at the time the macro containing
it is defined, or later when the macro is called.
You can think of \\ as a “delayed” backslash; it is the escape
character followed by a backslash from which the escape character
has removed its special meaning. Consequently, \\ is not an
escape sequence in the usual sense. In any escape sequence \X
that troff does not recognize, the escape character is ignored
and X is output. An unrecognized escape sequence causes a
warning in category “escape”, with two exceptions, \\ being one.
The other is \., which escapes the control character. It is used
to permit nested macro definitions to end without a named macro
call to conclude them. Without a syntax for escaping the control
character, this would not be possible. roff documents should not
use the \\ or \. character sequences outside of copy mode; 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. In “\\”,
each escape character is interpreted twice—once in copy mode,
when the macro is defined, and once in interpretation mode, when
the macro is called. This fact leads to exponential growth in
the quantity of escape characters required to 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 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 on the page (.wh, .ch); at a
given location in the current diversion (.dt)—together, these are
known as vertical position traps, which can be disabled and re-
enabled (.vpt).
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). Macros called by traps are passed no arguments. Setting
a trap is also called planting one. It is said that a trap is
sprung if its condition is fulfilled.
Registers associated with trap management include vertical
position trap enablement status (\n[.vpt]), distance to the next
trap (\n[.t]), amount of needed (.ne-requested) space that caused
the most recent vertical position trap to be sprung (\n[.ne]),
amount of needed space truncated from the amount requested
(\n[.trunc]), page ejection status (\n[.pe]), and leading space
count (\n[lsn]) with its corresponding amount of motion
(\n[lss]).
Page location traps
A page location trap is a vertical position trap that applies to
the page; that is, to undiverted output. 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. Negative trap
values always use the current page length; they are not converted
to an absolute vertical position. Use .ptr to dump page location
traps to the standard error stream; their positions are reported
in basic units.
The implicit page trap
An implicit page trap always exists in the top-level diversion
(see below); it works like a trap in some ways but not others.
Its purpose is to eject the current page and start the next one.
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 the vpt request.
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 same name
space is used 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 “keeps”
(preventing a page break from occurring at an inconvenient place
by forcing a set of output lines to be set as a group),
footnotes, tables of contents, and indices. For orthogonality it
is said that GNU troff is in the top-level diversion if no
diversion is active (that is, formatted output is being
“diverted” immediately to the output device. The top-level
diversion has no name.
Dereferencing an undefined diversion will create an empty one of
that name and cause a warning in category mac to be emitted.
(see section “Warnings” in troff(1)). A diversion does not exist
for the purpose of testing with the d conditional 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. 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, .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 completing a diversion, the writable registers dn and dl
contain its vertical and horizontal sizes, 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.
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. The sequence \\ can be placed 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 store most of the parameters that control text
processing. A default environment named “0” exists when troff
starts up; it is modified by formatting-related requests and
escape sequences.
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.
• a partially collected line, if any
• data about the most recently output glyph and line (registers
.cdp, .cht, .csk, .n, .w)
• typeface parameters (size, family, style, height and slant,
inter-word and inter-sentence space sizes)
• page parameters (line length, title length, vertical spacing,
line spacing, indentation, line numbering, centering, right-
alignment, underlining, hyphenation parameters)
• filling enablement; adjustment enablement and mode
• tab stops; tab, leader, escape, control, no-break control,
hyphenation, and margin characters
• input line traps
• stroke and fill colors
The ev request pushes to and pops from the environment stack,
while evc copies a named environment's contents to the current
one.
Two escape sequences and two requests enable documents to pass
information directly to an output driver or other 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 control
command (see groff_out(5)). The interpretation of such
parameters is determined by the output driver or other
postprocessor.
Within a device control command, the escape sequences \&, \), \%,
and \: are ignored; \space and \~ are converted to single space
characters; and a self-escaped escape character is output as a
backslash \. So that the basic Latin subset of the Unicode
character set (that is, ISO 646:1991-IRV or, popularly, “US-
ASCII”) can be reliably encoded in device control commands, seven
special character escape sequences (“\-”, “\[aq]”, “\[dq]”,
“\[ga]”, “\[ha]”, “\[rs]”, and “\[ti]”) are mapped to basic Latin
characters; see groff_char(7). For this transformation,
character translations and special character definitions are
ignored. (They are bypassed because these parameters are not
rendered as glyphs in the output; instead, they remain abstract
characters—in a PDF bookmark or a URL, for example.)
Escape sequences other than the foregoing in device control
command may be ignored, or produce an error.
A device control command issued with the “device” request will
not be reflected in the output unless a partially collected line
exists at least once in the top-level diversion (recall section
“Diversions” above). When experimenting with such device
controls in minimal documents, a br request will ensure this to
be the case.
If the use_charnames_in_special directive appears in the output
device's DESC file, the use of special character escape sequences
is not an error; they are simply output verbatim (with the
exception of the seven mapped to Unicode basic Latin characters,
discussed above). use_charnames_in_special is currently employed
only by grohtml(1).
GNU troff also permits the interpolation of macro contents as a
device control command. The devicem request and \Y escape
sequence are each approximately equivalent to “\X'name'”. They
differ from that construction in that the contents of the string
or macro name are not interpreted; futher, 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 output format; their
presence confuses drivers that do not know about it (see
subsection “Device control commands” of groff_out(5)).
The tag and taga requests are reserved for internal use.
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 _i_n 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
: ${varo_p_value}
as output.
The differences between the roff language recognized by GNU troff
and that of AT&T troff, as well as the device, font, and device-
independent intermediate output formats described by CSTR #54 are
documented in groff_diff(7). groff provides an AT&T
compatibility mode. The .cp request and registers .C and .cp set
and test the enablement of this mode.
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); colors
(.pcolor); composite characters (.pcomposite); environments
(.pev); hyphenation exceptions (.phw); registers (.pnr); page
location traps (.ptr); and a list of pending output nodes
corresponding to the previous input line (.pline) to the standard
error stream.
This document was written by 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⟩.
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 output format referred to collectively in
groff documentation as “AT&T troff”.
“A Typesetter-independent TROFF” by Brian W. Kernighan, 1982,
AT&T Bell Laboratories Computing Science Technical Report No. 97
(CSTR #97), provides additional insights into the device and font
description file formats and device-independent output format.
groff(1)
is the preferred interface to the groff system; it manages
the pipeline that carries a source document through
preprocessors, the troff formatter, and an output driver
to viewable or printable form. It also exhaustively lists
the man pages provided with the GNU roff system.
groff_char(7)
discusses character encoding issues, escape sequences that
produce glyphs, and enumerates groff's predefined special
character escape sequences.
groff_diff(7)
covers differences between the GNU troff formatter, its
device and font description file formats, its device-
independent output format, and those of AT&T troff, whose
design it reimplements.
groff_font(5)
describes the formats of the files that describe devices
(DESC) and fonts.
groff_tmac(5)
surveys macro packages provided with groff, describes how
documents can take advantage of them, offers guidance on
writing macro packages and using diversions, and includes
historical information on macro package naming
conventions.
roff(7)
presents a detailed history of roff systems and summarizes
concepts common to them.
This page is part of the groff (GNU troff) project. Information
about the project can be found at
⟨http://www.gnu.org/software/groff/⟩. If you have a bug report
for this manual page, see ⟨http://www.gnu.org/software/groff/⟩.
This page was obtained from the project's upstream Git repository
⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-06-10.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
groff 1.23.0.1273-9d53-dirty 6 June 2024 groff(7)
Pages that refer to this page: man(1), man-pages(7)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|