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groff_diff(7) Miscellaneous Information Manual groff_diff(7)
groff_diff - differences between GNU roff and AT&T troff
The GNU roff text processing system, groff, is an extension of
AT&T troff, the typesetting system originating in Unix systems of
the 1970s. groff removes many arbitrary limitations and adds
features, both to the input language and to the page description
language output by the troff formatter. Differences arising from
groff's implementation of AT&T troff features are also noted. See
roff(7) for background.
GNU troff features identifiers of arbitrary length; supports color
output, non-integral type sizes, and user-defined characters; adds
more conditional expression operators; recognizes additional
scaling units and numeric operators; enables general file I/O (in
“unsafe mode” only); and exposes more formatter state.
Long names
GNU troff introduces many new requests; with three exceptions (cp,
do, rj), they have names longer than two characters. The names of
registers, fonts, strings/macros/diversions, environments, special
characters, streams, and colors can be of any length. Anywhere
AT&T troff supports a parameterized escape sequence that uses an
opening parenthesis “(” to introduce a two-character argument,
groff supports a square-bracketed form “[]” where the argument
within can be of arbitrary length.
Font families, abstract styles, and translation
GNU troff can group text typefaces into families containing each
of the styles “R”, “I”, “B”, and “BI”. So that a document need
not be coupled to a specific font family, 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 document can translate, or
remap, fonts with the ftr request.
Applying the requests cs, bd, tkf, uf, or fspecial to an abstract
style affects the member of the default family corresponding to
that style. The default family can be set with the fam request or
-f command-line option. The styles directive in the output
device's DESC file controls which mounting positions (if any) are
initially associated with abstract styles rather than fonts, and
the sty request can update this association.
Colors
groff supports color output with a variety of color spaces and up
to 16 bits per channel. Some devices, particularly terminals, may
be more limited. When color support is enabled, two colors are
current at any given time: the stroke color, with which glyphs,
rules (lines), and geometric figures are drawn, and the fill
color, which paints the interior of filled geometric figures. The
color, defcolor, gcolor, and fcolor requests; \m and \M escape
sequences; and .color, .m, and .M registers exercise color
support.
Fractional type sizes and new scaling units
AT&T troff interpreted all type size measurements in points.
Combined with integer arithmetic, this design choice made it
impossible to support, for instance, ten and a half-point type.
In GNU troff, an output device can select a scaling factor that
subdivides a point into “scaled points”. A type size expressed in
scaled points can thus represent a non-integral type size.
A scaled point is equal to 1/sizescale points, where sizescale is
specified in the device description file, DESC, and defaults to 1;
see groff_font(5). Requests and escape sequences in GNU troff
interpret arguments that represent a type size in points, which
the formatter multiplies by sizescale and converts to an integer.
Arguments treated in this way comprise those to the escape
sequences \H and \s, to the request ps, the third argument to the
cs request, and the second and fourth arguments to the tkf
request. Scaled points may be specified explicitly with the z
scaling unit. In GNU troff, the register \n[.s] can interpolate a
non-integral type size. The register \n[.ps] interpolates the
type size in scaled points.
For example, if sizescale is 1000, then a scaled point is one
thousandth of a point. Consequently, “.ps 10.5” is synonymous
with “.ps 10.5z”; both set the type size to 10,500 scaled points,
or 10.5 points.
It makes no sense to use the “z” scaling unit in a numeric
expression whose default scaling unit is neither “u” nor “z”, so
GNU troff disallows this. Similarly, it is nonsensical to use a
scaling unit other than “z” or “u” in a numeric expression whose
default scaling unit is “z”, so GNU troff disallows this as well.
Another new scaling unit, “s”, multiplies by the number of basic
units in a scaled point. Thus, “\n[.ps]s” is equal to “1m” by
definition. Do not confuse the “s” and “z” scaling units.
Output devices may be limited in the type sizes they can employ.
The .s and .ps registers represent the type size as selected by
the output driver as it understands a device's capability. The
last requested type size is interpolated in scaled points by the
read-only register .psr and in points as a decimal fraction by the
read-only string-valued register .sr. Both are associated with
the environment. For example, if a type size of 10.95 points is
requested, and the nearest size permitted by a sizes request (or
by the sizes or sizescale directives in the device's DESC file) is
11 points, the output driver uses the latter value.
A further two new measurement units available in groff are “M”,
which indicates hundredths of an em, and “f”, which multiplies by
65,536. The latter provides convenient fractions for color
definitions with the defcolor request. For example, 0.5f equals
32768u.
Numeric expressions
GNU troff permits spaces in a numeric expression within
parentheses, and offers three new operators.
e1>?e2 Interpolate the greater of e1 and e2.
e1<?e2 Interpolate the lesser of e1 and e2.
(c;e) Evaluate e using c as the default scaling unit, ignoring
scaling units in e if c is empty.
Conditional expressions
More conditions can be tested with the “if” and ie requests, as
well as the new “while” request.
c chr True if a character chr is available, where chr is an
ordinary character (Unicode basic Latin excluding control
characters and the space), a special character, or
\N'index'.
d nam True if a string, macro, diversion, or request nam is
defined.
F fnt True if a font fnt is available; fnt can be an abstract
style or a font name. fnt is handled as if it were
accessed with the ft request (that is, abstract styles and
font translation are applied), but fnt cannot be a mounting
position, and no font is mounted.
m col True if a color col is defined.
r reg True if a register reg is defined.
S sty True if a style sty is registered. Font translation
applies.
v Always false. This condition is for compatibility with
certain other troff implementations only. (This refers to
vtroff, a translator that would convert the C/A/T output
from early-vintage AT&T troff to a form suitable for
Versatec and Benson-Varian plotters.)
Drawing commands
GNU troff offers drawing commands to create filled circles and
ellipses, and polygons. Stroked (outlined) objects are drawn with
the stroke color and filled (solid) ones shaded with the fill
color. 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 a stroked
one because the former is drawn only within its defined area,
whereas strokes have a line thickness (set with another new
drawing command, \D't').
Escape sequences
groff introduces several new escape sequences and extends the
syntax of a few AT&T troff escape sequences (namely, \D, \f, \k,
\n, \s, \$, and \*). In the following list, escape sequences are
collated alphabetically at first, and then by symbol roughly in
Unicode code point order.
\A'anything'
Interpolate 1 if anything is a valid identifier, and 0
otherwise. Because invalid input characters are removed,
invalid identifiers are empty or contain spaces, tabs, or
newlines. You can employ \A to validate a macro argument
before using it to construct another escape sequence or
identifier.
\B'anything'
Interpolate 1 if anything is a valid numeric expression,
and 0 otherwise. You might use \B along with the “if”
request to filter out invalid macro arguments.
\D'C d'
Draw filled circle of diameter d with its leftmost point at
the drawing position.
\D'E h v'
Draw filled ellipse with h and v as the axes and the
leftmost point at the drawing position.
\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;
DWB and Heirloom troffs do not. 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 line 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.
\E Embed an escape character that is not interpreted in copy
mode (compare with \a and \t). You can use it to ease the
writing of nested macro definitions. It is also convenient
to define strings containing escape sequences that need to
work when used in copy mode (for example, as macro
arguments), or which will be interpolated at varying macro
nesting depths.
\f[font]
Select font, which may be a mounting position, abstract
style, or font name, to choose the typeface. \f[] and \fP
are synonyms; we recommend the former.
\Ff
\F(fm
\F[family]
Select default font family. \F[] makes the previous font
family the default. \FP is unlike \fP; it selects font
family “P” as the default. See the fam request below.
\k(rg
\k[reg]
Mark horizontal drawing position in two-character register
name rg or arbitrary register name reg.
\mc
\m(cl
\m[col]
Set the stroke color. \m[] restores the previous stroke
color, or the default if there is none.
\Mc
\M(cl
\M[col]
Set the fill color. \M[] restores the previous fill color,
or the default if there is none.
\n[reg]
Interpolate register reg.
\On
\O[n] Suppress troff output of glyphs and geometric objects. The
sequences \O2, \O3, \O4, and \O5 are intended for internal
use by grohtml(1).
\O0
\O1 Disable and enable, respectively, the emission of
glyphs and geometric objects to the output driver,
provided that this sequence occurs at the outermost
suppression level (see \O3 and \O4). Horizontal
motions corresponding to non-overstruck glyph widths
still occur. These sequences also reset the
registers opminx, opminy, opmaxx, and opmaxy to -1.
These four registers mark the top left and bottom
right hand corners of a box encompassing all written
or drawn output.
\O2 At the outermost suppression level, enable emission
of glyphs and geometric objects, and write to the
standard error stream the page number and values of
the four aforementioned registers encompassing
glyphs written since the last interpolation of a \O
sequence, as well as the page offset, line length,
image file name (if any), horizontal and vertical
device motion quanta, and input file name. Numeric
values are in basic units.
\O3
\O4 Begin and end a nested suppression level,
respectively. grohtml uses this mechanism to create
images of output preprocessed with pic, eqn, and
tbl. At startup, troff is at the outermost
suppression level. pre-grohtml generates these
sequences when processing the document, using troff
with the ps output device, Ghostscript, and the PNM
tools to produce images in PNG format. These
sequences start a new page if the device is not html
or xhtml, to reduce the number of images crossing a
page boundary.
\O5[Pfile]
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, corresponding to
left, right, centered, and inline alignments within
the document, respectively. file is is a name
associated with the production of the next image.
\R'name ±n'
Synonymous with “.nr name ±n”.
\s[±n]
\s±[n]
\s'±n'
\s±'n' Set the type size to, or increment or decrement it by, n
scaled points.
\Ve
\V(ev
\V[env]
Interpolate contents of the environment variable env, as
returned by getenv(3). \V is interpreted even in copy
mode.
\X'anything'
Within \X arguments, the escape sequences \&, \), \%, and
\: are ignored; \space and \~ are converted to single space
characters; and \\ is reduced to \. 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 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 definitions are
ignored. Other escape sequences are not supported.
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).
\Ym
\Y(ma
\Y[mac]
Interpolate a macro as a device control command. This is
similar to \X'\*[mac]', except the contents of mac are not
interpreted, and mac can be a macro and thus contain
newlines, whereas the argument to \X cannot. This
inclusion of newlines requires an extension to the AT&T
troff output format, and will confuse postprocessors that
do not know about it.
\Z'anything'
Save the drawing position, format anything, then restore
it. Tabs and leaders in the argument are ignored with an
error diagnostic.
\# Everything up to and including the next newline is ignored.
This escape sequence is interpreted even in copy mode. \#
is like \", except that \" does not ignore a newline; the
latter therefore cannot be used by itself for a whole-line
comment—it leaves a blank line on the input stream.
\$0 Interpolate the name by which the macro being interpreted
was called. In GNU troff this name can vary; see the als
request.
\$(nn
\$[nnn]
In a macro or string definition, interpolate the nnth or
nnnth argument. Macros and strings can have an unlimited
number of arguments.
\$* In a macro or string definition, interpolate the catenation
of all arguments, separated by spaces.
\$@ In a macro or string definition, interpolate the catenation
of all arguments, with each surrounded by double quotes and
separated by spaces.
\$^ In a macro or string definition, interpolate the catenation
of all arguments constructed in a form suitable for passage
to the ds request.
\) Interpolate a transparent dummy character—one that is
ignored by end-of-sentence detection. It behaves as \&,
except that \& is treated as letters and numerals normally
are after “.”, “?”, and “!”; \& cancels end-of-sentence
detection, and \) does not.
\*[string [arg ...]]
Interpolate string, passing it arg ... as arguments.
\/ Apply an italic correction: modify the spacing of the
preceding glyph so that the distance between it and the
following glyph is correct if the latter is of upright
shape. For example, if an italic “f” is followed
immediately by a roman right parenthesis, then in many
fonts the top right portion of the “f” overlaps the top
left of the right parenthesis, which is ugly. Inserting \/
between them avoids this problem. Use this escape sequence
whenever an oblique glyph is immediately followed by an
upright glyph without any intervening space.
\, Apply a left italic correction: modify the spacing of the
following glyph so that the distance between it and the
preceding glyph is correct if the latter is of upright
shape. For example, if a roman left parenthesis is
immediately followed by an italic “f”, then in many fonts
the bottom left portion of the “f” overlaps the bottom of
the left parenthesis, which is ugly. Inserting \, between
them avoids this problem. Use this escape sequence
whenever an upright glyph is followed immediately by an
oblique glyph without any intervening space.
\: Insert a non-printing break point. That is, a word can
break there, but the soft hyphen character does not mark
the break point if it does (in contrast to “\%”). This
escape sequence is an input word boundary, so the remainder
of the word is subject to hyphenation as normal.
\?anything\?
When used in a diversion, this transparently embeds
anything in the diversion. anything is read in copy mode.
When the diversion is reread, anything is interpreted.
anything may not contain newlines; use \! if you want to
embed newlines in a diversion. The escape sequence \? is
also recognized in copy mode and becomes an internal code;
it is this code that terminates anything. Thus
.nr x 1
.nf
.di d
\?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
.di
.nr x 2
.di e
.d
.di
.nr x 3
.di f
.e
.di
.nr x 4
.f
prints 4.
\[char]
Typeset the special character char.
\[base-char combining-component ...]
Typeset a composite glyph consisting of base-char overlaid
with one or more combining-components. For example,
“\[A ho]” is a capital letter “A” with a “hook accent”
(ogonek). See the composite request below; Groff: The GNU
Implementation of troff, the groff Texinfo manual, for
details of composite glyph name construction; and
groff_char(7) for a list of components used in composite
glyph names.
\~ Insert an unbreakable space that is adjustable like an
ordinary space. It is discarded from the end of an output
line if a break is forced.
Restricted requests
To mitigate risks from untrusted input documents, the pi and sy
requests are disabled by default. troff(1)'s -U option enables
the formatter's “unsafe mode”, restoring their function (and
enabling additional groff extension requests, open, opena, and
pso).
New requests
.aln new old
Create alias new for existing register named old, causing
the names to refer to the same stored value. If old is
undefined, a warning in category “reg” is generated and the
request is ignored. To remove a register alias, invoke rr
on its name. A register's contents do not become
inaccessible until it has no more names.
.als new old
Create alias new for existing request, string, macro, or
diversion named old, causing the names to refer to the same
stored object. If old is undefined, a warning in category
“mac” is produced, and the request is ignored. The “am”,
“as”, da, de, di, and ds requests (together with their
variants) create a new object only if the name of the
macro, diversion, or string is currently undefined or if it
is defined as a request; normally, they modify the value of
an existing object. To remove an alias, invoke rm on its
name. The object itself is not destroyed until it has no
more names.
When a request, macro, string, or diversion is aliased,
redefinitions and appendments “write through” alias names.
To replace an alias with a separately defined object, you
must use the rm request on its name first.
.am1 name [end-name]
As “am”, but compatibility mode is disabled while the
appendment to name is interpreted: a “compatibility save”
token is inserted at its beginning, and a “compatibility
restore” token at its end. As a consequence, the requests
“am”, am1, de, and de1 can be intermixed freely since the
compatibility save/restore tokens affect only the parts of
the macro populated by am1 and de1.
.ami name [end-name]
Append to macro indirectly. See dei below.
.ami1 name [end-name]
As ami, but compatibility mode is disabled during
interpretation of the appendment.
.as1 name [contents]
As “as”, but compatibility mode is disabled while the
appendment to name is interpreted: a “compatibility save”
token is inserted at the beginning of contents, and a
“compatibility restore” token after it. As a consequence,
the requests “as”, as1, ds, and ds1 can be intermixed
freely since the compatibility save/restore tokens affect
only the portions of the strings populated by as1 and ds1.
.asciify div
Unformat the diversion div in a way such that Unicode basic
Latin (ASCII) characters, characters translated with the
trin request, space characters, and some escape sequences,
that were formatted in the diversion div are treated like
ordinary input characters when div is reread. Doing so can
be useful in conjunction with the writem request. asciify
can be also used for gross hacks; for example, the
following sets register n to 1.
.tr @.
.di x
@nr n 1
.br
.di
.tr @@
.asciify x
.x
asciify cannot return all items in a diversion to their
source equivalent: nodes such as those produced by \N[...]
will remain nodes, so the result cannot be guaranteed to be
a pure string. See section “Copy mode” in groff(7). Glyph
parameters such as the type face and size are not
preserved; use unformat to achieve that.
.backtrace
Write backtrace of input stack to the standard error
stream. See the -b option of troff(1).
.blm [name]
Set a blank line macro (trap). If a blank line macro is
thus defined, groff executes macro when a blank line is
encountered in the input file, instead of the usual
behavior. A line consisting only of spaces is also treated
as blank and subject to this trap. If no argument is
supplied, the default blank line behavior is
(re-)established.
.box [name]
.boxa [name]
Divert (or append) output to name, similarly to the di and
da requests, respectively. Any pending output line is not
included in the diversion. Without an argument, stop
diverting output; any pending output line inside the
diversion is discarded.
.break Exit a “while” loop. Do not confuse this request with a
typographical break or the br request. See “continue”.
.brp Break and adjust line; this is the AT&T troff escape
sequence \p in request form.
.cflags n c1 c2 ...
Assign properties encoded by the number n to characters c1,
c2, and so on. Ordinary and special characters have
certain associated properties. (Glyphs don't: to GNU
troff, like AT&T device-independent troff, a glyph is an
identifier corresponding to a rectangle with some metrics;
see groff_font(5).) The first argument is the sum of the
desired flags and the remaining arguments are the
characters to be assigned those properties. Spaces between
the cn arguments are optional. Any argument cn can be a
character class defined with the class request rather than
an individual character.
The non-negative integer n is the sum of any of the
following. Some combinations are nonsensical, such as “33”
(1 + 32).
1 Recognize the character as ending a sentence if
followed by a newline or two spaces. Initially,
characters “.?!” have this property.
2 Enable breaks before the character. A line is not
broken at a character with this property unless the
characters on each side both have non-zero
hyphenation codes. This exception can be overridden
by adding 64. Initially, no characters have this
property.
4 Enable breaks after the character. A line is not
broken at a character with this property unless the
characters on each side both have non-zero
hyphenation codes. This exception can be overridden
by adding 64. Initially, characters “-\[hy]\[em]”
have this property.
8 Mark the glyph associated with this character as
overlapping other instances of itself horizontally.
Initially, characters
“\[ul]\[rn]\[ru]\[radicalex]\[sqrtex]” have this
property.
16 Mark the glyph associated with this character as
overlapping other instances of itself vertically.
Initially, the character “\[br]” has this property.
32 Mark the character as transparent for the purpose of
end-of-sentence recognition. In other words, an
end-of-sentence character followed by any number of
characters with this property is treated as the end
of a sentence if followed by a newline or two
spaces. This is the same as having a zero space
factor in TeX. Initially, characters
“'")]*\[dg]\[dd]\[rq]\[cq]” have this property.
64 Ignore hyphenation codes of the surrounding
characters. Use this value in combination with
values 2 and 4. Initially, no characters have this
property.
For example, if you need an automatic break point
after the en-dash in numeric ranges like
“3000–5000”, insert
.cflags 68 \[en]
into your document. However, this can lead to bad
layout if done without thinking; in most situations,
a better solution than changing the cflags value is
inserting “\:” right after the hyphen at the places
that really need a break point.
The remaining values were implemented for East Asian
language support; those who use alphabetic scripts
exclusively can disregard them.
128 Prohibit a break before the character, but allow a
break after the character. This works only in
combination with values 256 and 512 and has no
effect otherwise. Initially, no characters have
this property.
256 Prohibit a break after the character, but allow a
break before the character. This works only in
combination with values 128 and 512 and has no
effect otherwise. Initially, no characters have
this property.
512 Allow a break before or after the character. This
works only in combination with values 128 and 256
and has no effect otherwise. Initially, no
characters have this property.
In contrast to values 2 and 4, the values 128, 256, and 512
work pairwise. If, for example, the left character has
value 512, and the right character 128, no break will be
automatically inserted between them. If we use value 6
instead for the left character, a break after the character
can't be suppressed since the neighboring character on the
right doesn't get examined.
.char c contents
Define the ordinary or special character c as contents,
which can be empty. More precisely, char defines a groff
object (or redefines an existing one) that is accessed with
the name c on input, and produces contents on output.
Every time c is to be formatted, contents is processed in a
temporary environment and the result is wrapped up into a
single object. Compatibility mode is turned off and the
escape character is set to \ while contents is processed.
Any emboldening, constant spacing, or track kerning is
applied to this object as a whole, not to each character in
contents.
An object defined by this request can be used just like a
glyph provided by the output device. In particular, other
characters can be translated to it with the tr request; it
can be made the tab or leader fill character with the tc
and lc requests; sequences of it can be drawn with the \l
and \L escape sequences; and, if the hcode request is used
on c, it is subject to automatic hyphenation.
To prevent infinite recursion, occurrences of c within its
own definition are treated normally (as if it were not
being defined with char). The tr and trin requests take
precedence if char both apply to c. A character definition
can be removed with the rchar request.
.chop object
Remove the last character from the macro, string, or
diversion object. This is useful for removing the newline
from the end of a diversion that is to be interpolated as a
string. This request can be used repeatedly on the same
object; see section “gtroff Internals” in Groff: The GNU
Implementation of troff, the groff Texinfo manual, for
discussion of nodes inserted by groff.
.class name c1 c2 ...
Define a character class (or simply “class”) name
comprising the characters or range expressions c1, c2, and
so on.
A class thus defined can then be referred to in lieu of
listing all the characters within it. Currently, only the
cflags request can handle references to character classes.
In the request's simplest form, each cn is a character (or
special character).
.class [quotes] ' \[aq] \[dq] \[oq] \[cq] \[lq] \[rq]
Since class and special character names share the same name
space, we recommend starting and ending the class name with
“[” and “]”, respectively, to avoid collisions with
existing character names defined by groff or the user (with
char and related requests). This practice applies the
presence of “]” in the class name to prevent the usage of
the special character escape form “\[...]”, thus you must
use the \C escape to access a class with such a name.
You can also use a character range expression consisting of
a start character followed by “-” and then an end
character. Internally, GNU troff converts these two
character names to Unicode code points (according to the
groff glyph list [GGL]), which determine the start and end
values of the range. If that fails, the class definition
is skipped. Furthermore, classes can be nested.
.class [prepunct] , : ; > }
.class [prepunctx] \C'[prepunct]' \[u2013]-\[u2016]
The class “[prepunctx]” thus contains the contents of the
class “[prepunct]” and characters in the range
U+2013–U+2016.
If you want to include “-” in a class, it must be the first
character value in the argument list, otherwise it gets
misinterpreted as part of the range syntax.
It is not possible to use class names as end points of
range definitions.
A typical use of the class request is to control line-
breaking and hyphenation rules as defined by the cflags
request. For example, to inhibit line breaks before the
characters belonging to the “[prepunctx]” class defined in
the previous example, you can write the following.
.cflags 2 \C'[prepunctx]'
.close stream
Close the stream named stream, invalidating it as an
argument to the write request. See open.
.composite c1 c2
Map character name c1 to character name c2 when c1 is a
combining component in a composite glyph. Typically, this
remaps a spacing glyph to a combining one.
.continue
Skip the remainder of a “while” loop's body, immediately
starting the next iteration. See break.
.color n
If n is non-zero or missing, enable colors (the default),
otherwise disable them.
.cp n If n is non-zero or missing, enable compatibility mode,
otherwise disable it. In compatibility mode, long names
are not recognized, and the incompatibilities they cause do
not arise.
.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 components), “cmyk” (four components), or
“gray” (one component). “grey” is accepted as a synonym of
“gray”. The color components can be encoded as a
hexadecimal value starting with # or ##. The former
indicates that each component is in the range 0–255 (0–FF),
the latter the range 0–65535 (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).
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.
.de1 name [end-name]
Define a macro to be interpreted with compatibility mode
disabled. When name is called, compatibility mode
enablement status is saved; it is restored when the call
completes.
.dei name [end-name]
Define macro indirectly, with the name of the macro to be
defined in string name and the name of the end macro
terminating its definition in string end-name.
.dei1 name [end-name]
As dei, but compatibility mode is disabled while the
definition of the macro named in string name is
interpreted.
.device anything
Write anything, read in copy mode, to troff output as a
device control command. An initial neutral double quote is
stripped to allow the embedding of leading spaces.
.devicem name
Write contents of macro or string name to troff output as a
device control command.
.do name [arg ...]
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; that is,
the restored compatibility state applies to the contents of
the macro, string, or diversion name as well as data read
from files or pipes if name is any of the so, soquiet, mso,
msoquiet, or pso requests.
For example,
.de mac1
FOO
..
.de1 mac2
groff
.mac1
..
.de mac3
compatibility
.mac1
..
.de ma
\\$1
..
.cp 1
.do mac1
.do mac2 \" mac2, defined with .de1, calls "mac1"
.do mac3 \" mac3 calls "ma" with argument "c1"
.do mac3 \[ti] \" groff syntax accepted in .do arguments
results in
FOO groff FOO compatibility c1 ~
as output.
.ds1 name contents
As ds, but compatibility mode is disabled while name is
interpreted: a “compatibility save” token is inserted at
the beginning of contents, and a “compatibility restore”
token after it.
.ecr Restore the escape character saved with ecs, or set escape
character to “\” if none has been saved.
.ecs Save the current escape character.
.evc env
Copy the properties of environment env to the current
environment, except for the following data.
• a partially collected line, if present;
• the interruption status of the previous input line (due
to use of the \c escape sequence);
• the count of remaining lines to center, to right-justify,
or to underline (with or without underlined spaces)—these
are set to zero;
• the activation status of temporary indentation;
• input traps and their associated data;
• the activation status of line numbering (which can be
reactivated with “.nm +0”); and
• the count of consecutive hyphenated lines (set to zero).
.fam [family]
Set default font family to family. If no argument is
given, the previous font family is selected, or the
formatter's default family if there is none. The
formatter's default font family is “T” (Times), but it can
be overridden by the output device—see groff_font(5). The
default font family is associated with the environment.
See \F.
.fchar c contents
Define fallback character c as contents. The syntax of
this request is the same as the char request; the
difference is that a character defined with char hides a
glyph with the same name in the selected font, whereas
characters defined with fchar are checked only if c isn't
found in the selected font. This test happens before
special fonts are searched.
.fcolor color
Set the fill color to color. Without an argument, the
previous fill color is selected.
.fschar f c contents
Define fallback special character c for font f as contents.
A character defined by fschar is located after the list of
fonts declared with fspecial is searched but before those
declared with the “special” request.
.fspecial f s1 s2 ...
When font f is selected, fonts s1, s2, ... are treated as
special; that is, they are searched for glyphs not found in
f. Any fonts specified in the “special” request are
searched after s1, s2, and so on. Without s arguments,
fspecial clears the list of fonts treated as special when f
is selected.
.ftr f g
Translate font f to g. Whenever a font named f is referred
to in an \f escape sequence, in the F and S conditional
expression operators, or in the ft, ul, bd, cs, tkf,
special, fspecial, fp, or sty requests, font g is used. If
g is missing or identical to f, then font f is not
translated.
.fzoom f zoom
Set zoom factor zoom for font f. zoom must a non-negative
integer multiple of 1/1000th. If it is missing or is equal
to zero, it means the same as 1000, namely no
magnification. f must be a resolved font name, not an
abstract style.
.gcolor color
Set the stroke color to color. Without an argument, the
previous stroke color is selected.
.hcode c1 code1 [c2 code2] ...
Set the hyphenation code of character c1 to code1, that of
c2 to code2, and so on. A hyphenation code must be an
ordinary character (not a special character escape
sequence) other than a digit. The request is ignored if
given no arguments.
For hyphenation to work, hyphenation codes must be set up.
At startup, groff assigns hyphenation codes to the letters
“a–z” (mapped to themselves), to the letters “A–Z” (mapped
to “a–z”), and zero to all other characters. Normally,
hyphenation patterns contain only lowercase letters which
should be applied regardless of case. In other words, they
assume that the words “ABBOT” and “Abbot” should be
hyphenated exactly as “abbot” is. hcode extends this
principle to letters outside the Unicode basic Latin
alphabet; without it, words containing such letters won't
be hyphenated properly even if the corresponding
hyphenation patterns contain them.
.hla lang
Set the hyphenation language to lang. Hyphenation
exceptions specified with the hw request and hyphenation
patterns and exceptions specified with the hpf and hpfa
requests are associated with the hyphenation language. The
hla request is usually invoked by a localization file,
which is in turn loaded by the troffrc or troffrc-end file;
see the hpf request below. The hyphenation language is
associated with the environment.
.hlm [n]
Set the maximum number of consecutive hyphenated lines
to n. If n is negative, there is no maximum. If omitted,
n is -1. This value is associated with the environment.
Only lines output from a given environment count towards
the maximum associated with that environment. Hyphens
resulting from \% are counted; explicit hyphens are not.
.hpf pattern-file
Read hyphenation patterns from pattern-file. This file is
sought in the same way that macro files are with the mso
request or the -mname command-line option to groff(1) and
troff(1).
The pattern-file should have the same format as (simple)
TeX pattern files. The following scanning rules are
implemented.
• A percent sign starts a comment (up to the end of the
line) even if preceded by a backslash.
• “Digraphs” like \$ are not supported.
• “^^xx” (where each x is 0–9 or a–f) and ^^c (character c
in the code point range 0–127 decimal) are recognized;
other uses of ^ cause an error.
• No macro expansion is performed.
• hpf checks for the expression \patterns{...} (possibly
with whitespace before or after the braces). Everything
between the braces is taken as hyphenation patterns.
Consequently, “{” and “}” are not allowed in patterns.
• Similarly, \hyphenation{...} gives a list of hyphenation
exceptions.
• \endinput is recognized also.
• For backwards compatibility, if \patterns is missing, the
whole file is treated as a list of hyphenation patterns
(but the “%” character is still recognized as the start
of a comment).
Use the hpfcode request (see below) to map the encoding
used in hyphenation pattern files to groff's input
encoding.
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. By default, troffrc loads the
localization file for English. (As of groff 1.23.0,
localization files for Czech (cs), German (de), English
(en), French (fr), Japanese (ja), Swedish (sv), and Chinese
(zh) exist.) For Western languages, the localization file
sets the hyphenation mode and loads hyphenation patterns
and exceptions.
A second call to hpf (for the same language) replaces the
old patterns with the new ones.
Invoking hpf causes an error if there is no hyphenation
language.
If no hpf request is specified (either in the document, in
a file loaded at startup, or in a macro package), GNU troff
won't automatically hyphenate at all.
.hpfa pattern-file
As hpf, except that the hyphenation patterns and exceptions
from pattern-file are appended to the patterns already
applied to the hyphenation language of the environment.
.hpfcode a b [c d] ...
Define mapping values for character codes in pattern files.
This is an older mechanism no longer used by groff's own
macro files; for its successor, see hcode above. hpf or
hpfa apply the mapping after reading or appending to the
active list of patterns. Its arguments are pairs of
character codes—integers from 0 to 255. The request maps
character code a to code b, code c to code d, and so on.
Character codes that would otherwise be invalid in groff
can be used. By default, every code maps to itself except
those for letters “A” to “Z”, which map to those for “a” to
“z”.
.hym [length]
Set the (right) hyphenation margin to length. If the
adjustment mode is not “b” or “n”, the line is not
hyphenated if it is shorter than length. Without an
argument, the default hyphenation margin is reset to its
default value, 0. The default scaling unit is “m”. The
hyphenation margin is associated with the environment. A
negative argument resets the hyphenation margin to zero,
emitting a warning in category “range”.
.hys [hyphenation-space]
Suppress hyphenation of the line in adjustment modes “b” or
“n”, if it can be justified by adding no more than
hyphenation-space extra space to each inter-word space.
Without an argument, the hyphenation space adjustment
threshold is set to its default value, 0. The default
scaling unit is “m”. The hyphenation space adjustment
threshold is associated with the current environment. A
negative argument resets the hyphenation space adjustment
threshold to zero, emitting a warning in category “range”.
.itc n name
As “it”, but lines interrupted with the \c escape sequence
are not applied to the line count.
.kern n
If n is non-zero or missing, enable pairwise kerning (the
default), otherwise disable it.
.length reg anything
Compute the number of characters in anything and return the
count in the register reg. If reg doesn't exist, it is
created. anything is read in copy mode.
.ds xxx abcd\h'3i'efgh
.length yyy \*[xxx]
\n[yyy]
14
.linetabs n
If n is non-zero or missing, enable line-tabs mode,
otherwise disable it (the default). In this mode, tab
stops are computed relative to the start of the pending
output line, instead of the drawing position corresponding
to the start of the input line. Line-tabs mode is a
property of the environment.
For example, the following
.ds x a\t\c
.ds y b\t\c
.ds z c
.ta 1i 3i
\*x
\*y
\*z
yields
a b c
whereas in line-tabs mode, the same input gives
a b c
instead.
.lsm [name]
Set the leading space macro (trap) to name. If there are
leading space characters on an input line, name is invoked
in lieu of the usual roff behavior; the leading spaces are
removed. The count of leading spaces on an input line is
stored in \n[lsn], and the amount of corresponding
horizontal motion in \n[lss], irrespective of whether a
leading space trap is set. When it is, the leading spaces
are removed from the input line, and no motion is produced
before calling name. If no argument is supplied, the
default leading space behavior is (re-)established.
.mso file
As “so”, except that file is sought in the same directories
as arguments to the groff(1) and troff(1) -m command-line
option are (the “tmac path”). If the file name to be
interpolated has the form name.tmac and it isn't found, mso
tries to include tmac.name instead and vice versa. If file
does not exist, a warning in category “file” is emitted and
the request has no other effect.
.msoquiet file
As mso, but no warning is emitted if file does not exist.
.nop anything
Interpret anything as if it were an input line. nop
resembles “.if 1”; it puts a break on the output if
anything is empty. Unlike “if”, it cannot govern
conditional blocks. Its application is to maintain
consistent indentation within macro definitions even when
producing text lines.
.nroff Make the n conditional expression evaluate true and t
false. See troff.
.open stream file
Open file for writing and associate stream with it. See
write and close.
.opena stream file
As open, but if file exists, append to it instead of
truncating it.
.output contents
Emit contents, which are read in copy mode, to the
formatter output; this is similar to \! used in the top-
level diversion. An initial neutral double quote in
contents is stripped to allow the embedding of leading
spaces.
.pev Report the state of the current environment followed by
that of all other environments to the standard error
stream.
.pnr Write the names and values of all currently defined
registers to the standard error stream.
.psbb file
Get the bounding box of a PostScript image file. This file
must conform to Adobe's Document Structuring Conventions;
the request attempts to extract the bounding box values
from a %%BoundingBox comment. After invocation, the x and
y coordinates (in PostScript units) of the lower left and
upper right corners can be found in the registers \n[llx],
\n[lly], \n[urx], and \n[ury], respectively. If an error
occurs, these four registers are set to zero.
.pso command
As “so”, except that input comes from the standard output
stream of command.
.ptr Report the names and vertical positions of all page
location traps to the standard error stream. Empty slots
in the list are shown as well, because they can affect the
visibility of subsequently planted traps.
.pvs ±n
Set the post-vertical line spacing to n; default scaling
unit is “p”. With no argument, the post-vertical line
space is set to its previous value.
In GNU troff, the distance between text baselines consists
of the extra pre-vertical line spacing set by the most
negative \x argument on the pending output line, the
vertical spacing (vs), the extra post-vertical line spacing
set by the most positive \x argument on the pending output
line, and the post-vertical line spacing set by this
request.
.rchar c ...
Remove definition of each ordinary or special character c,
undoing the effect of a char, fchar, or schar request.
Glyphs, which are defined by font description files, cannot
be removed. Spaces and tabs may separate c arguments.
.return
Within a macro, return immediately. If called with an
argument, return twice, namely from the current macro and
from the macro one level higher. No effect otherwise.
.rfschar f c ...
Remove each fallback special character c for font f.
Spaces and tabs may separate c arguments. See fschar.
.rj [n]
Right-align the next n input lines. Without an argument,
right-align the next input line. rj implies “.ce 0”, and
ce implies “.rj 0”.
.rnn r1 r2
Rename register r1 to r2. If r1 doesn't exist, the request
is ignored.
.schar c contents
Define global fallback character c as contents. See char;
the distinction is that a character defined with schar is
located after the list of fonts declared with the special
request but before any mounted special fonts.
.shc [c]
Set the soft hyphen character, inserted when a word is
hyphenated automatically or at a hyphenation character,
to c. If c is omitted, the soft hyphen character is set to
the default, \[hy]. If the selected glyph does not exist
in the font in use at a potential hyphenation point, then
the line is not broken at that point. Neither character
definitions (char and similar) nor translations (tr and
similar) are considered when assigning the soft hyphen
character.
.shift n
In a macro, shift the arguments by n positions: argument i
becomes argument i-n; arguments 1 to n are no longer
available. If n is missing, arguments are shifted by 1.
No effect otherwise.
.sizes s1 s2 ... sn [0]
Set the available type sizes to s1, s2, ... sn scaled
points. The list of sizes can be terminated by an
optional “0”. Each si can also be a range m–n. In
contrast to the device description file directive of the
same name (see groff_font(5)), the argument list can't
extend over more than one line.
.soquiet file
As “so”, but no warning is emitted if file does not exist.
.special f ...
Declare each font f as special, searching it for glyphs not
found in the selected font. Without arguments, this list
of special fonts is made empty.
.spreadwarn [limit]
Emit a break warning if the additional space inserted for
each space between words in an output line adjusted to both
margins with “.ad b” is larger than or equal to limit. A
negative value is treated as zero; an absent argument
toggles the warning on and off without changing limit. The
default scaling unit is m. At startup, spreadwarn is
inactive and limit is 3 m.
For example, “.spreadwarn 0.2m” causes a warning if break
warnings are not suppressed and troff must add 0.2 m or
more for each inter-word space in a line.
.stringdown str
.stringup str
Alter the string named str by replacing each of its bytes
with its lowercase (down) or uppercase (up) version (if one
exists). Special characters (see groff_char(7)) will often
transform in the expected way due to the regular naming
convention for accented characters. When they do not, use
substrings and/or catenation.
.ds resume R\['e]sum\['e]\"
\*[resume]
.stringdown resume
\*[resume]
.stringup resume
\*[resume]
Résumé résumé RÉSUMÉ
.sty n s
Associate abstract style s with font mounting position n.
.substring string start [end]
Replace the string named string with its substring bounded
by the indices start and end, inclusively. The first
character in the string has index 0. If end is omitted, it
is implicitly set to the largest valid value (the string
length minus one). Negative indices count backwards from
the end of the string: the last character has index -1, the
character before the last has index -2, and so on.
.ds xxx abcdefgh
.substring xxx 1 -4
\*[xxx]
bcde
.substring xxx 2
\*[xxx]
de
.tkf f s1 n1 s2 n2
Enable track kerning for font f. When the current font
is f the width of every glyph is increased by an amount
between n1 and n2; when the current type size is less than
or equal to s1 the width is increased by n1; when it is
greater than or equal to s2 the width is increased by n2;
when the type size is greater than or equal to s1 and less
than or equal to s2 the increase in width is a linear
function of the type size.
.tm1 message
As tm request, but strips a leading neutral double quote
from message to allow the embedding of leading spaces.
.tmc message
As tm1 request, but does not append a newline.
.trf file
Transparently output the contents of file file. Each line
is output as if preceded by \!; however, the lines are not
subject to copy-mode interpretation. If the file does not
end with a newline, then a newline is added. Unlike cf,
file cannot contain characters that are invalid as input to
GNU troff.
For example, you can define a macro x containing the
contents of file f, using
.di x
.trf f
.di
.trin abcd
This is the same as the tr request except that the asciify
request uses the character code (if any) before the
character translation. Example:
.trin ax
.di xxx
a
.br
.di
.xxx
.trin aa
.asciify xxx
.xxx
The result is “x a”. Using tr, the result would be “x x”.
.trnt abcd
This is the same as the tr request except that the
translations do not apply to text that is transparently
throughput into a diversion with \!. For example,
.tr ab
.di x
\!.tm a
.di
.x
prints b; if trnt is used instead of tr it prints a.
.troff Make the t conditional expression evaluate true and n
false. See nroff.
.unformat div
Unformat the diversion div. Unlike asciify, unformat
handles only tabs and spaces between words, the latter
usually arising from spaces or newlines in the input. Tabs
are treated as input tokens, and spaces become adjustable
again. The vertical sizes of lines are not preserved, but
glyph information (font, type size, space width, and so on)
is retained.
.vpt n If n is non-zero or missing, enable vertical position traps
(the default), otherwise disable them. Vertical position
traps are those set by the ch, wh, and dt requests.
.warn [n]
Select the categories, or “types”, of reported warnings.
n is the sum of the numeric codes associated with each
warning category that is to be enabled; all other
categories are disabled. The categories and their
associated codes are listed in section “Warnings” of
troff(1). For example, “.warn 0” disables all warnings,
and “.warn 1” disables all warnings except those about
missing glyphs. If no argument is given, all warning
categories are enabled.
.warnscale si
Set the scaling unit used in warnings to si. Valid values
for si are u, i (the default), c, p, and P.
.while cond-expr anything
Evaluate the conditional expression cond-expr, and
repeatedly execute anything unless and until cond-expr
evaluates false. anything, which is often a conditional
block, is referred to as the while request's body.
troff treats the body of a while request similarly to that
of a de request (albeit one not read in copy mode), but
stores it under an internal name and deletes it when the
loop finishes. The operation of a macro containing a while
request can slow significantly if the while body is large.
Each time the macro is executed, the while body is parsed
and stored again. An often better solution—and one that is
more portable, since AT&T troff lacked the while request—is
to instead write a recursive macro. It will be parsed only
once (unless you redefine it). To prevent infinite loops,
the default number of available recursion levels is 1,000
or somewhat less (because things other than macro calls can
be on the input stack). You can disable this protective
measure, or raise the limit, by setting the slimit
register. See section “Debugging” below.
If a while body begins with a conditional block, its
closing brace must end an input line.
The break and continue requests alter a while loop's flow
of control.
.write stream anything
Write anything to stream, which must previously have been
the subject of an open request, followed by a newline.
anything is read in copy mode. An initial neutral double
quote in anything is stripped to allow the embedding of
leading spaces.
.writec stream anything
As write, but without a trailing newline.
.writem stream name
Write the contents of the macro or string name to stream,
which must previously have been the subject of an open
request. name is read in copy mode.
Extended requests
.cf file
In a diversion, embed an object which, when reread, will
cause the contents of file to be copied verbatim to the
output. In AT&T troff, the contents of file are
immediately copied to the output regardless of whether a
diversion is being written to; this behavior is so
anomalous that it must be considered a bug.
.de name [end-name]
.am name [end-name]
.ds name [contents]
.as name [contents]
In compatibility mode, these requests behave similarly to
de1, am1, ds1, and as1, respectively: a “compatibility
save” token is inserted at the beginning, and a
“compatibility restore” token at the end, with
compatibility mode switched on during execution.
.hy n New values 16 and 32 are available; the former enables
hyphenation before the last character in a word, and the
latter enables hyphenation after the first character in a
word.
.ss word-space-size [additional-sentence-space-size]
A second argument sets the amount of additional space
separating sentences on the same output line. If omitted,
this amount is set to word-space-size. Both arguments are
in twelfths of current font's space width (typically one-
fourth to one-third em for Western scripts; see
groff_font(5)). The default for both parameters is 12.
Negative values are erroneous.
.ta [[n1 n2 ... nn ]T r1 r2 ... rn]
groff supports an extended syntax to specify repeating tab
stops after the “T” mark. These values are always taken as
relative distances from the previous tab stop. This is the
idiomatic way to specify tab stops at equal intervals in
groff.
The syntax summary above instructs groff to set tabs at
positions n1, n2, ..., nn, then at nn+r1, nn+r2, ...,
nn+rn, then at nn+rn+r1, nn+rn+r2, ..., nn+rn+rn, and so
on.
New registers
GNU troff exposes more formatter state via many new read-only
registers. Their names often correspond to the requests that
affect them.
\n[.br]
Within a macro call, interpolate 1 if the macro is called
with the “normal” control character (“.” by default), and 0
otherwise. This facility allows the reliable modification
of requests. Using this register outside of a macro
definition makes no sense.
.als bp*orig bp
.de bp
.tm before bp
.ie \\n[.br] .bp*orig
.el 'bp*orig
.tm after bp
..
\n[.C] Interpolate 1 if compatibility mode is in effect,
0 otherwise. See cp.
\n[.cdp]
Interpolate depth of last glyph added to the environment.
It is positive if the glyph extends below the baseline.
\n[.ce]
Interpolate number of input lines remaining to be centered.
\n[.cht]
Interpolate height of last glyph added to the environment.
It is positive if the glyph extends above the baseline.
\n[.color]
Interpolate 1 if colors are enabled, 0 otherwise.
\n[.cp]
Within a “do” request, interpolate the saved value of
compatibility mode (see \n[.C] above).
\n[.csk]
Interpolate skew of last glyph added to the environment.
The skew of a glyph is how far to the right of the center
of a glyph the center of an accent over that glyph should
be placed.
\n[.ev]
Interpolate name of current environment. This is a string-
valued register.
\n[.fam]
Interpolate name of default font family. This is a string-
valued register.
\n[.fn]
Interpolate resolved name of the selected font. This is a
string-valued register.
\n[.fp]
Interpolate next free font mounting position.
\n[.g] Interpolate 1. Test with “if” or ie to check whether GNU
troff is the formatter.
\n[.height]
Interpolate font height. See \H.
\n[.hla]
Interpolate hyphenation language of the environment. This
is a string-valued register.
\n[.hlc]
Interpolate count of immediately preceding consecutive
hyphenated lines in the environment.
\n[.hlm]
Interpolate maximum number of consecutive hyphenated lines
allowed in the environment.
\n[.hy]
Interpolate hyphenation mode of the environment.
\n[.hym]
Inteprolate hyphenation margin of the environment.
\n[.hys]
Interpolate hyphenation space adjustment threshold of the
environment.
\n[.in]
Interpolate indentation amount applicable to the pending
output line.
\n[.int]
Interpolate 1 if the previous output line was interrupted
(ended with \c), 0 otherwise.
\n[.kern]
Interpolate 1 if pairwise kerning is enabled, 0 otherwise.
\n[.lg]
Interpolate ligature mode.
\n[.linetabs]
Interpolate 1 if line-tabs mode is enabled, 0 otherwise.
\n[.ll]
Interpolate line length applicable to the pending output
line.
\n[.lt]
Interpolate title line length.
\n[.m] Interpolate name of the selected stroke color. This is a
string-valued register.
\n[.M] Interpolate name of the selected fill color. This is a
string-valued register.
\n[.ne]
Interpolate amount of space demanded by the most recent ne
request that caused a page location trap to be sprung. See
\n[.trunc].
\n[.nm]
Interpolate 1 if output line numbering is enabled (even if
temporarily suppressed), 0 otherwise.
\n[.ns]
Interpolate 1 if no-space mode is enabled, 0 otherwise.
\n[.O] Interpolate output suppression level. See \O.
\n[.P] Interpolate 1 if the current page is selected for output.
See -o command-line option to troff(1).
\n[.pe]
Interpolate 1 during page ejection, 0 otherwise.
\n[.pn]
Interpolate next page number (either that set by pn, or
that of the current page plus 1).
\n[.ps]
Interpolate type size in scaled points.
\n[.psr]
Interpolate most recently requested type size in scaled
points.
\n[.pvs]
Interpolate post-vertical line spacing amount.
\n[.rj]
Interpolate number of input lines remaining to be right-
aligned.
\n[.slant]
Interpolate font slant. See \S.
\n[.sr]
Interpolate most recently requested type size in points as
a decimal fraction. This is a string-valued register.
\n[.ss]
\n[.sss]
Interpolate values of minimal inter-word space and
additional inter-sentence space, respectively, in twelfths
of the space width of the selected font.
\n[.sty]
Interpolate selected abstract font style, if any. This is
a string-valued register.
\n[.tabs]
Interpolate representation of the tab stop settings in a
form suitable for passage to the ta request.
\n[.trunc]
Interpolate amount of vertical space truncated by the most
recently sprung page location trap, or, if the trap was
sprung by an ne request, minus the amount of vertical
motion produced by the ne request. In other words, at the
point a trap is sprung, \n[.trunc] represents the
difference of what the vertical position would have been
but for the trap, and what the vertical position actually
is. See \n[.ne].
\n[.U] Interpolate 1 if in unsafe mode, 0 otherwise. See -U
command-line option to troff(1).
\n[.vpt]
Interpolate 1 if vertical position traps are enabled,
0 otherwise.
\n[.warn]
Interpolate warning mode. See section “Warnings” of
troff(1).
\n[.x] Interpolate major version number of the running troff
formatter. For example, if the version number is 1.23.0,
then \n[.x] contains 1.
\n[.y] Interpolate minor version number of the running troff
formatter. For example, if the version number is 1.23.0,
then \n[.y] contains 23.
\n[.Y] Interpolate revision number of the running troff formatter.
For example, if the version number is 1.23.0, then \n[.Y]
contains 0.
\n[.zoom]
Interpolate magnification of font, in thousandths, or 0 if
magnification unused. See fzoom.
The following (writable) registers are set by the psbb request.
\n[llx]
\n[lly]
\n[urx]
\n[ury]
Interpolate the (upper, lower, left, right) bounding box
values (in PostScript units) of the most recently processed
PostScript image.
The following (writable) registers are set by the \w escape
sequence.
\n[rst]
\n[rsb] Like \n[st] and \n[sb], but taking account of the heights
and depths of glyphs. In other words, these registers
store the highest and lowest vertical positions attained
by the argument formatted by the \w escape sequence, doing
what AT&T troff documented \n[st] and \n[sb] as doing.
\n[ssc] The amount of horizontal space (possibly negative) that
should be added to the last glyph before a subscript.
\n[skw] How far to right of the center of the last glyph in the \w
argument, the center of an accent from a roman font should
be placed over that glyph.
Other writable registers are as follows. Those relating to date
and time are initialized using localtime(3) at formatter startup.
\n[c.] Interpolate input line number. \n[.c] is a read-only alias
of this register.
\n[hours]
Interpolate number of hours elapsed since midnight.
\n[hp] Interpolate horizontal position relative to that at the
start of the input line.
\n[lsn]
\n[lss]
Interpolate count of leading spaces on input line and
amount of corresponding horizontal motion, respectively.
\n[minutes]
Interpolate number of minutes elapsed in the hour.
\n[seconds]
Interpolate number of seconds elapsed in the minute.
\n[systat]
Interpolate return value of system(3) function executed by
most recent sy request.
\n[slimit]
Interpolates maximum quantity of objects on troff's
internal input stack (default: 1000). If non-positive,
there is no limit: recursion can continue until program
memory is exhausted.
\n[year]
Interpolate Gregorian year. AT&T troff's \[yr]
interpolates the Gregorian year minus 1900.
Miscellaneous
GNU troff predefines one string, .T, containing the argument given
to the -T command-line option, namely the output device (for
example, pdf or utf8). The (read-only) register .T interpolates 1
if GNU troff is run with the -T command-line option, and
0 otherwise.
A font not listed in the output device's DESC file's fonts
directive is automatically mounted at the next available font
position when it is selected. If you mount a font explicitly with
the fp request, you should do so on the first unused position,
which can be found in the .fp register.
Unparameterized string interpolation does not conceal the
arguments to a macro being interpreted. Thus, in a macro
definition, the call of another macro with the existing argument
list,
.xx \\$@
is more efficiently done with
\\*[xx]\\
(that is, with string interpolation). The trailing backslashes
prevent the final newline in the macro definition from being
interpolated, potentially putting an unwanted blank line on the
output. See section “Punning Names” in groff(7).
If a font description file contains pairwise kerning information,
glyphs from that font are kerned. Kerning between two glyphs can
be inhibited by placing a dummy character \& between them.
GNU troff keeps track of the nesting depth of escape sequence
interpolations and other uses of delimiters, as in the tl request
and the output comparison operator (that is, input like 'foo'bar'
as a conditional expression), 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. Use visible characters as delimiters in GNU troff,
not “ASCII” controls like BEL (Control+G). The implementation of
\$@ ensures that the double quotes surrounding an argument appear
at an interpolation depth different from that of the arguments
themselves. Similarly, in bracket-form escape sequences like
\f[ZCMI], a right bracket ] does not end the sequence unless it
occurs at the same interpolation depth as the opening [, so input
like
\f[\*[my-family]\*[my-style]]
works as desired. In compatibility mode, no attention is paid to
the interpolation depth.
In GNU troff, the tr request can map characters to the unbreakable
space escape sequence \~ as a special case (tr normally operates
only on characters). This feature replaces the odd-parity tr
mapping trick used in AT&T troff documents, where a character,
often ~, was “sacrificed” by mapping it to “nothing”, drafting it
into use as an unadjustable, unbreakable space. (This feature was
gratuitous even in early AT&T troff, which supported the \space
escape sequence by 1976.) Often, it makes more sense to use GNU
troff's \~ escape sequence instead, which has been adopted by
every other active troff implementation except that of Illumos, as
well as by the non-troff mandoc. Translation of a character to \~
is unnecessary.
GNU troff permits tabs and spaces after the first dot on a control
line that ends a macro definition.
.if t \{\
. de bar
. nop Hello, I'm 'bar'.
. .
.\}
The page description language output by GNU troff is modeled after
that used by AT&T troff once the latter adopted a device-
independent approach in the early 1980s. Only the differences are
documented here. For a fuller discussion, see groff_out(5).
Glyph and font names can be of arbitrary length; postprocessors
should not assume that they are at most two characters. A glyph
to be formatted is always drawn from the current font; in contrast
to AT&T device-independent troff, drivers need not search special
fonts to find a glyph.
Units
The argument to the s command is in scaled points (units of
points/n, where n is the argument to the sizescale command in the
DESC file). The argument to the “x H” command is also in scaled
points.
Simple commands
If the tcommand directive is present in the output device's DESC
file, GNU troff employs the following two commands.
t xyz...
Typeset word xyz; that is, set a sequence of ordinary
glyphs named x, y, z, ..., terminated by a space or
newline; an optional second integer argument is ignored
(this allows the formatter to generate an even number of
arguments). Each glyph is set at the current drawing
position, and the position is then advanced horizontally by
the glyph's width. A glyph's width is read from its
metrics in the font description file, scaled to the current
type size, and rounded to a multiple of the horizontal
motion quantum. Use the C command to emplace glyphs of
special characters.
u n xyz...
Typeset word xyz with track kerning. As t, but after
placing each glyph, the drawing position is further
advanced horizontally by n basic units.
New commands implement color support.
mc cyan magenta yellow
md
mg gray
mk cyan magenta yellow black
mr red green blue
Set the components of the stroke color with respect to
various color spaces. md resets the stroke color to the
default value. The arguments are integers in the range 0
to 65535.
A new device control subcommand is available.
x u n If n is 1, start underlining of spaces. If n is 0, stop
underlining of spaces. This facility is needed for the cu
request in nroff mode and is ignored otherwise.
Extended drawing commands
GNU pic does not produce troff escape sequences employing these
extensions if its -n option is given.
Df n Set the shade of gray used to fill geometric objects to n,
which must be an integer. 0 corresponds to white and 1000
to black. A grayscale ramp spans the two. A value outside
this range uses the stroke color as the fill color. The
fill color is opaque. Normally the default is black, but
some drivers may provide a way of changing this. Df is
obsolete since 2002, superseded by DFg below.
The corresponding \D'f' escape sequence should not be used:
its argument is rounded to an integer multiple of the
horizontal motion quantum, which can limit the precision
of n.
DC d Draw a filled circle of diameter d with its leftmost point
at the drawing position.
DE h v Draw a filled ellipse, of horizontal axis h and vertical
axis v, with its leftmost point at the drawing position.
Dp dx1dy1...dxndyn
Draw a polygon with, for i=1,...,n+1, its ith vertex at the
drawing position +ij−=Σ11(dxj,dyj). groff output drivers
automatically close polygons, drawing a line from (dxn,dyn)
back to (dx1,dy1). The drawing position is left at the
last specified vertex, but this may change in a future
version of GNU troff. Heirloom Doctools troff, like DWB
troff, by default does not close the polygon. In its groff
compatibility mode, Heirloom closes the polygon but leaves
the drawing position unchanged—that is, at the polygon's
initial drawing position.
At the moment, GNU pic uses this command only to generate
triangles and rectangles.
DP dx1dy1...dxndyn
As Dp, but draw a filled rather than a stroked polygon.
Dt n Set the line thickness to n basic units. AT&T troff output
drivers use a thickness proportional to the type size; this
is the GNU troff default. A negative n requests this
explicitly. An n of zero selects the smallest available
line thickness.
A difficulty arises in how the drawing position should be changed
after the execution of these commands. This has little importance
to most users, since the output of GNU grn and pic does not depend
on it. Given a drawing command of the form Dz x1y1...xnyn, where
z is not c or e, AT&T troff treats each xi as a horizontal motion,
each yi as a vertical one, and therefore assumes that the width of
the drawn object is in=Σ1xi, and its height is in=Σ1yi. (Verify its
assumption about height by examining the st and sb registers after
using such a drawing command in a \w escape sequence). For the
sake of compatibility, GNU troff also follows this rule, even
though it frustrates extensions to the D command that set drawing
parameters rather than rendering objects, producing ugly results
in the case of Dt and Df, or otherwise don't parameterize objects
as a series of vertices, as with GNU troff's filled ellipse, DE.
Thus after executing a D command of the form Dz x1y1...xnyn, the
drawing position should be increased by (in=Σ1xi,in=Σ1yi). In a
future release, GNU troff and its output drivers may abandon the
application of this assumption to drawing commands not explicitly
specified in the AT&T “Troff User's Manual”.
Fill color selection is implemented with another set of
extensions.
DFc cyan magenta yellow
DFd
DFg gray
DFk cyan magenta yellow black
DFr red green blue
Set the components of the fill color as described under the
\M escape sequence above. DFd restores the device's
default fill color. The drawing position is not updated,
in contrast to Df.
Device control syntax extension
GNU troff introduces a line continuation convention, permitting
the argument to the x X command to contain newlines. A newline in
the input is transformed to the sequence “newline+”. When
interpreting an x X command, a postprocessor should therefore be
prepared for a plus sign after a newline; if it occurs, preserve
the newline, discard the plus sign, and continue to collect the
input into the argument of the x X command. A newline not
followed by a plus sign terminates the x X command. An
application of this feature is the embedding of PostScript or PDF
language command streams into troff output.
GNU troff guarantees that the first three output commands it emits
are as follows.
x T device
x res n h v
x init
In addition to AT&T troff's debugging features, GNU troff emits
more error diagnostics when syntactical or semantic nonsense is
encountered and supports several warning categories; the output of
these can be selected with warn. Also see the -E, -w, and -W
options of troff(1). Backtraces can be automatically produced
when errors or warnings occur (the -b option of troff(1)) or
generated on demand (backtrace).
groff also adds more flexible diagnostic output requests (tmc and
tm1). More aspects of formatter state can be examined with
requests that write lists of defined registers (pnr), environments
(pev), and page location traps (ptr) to the standard error stream.
GNU troff's features sometimes cause incompatibilities with
documents written assuming old implementations of troff. Some GNU
extensions to troff are supported by other implementations.
When adjusting to both margins, AT&T troff at first adjusts spaces
starting from the right; GNU troff begins from the left. Both
implementations adjust spaces from opposite ends on alternating
output lines to prevent “rivers” in the text.
GNU troff does not always hyphenate words as AT&T troff does. The
AT&T implementation uses a set of hard-coded rules specific to
U.S. English, while GNU troff uses language-specific hyphenation
pattern files derived from TeX. In some versions of troff there
was limited space to store hyphenation exceptions (arguments to
the hw request); GNU troff has no such restriction.
Long names may be GNU troff's most obvious innovation. AT&T troff
interprets “.dsabcd” as defining a string “ab” with contents “cd”.
Normally, GNU troff interprets this as a call of a macro named
“dsabcd”. AT&T troff also interprets \*[ and \n[ as an
interpolation of a string or register, respectively, called “[”.
In GNU troff, however, the “[” is normally interpreted as
beginning the enclosure of a long identifier. In compatibility
mode, GNU troff interprets names in the traditional way, which
means that they are limited to one or two characters. See the -C
option in troff(1) and, above, the .C and .cp registers, and cp
and “do” requests, for more on compatibility mode.
The register \n[.cp] is specialized and may require a statement of
rationale. When writing macro packages or documents that use GNU
troff features and which may be mixed with other packages or
documents that do not—common scenarios include serial processing
of man pages or use of the “so” or mso requests—you may desire
correct operation regardless of compatibility mode enablement in
the surrounding context. It may occur to you to save the existing
value of \n(.C into a register, say, _C, at the beginning of your
file, turn compatibility mode off with “.cp 0”, then restore it
from that register at the end with “.cp \n(_C”. At the same time,
a modular design of a document or macro package may lead you to
multiple layers of inclusion. You cannot use the same register
name everywhere lest you “clobber” the value from a preceding or
enclosing context. The two-character register name space of AT&T
troff is confining and mnemonically challenging; you may wish to
use GNU troff's more capacious name space. However, attempting
“.nr _my_saved_C \n(.C” will not work in compatibility mode; the
register name is too long. “This is exactly what .do is for,” you
think, “.do nr _my_saved_C \n(.C”. The foregoing will always save
zero to your register, because “do” turns compatibility mode off
while it interprets its argument list. What you need is:
.do nr _my_saved_C \n[.cp]
.cp 0
at the beginning of your file, followed by
.cp \n[_my_saved_C]
.do rr _my_saved_C
at the end. As in the C language, we all have to share one big
name space, so choose a register name that is unlikely to collide
with other uses.
The existence of the .T string is a common feature of post-
CSTR #54 troffs—DWB 3.3, Solaris, Heirloom Doctools, and Plan 9
troff all support it—but valid values are specific to each
implementation. The behavior of the .T register in GNU troff
differs from AT&T troff, which interpolated 1 only if nroff was
the formatter and was called with -T.
The lf request sets the number of the current input line in AT&T
troff, and the next in GNU troff.
AT&T troff had only environments named “0”, “1”, and “2”. In GNU
troff, any number of environments may exist, using any valid
identifiers for their names.
GNU troff normally tracks the interpolation depth of escape
sequence parameters and other delimited structures, but not in
compatibility mode. See section “Miscellaneous” above.
In compatibility mode, the escape sequences \f, \H, \m, \M, \R,
\s, and \S are transparent at the beginning of an input line for
the purpose of recognizing a control character, because they
modify formatter state (\R) or properties of the environment (the
rest) and therefore do not create output nodes. For example, this
code produces bold output in both cases, but the text differs,
.de xx '
Hello!
..
\fB.xx\fP
formatting “.xx” normally and “Hello!” in compatibility mode.
GNU troff request names unrecognized by other troff
implementations will likely be ignored; escape sequences that are
GNU troff extensions are liable to format their function selector
character. For example, the adjustable, non-breaking space escape
sequence \~ is also supported by Heirloom Doctools troff 050915
(September 2005), mandoc 1.9.5 (2009-09-21), neatroff (commit
1c6ab0f6e, 2016-09-13), and Plan 9 from User Space troff (commit
93f8143600, 2022-08-12), but not by Solaris/Illumos troffs, which
will render it as ~.
GNU troff does not allow the use of the escape sequences \|, \^,
\&, \{, \}, \space, \', \`, \-, \_, \!, \%, or \c in identifiers;
AT&T troff does. The \A escape sequence (see subsection “Escape
sequences” above) may be helpful in avoiding their use.
Normally, the syntax form \sn accepts only a single character (a
digit) for n, consistently with other forms that originated in
AT&T troff, like \*, \$, \f, \g, \k, \n, and \z. In compatibility
mode only, a non-zero n must be in the range 4–39. Legacy
documents relying upon this quirk of parsing should be migrated to
another \s form. [Background: The Graphic Systems C/A/T
phototypesetter (the original device target for AT&T troff)
supported only a few discrete type sizes in the range 6–36 points,
so Ossanna contrived a special case in the parser to do what the
user must have meant. Kernighan warned of this in the 1992
revision of CSTR #54 (§2.3), and more recently, McIlroy referred
to it as a “living fossil”.]
Fractional type sizes cause one noteworthy incompatibility. In
AT&T troff the ps request ignores scaling units and thus “.ps 10u”
sets the type size to 10 points, whereas in GNU troff it sets the
type size to 10 scaled points, which may be a much smaller
measurement. See subsection “Fractional type sizes and new
scaling units” above.
The ab request differs from AT&T troff: GNU troff writes no
message to the standard error stream if no arguments are given,
and it exits with a failure status instead of a successful one.
The bp request differs from AT&T troff: GNU troff does not accept
a scaling unit on the argument, a page number; the former
(somewhat uselessly) does.
In AT&T troff the pm request reports macro, string, and diversion
sizes in units of 128-byte blocks, and an argument reduces the
report to a sum of the above in the same units. GNU troff ignores
any arguments and reports the sizes in bytes.
Unlike AT&T troff, GNU troff does not ignore the ss request if the
output is a terminal device; instead, the values of minimum inter-
word and additional inter-sentence space are each rounded down to
the nearest multiple of 12.
In GNU troff there is a fundamental difference between
(unformatted) characters and (formatted) glyphs. Everything that
affects how a glyph is output is stored with the glyph node; once
a glyph node has been constructed, it is unaffected by any
subsequent requests that are executed, including bd, cs, tkf, tr,
or fp requests. Normally, glyphs are constructed from characters
immediately before the glyph is added to an output line. Macros,
diversions, and strings are all, in fact, the same type of object;
they contain a sequence of intermixed character and glyph nodes.
Special characters transform from one to the other: before being
added to the output, they behave as characters; afterward, they
are glyphs. A glyph node does not behave like a character node
when it is processed by a macro: it does not inherit any of the
special properties that the character from which it was
constructed might have had. For example, the input
.di x
\\\\
.br
.di
.x
produces “\\” in GNU troff. Each pair of backslashes becomes one
backslash glyph; the resulting backslashes are thus not
interpreted as escape characters when they are reread as the
diversion is output. AT&T troff would interpret them as escape
characters when rereading them and end up printing one “\”.
One way to format a backslash in most documents is with the \e
escape sequence; this formats the glyph of the current escape
character, regardless of whether it is used in a diversion; it
also works in both GNU troff and AT&T troff. (Naturally, if
you've changed the escape character, you need to prefix the “e”
with whatever it is—and you'll likely get something other than a
backslash in the output.)
The other correct way, appropriate in contexts independent of the
backslash's common use as a roff escape character—perhaps in
discussion of character sets or other programming languages—is the
character escape \(rs or \[rs], for “reverse solidus”, from its
name in the ECMA-6 (ISO/IEC 646) standard. [This escape sequence
is not portable to AT&T troff, but is to its lineal descendant,
Heirloom Doctools troff, as of its 060716 release (July 2006).]
To store an escape sequence in a diversion that is interpreted
when the diversion is reread, either use the traditional \!
transparent output facility, or, if this is unsuitable, the new \?
escape sequence. See subsection “Escape sequences” above and
sections “Diversions” and “gtroff Internals” in Groff: The GNU
Implementation of troff, the groff Texinfo manual.
In the somewhat pathological case where a diversion exists
containing a partially collected line and a partially collected
line at the top-level diversion has never existed, AT&T troff will
output the partially collected line at the end of input; GNU troff
will not.
Formatter output incompatibilities
Its extensions notwithstanding, the groff intermediate output
format has some incompatibilities with that of AT&T troff, but
better compatibility is sought; problem reports and patches are
welcome. The following incompatibilities are known.
• The drawing position after rendering polygons is inconsistent
with AT&T troff practice. Other implementations have diverged
on this point as well.
• The output cannot be easily rescaled to other devices as AT&T
troff's could.
This document was written by James Clark ⟨jjc@jclark.com⟩, Werner
Lemberg ⟨wl@gnu.org⟩, Bernd Warken ⟨groff-bernd.warken-72@web.de⟩,
and G. Branden Robinson ⟨g.branden.robinson@gmail.com⟩.
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 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,
provides additional insights into the device and font description
file formats and output format.
groff(1), groff(7), roff(7)
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 tarball groff-1.23.0.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/groff/⟩ on 2026-01-16. 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 2 July 2023 groff_diff(7)
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