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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 a reimplementation
and 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
can operate in a mode that increases support for documents written
for AT&T troff; see section “Compatibility mode” below.
GNU troff features identifiers of arbitrary length; supports color
output, non-integral type sizes, user-defined characters, and
automatic hyphenation of languages other than English; 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, character classes, streams, hyphenation language
codes, 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. For example,
groff ships with support for families containing each of the
styles “R”, “I”, “B”, and “BI” (roman [upright], bold, italic
[slanted], and bold-italic). 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 combine with a style dynamically, producing a
resolved font name. A document can translate, or remap, font
names 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.
Hyphenation
GNU troff uses a hyphenation algorithm and language-specific
pattern files (based on TeX's) to decide which words can be
hyphenated and where. AT&T troff's hyphenation system (“suftab”)
was specific to English.
New requests permit finer control over hyphenation breaking;
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 hla request selects a
hyphenation language, whereas hpf and hpfa load (or append to) the
language's hyphenation patterns. If no hyphenation language is
set or no patterns are loaded, GNU troff does not perform
automatic hyphenation.
For automatic hyphenation to work, the formatter must know which
letters are equivalent; for example, the letter “E” behaves like
“e”; only the latter typically appears in hyphenation pattern
files. GNU troff expects characters that participate in automatic
hyphenation to be assigned hyphenation codes that define these
equivalence classes. At startup, GNU troff assigns hyphenation
codes to the letters “a”–“z”, applies the same codes to “A”–“Z” in
one-to-one correspondence, and assigns a code of zero to all other
characters.
The hcode request extends this principle to letters outside the
Unicode basic Latin set; without it, words containing such letters
won't hyphenate properly even if the corresponding hyphenation
patterns contain them.
GNU troff's \: escape sequence is analogous to the \% sequence but
produces no hyphen if the word breaks at that location.
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 size in points.
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.
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.
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
scaling units other than “p”, “s”, “z”, or “u”, in a numeric
expression whose default scaling unit is “z”, and so GNU troff
disallows those as well.
Output devices may be limited in the type sizes they can employ.
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. The .s and .ps registers
represent the type size selected by the formatter 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.
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 expressions e1 and e2.
e1<?e2 Interpolate the lesser of expressions e1 and e2.
(c;e) Evaluate expression e using c as the default scaling unit,
ignoring scaling units in e if c is empty.
Arithmetic in GNU troff saturates instead of wrapping.
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; chr is an ordinary or
special character (whether built-in or user-defined) 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 an
argument to the ft request (that is, the default family is
combined with an abstract style and font translation is
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 an abstract style sty is registered. Font
translations apply.
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
command. A filled figure is smaller than a stroked one with the
same parameters because the former is drawn only within its
defined area, whereas strokes have a line thickness, set with
another new drawing command.
Escape sequences
groff introduces several new escape sequences, extends the syntax
of a few AT&T troff escape sequences (namely, \D, \f, \k, \n, \s,
\$, and \*), and alters the behavior of \X. The following list
collates escape sequences 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 GNU troff ignores any input character
with an invalid code when reading it, invalid identifiers
are empty or contain spaces, tabs, newlines, or escape
sequences that interpolate something other than a sequence
of ordinary characters. 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 axis lengths h, v, and its
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. groff does not
specify how the output device must fill concave or self-
intersecting polygons.
\D't n'
Set line thickness of geometric objects to n basic units.
A zero n selects the minimum supported thickness. A
negative n (the default) selects a thickness proportional
to the type size.
\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[fnt]
Select typeface fnt, which may be a mounting position,
abstract style, or font name. \f[] and \fP are synonyms;
we recommend the former.
\Ff
\F(fm
\F[fml]
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 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 system environment variable env
(one-character name e, two-character name ev) as returned
by getenv(3). \V is interpreted even in copy mode.
\X'character-sequence'
Unlike AT&T troff, GNU troff performs some limited
processing of the sequence of ordinary characters, special
characters, and spaces in character-sequence.
The formatter's special character repertoire is unknown to
output drivers outside of glyphs named in a device's fonts,
and even then they may not possess complete coverage of the
names documented in groff_char(7). Further, escape
sequences that produce horizontal or vertical motions,
hyphenation breaks, or that are dummy characters may appear
in strings or be converted to nodes, particularly in
diversions. When they occur in a device extension command,
they produce warnings in category “char”. These are not
representable when interpolated directly into device-
independent output, as might be done when writing out tag
names for PDF bookmarks, which can appear in a viewer's
navigation pane. This is also the case for a small number
of special characters, such as \[ru], the baseline rule,
that lack a Unicode definition.
So that any Unicode code point can be represented in device
extension commands, for example in an author's name in
document metadata or as a usefully named bookmark or
hyperlink anchor, GNU troff transforms its argument to
represent characters outside the Unicode Basic Latin range
as Unicode code points expressed in groff's notation for
these, “\[uXXXX]”; see groff_char(7). For these
transformations, the formatter ignores character
translations and definitions.
GNU troff converts several ordinary characters that typeset
as non-basic Latin code points to code points outside that
range so that they are used consistently whether they are
formatted as glyphs or used in a device extension command
argument. These ordinary characters are “'”, “-”, “^”,
“`”, and “~”; others are written as-is. Thus, “'”
transforms to “\[u2019]”.
Contrariwise, GNU troff translates special characters that
typeset as Unicode basic Latin characters to basic Latin
characters accordingly. Thus, “\[ga]” transforms to “`”,
“\[Do]” to “$”, and so on.
\Ym
\Y(ma
\Y[mac]
Interpolate a macro as a device extension command. As
\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 page description language, and confuses
postprocessors that do not know about it.
\Z'anything'
Save the drawing position, format anything (except tabs and
leaders), then restore it.
\# Read everything up to and including the next newline in
copy mode and discard it. \# 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 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 “\%”). The
remainder of the word is subject to hyphenation as normal.
\?anything\?
Suppress formatting of anything. This feature has two
applications.
Use it with the output comparison operator to compare its
operands by character rather than as formatted output.
Since troff() reads comparands protected with \? in copy
mode, they need not even be valid groff syntax. The escape
character is still lexically recognized, however, and
consumes the next character.
When used in a diversion, \? transparently embeds input,
read in copy mode, until its own next occurrence on the
input line. Use \! if you want to embed newlines in a
diversion. Unlike \!, \? is interpreted even in copy mode,
and anything in the top-level diversion is not sent to
device-independent output.
\[char]
Typeset the special character char. See groff_char(7).
\[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 cf, 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
Several GNU troff requests work like AT&T troff's “as” and ds
requests, accepting an optional leading neutral double-quote,
notated “["]”, in an argument that the formatter reads in copy
mode to the end of the input line, permitting inclusion of leading
spaces.
.aln new-register existing-register
Create alias (additional name) new-register of existing-
register. If existing-register is undefined, GNU troff
produces a warning in category “reg” and ignores the
request. See section “Warnings” of groff(1), regarding the
enablement and suppression of warnings. 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-name existing-name
Create alias (additional name) new-name of request, string,
macro, or diversion existing-name, causing the names to
refer to the same stored object. If new-name already
exists, its contents are lost unless already aliased. If
existing-name is undefined, GNU troff produces a warning in
category “mac” and ignores the request. See section
“Warnings” of groff(1), regarding the enablement and
suppression of warnings. 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,
remove 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 (US-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 interpolated. Doing
so can be useful in conjunction with the writem request.
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 name when a blank line is
encountered in the input, 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 need
not separate the cn arguments. 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.
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 an ordinary or special character c as contents. If
contents is absent, an existing character definition made
with the same request is deleted.
Defining (or redefining) a character c creates a formatter
object that is recognized like any other ordinary or
special character on input, and produces contents on
output. Every time c is to be output, contents is
processed in a temporary environment and the result
encapsulated in a node. (See section “Gtroff Internals” in
Groff: The GNU Implementation of troff, the groff Texinfo
manual.) Compatibility mode is disabled and the escape
character 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.
A character defined by char 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 also applies to c. A character
definition can be removed with the rchar request.
.chop name
Remove the last character from the macro, string, or
diversion name. 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
name; see section “Gtroff Internals” in Groff: The GNU
Implementation of troff, the groff Texinfo manual, for
discussion of nodes inserted by groff.
.class ident c ...
Define a character class (or simply “class”) ident
comprising the characters or range expressions c. 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 c is an ordinary or special
character.
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 sequence 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.
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.
.close stream
Close the named stream, invalidating it as an argument to
the write request. See open.
.composite c1 c2
Map ordinary or special character c1 to c2 when c1 is a
combining component in a composite character. Typically,
composite is used to map a spacing character to a combining
one. See groff_char(7).
.continue
Skip the remainder of a “while” loop's body, immediately
retesting its conditional expression. See break.
.color [b]
Enable or disable output of color-related device-
independent output commands per Boolean expression b. It
is enabled by default, and if b is omitted.
.cp [b]
Enable or disable AT&T troff compatibility mode per Boolean
expression b. It is disabled by default, and enabled if b
is omitted. 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”. Each color component 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, a
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 ident [end-name]
As “de”, but compatibility mode is disabled while the macro
ident is interpreted: a “compatibility save” token is
inserted at its beginning, and a “compatibility restore”
token at its end. See .am1.
.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 [["]character-sequence]
Write character-sequence, a sequence of ordinary or special
characters and spaces read in copy mode, to troff output as
the argument to a device extension command.
.devicem name
Write contents of macro or string name to troff output as
the argument to a device extension 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 interpolation 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.
.ds1 name [["]contents]
As ds, but GNU troff disables AT&T compatibility mode while
interpreting name: it inserts a “compatibility save” token
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:
• 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-align,
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).
Copying an environment to itself discards the foregoing
data.
.fam [fml]
Set default font family to fml. With no argument, the
previous font family is selected, and if none, the
formatter's default family. This default is “T” (Times),
but 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. 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. This test happens before special
fonts are searched.
.fcolor [col]
Set the fill color to col, or, without an argument, restore
the previous stroke color, or the default if there is none.
.fschar f c [["]contents]
Define fallback special character c for 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 f [s ...]
When font f is selected, treat each font s as special; that
is, search it for any glyph not found in f. Fonts
specified by the “special” request are searched after those
listed in the fspecial request. Without s arguments,
fspecial empties 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; it scales the magnification by thousandths with
1000 as a basis. If zoom is missing or equal to zero or
1000, font f is not magnified. f must be a resolved font
name, not an abstract style or mounting position.
.gcolor [col]
Set the stroke color to col, or, without an argument,
restore the previous stroke color, or the default if there
is none.
.hcode dst1 src1 [dst2 src2] ...
Set the hyphenation code of character dst1 to that of src1,
and so on. dst1 must be an ordinary character (other than
a numeral) or a special character, and src1 must be an
ordinary character (other than a numeral) or a special
character to which a hyphenation code has already been
applied. Assigning the code of an ordinary character to
itself effectively creates a unique hyphenation code (which
can then be copied to others). hcode ignores spaces
between arguments. If any argument is invalid, hcode
reports an error and stops reading them.
.hla [lang]
Set the hyphenation language to lang, or clear it if there
is no argument. 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 consecutive automatically hyphenated line limit to
n. A negative value means “no limit”. Omitting n implies
a limit of -1. This value is associated with the
environment. Only lines output from a given environment
count toward 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.
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 backward 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 hcode 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] ...
Caution: This request will be withdrawn in a future groff
release. Use hcode instead.
Define mapping values for character codes in pattern files.
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 GNU
troff 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”.
.hydefault mode
Set hyphenation mode default to mode. When the hy request
is invoked without an argument, this mode is selected. The
hyphenation mode default is associated with the
environment. The formatter's default is 1 for AT&T troff
compatibility. groff locale files generally set a more
appropriate one; see groff_tmac(5).
.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 that adjustment can be achieved 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 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 [b]
Enable or disable pairwise kerning of glyphs in the
environment per Boolean expression b. It is enabled by
default, and if b is omitted.
.length reg [["]contents]
Compute the number of characters in contents and store the
count in the register reg. If reg doesn't exist, it is
created.
.linetabs [b]
Activate or deactivate line-tabs in the environment per
Boolean expression b. They are inactive by default, and
activated if b is omitted. When line-tabs are active, 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.
.lsm [name]
Set a leading space trap, calling the macro name when GNU
troff encounters leading spaces on a text line; the
implicit line break that normally happens in this case is
suppressed. The formatter stores the count of leading
spaces on the text line in register lsn, and the amount of
corresponding horizontal motion in register lss,
irrespective of whether a leading space trap is set. When
it is, GNU troff removes the leading spaces from the input
line and produces no motion before calling name.
If no argument is supplied, GNU troff reëstablishes the
default handling of leading spaces on text lines (breaking
the line when filling, and formatting a horizontal motion
of \n[lsn] word spaces).
.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 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
formatting output.
.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 ["]character-sequence
Emit character-sequence, a sequence of ordinary characters
and spaces read in copy mode, “transparently” (directly) to
troff's output. This usage is similar to that of \! in the
top-level diversion.
.pcolor [col ...]
Report, to the standard error stream, each defined color
named col, its color space identifier, and channel value
assignments, or, without arguments, those of all defined
colors. 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.
.phcode c ...
Report, to the standard error stream, the hyphenation code
of each ordinary or special character c. Special
characters are listed in bracketed syntax using the default
escape character.
.phw Report, to the standard error stream, the list of
hyphenation exceptions associated with the current
hyphenation language. 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 (*).
.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.
.pnr [reg ...]
Report the name and value and, if the value is numeric, the
assigned format of each register reg, or, without
arguments, those of all 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, which is passed to popen(3).
.pstream
Report, to the standard error stream, the name of each open
stream, the name of the file backing it, and its mode
(writing or appending).
.ptr Report the names and vertical positions of all page
location traps to the standard error stream. GNU troff
reports empty slots in the list, where a trap had been
planted but subsequently (re)moved, because they can affect
the visibility of subsequently planted traps.
.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 [anything]
In a macro definition, stop interpretation, skipping to its
end. Do not confuse “return” with rt. If called with an
argument anything, the skip is performed twice—once within
the macro being interpreted and once in an enclosing macro,
permitting a macro to wrap the request.
.rfschar f c ...
Remove each fallback special character c for font f.
Spaces need not separate c arguments. See fschar.
.rj [n]
Break, right-align the next n (default: 1) input lines,
then break again. rj implies “.ce 0”, and ce implies “.rj
0”. If invoked with the no-break control character, the
first break is suppressed.
.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. 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 [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 definition, shift 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.
.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 [s ...]
Declare each font s as special, searching it for glyphs not
found in the selected font. Without arguments, “special”
empties this list of special fonts.
.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” warns if troff must add
0.2 m or more to 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.
.sty pos style
Associate abstract style with non-negative font mounting
position pos.
.substring str start [end]
Replace the string named str with its substring bounded by
the indices start and end, inclusively. The first
character in the string has index 0. Negative indices
count backward from the end of the string: the last
character has index -1, the character before the last has
index -2, and so on. If end is omitted, -1 is implied.
.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, but recognizes and strips a leading neutral double
quote, allowing embedded leading spaces in message.
.tmc [["]message]
As tm1 request, but does not append a newline.
.trf file
Break and copy file as “throughput” to GNU troff output,
discarding characters that are invalid as input; contrast
with cf. Each line of file is output as if preceded by \!,
but is not interpreted by the formatter. If file does not
end with a newline, trf appends one.
.trin abcd
This is the same as the tr request except that the asciify
request uses the character code (if any) before the
character translation.
.trnt abcd
This is the same as the tr request except that the
translations do not apply to text that is transparently
throughput into a diversion with \!.
.troff Make the 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 [b]
Enable or disable vertical position traps per Boolean
expression b. They are enabled by default, and if b is
omitted. Vertical position traps are those set by the ch,
wh, and dt requests. Vertical position trap enablement is
global.
.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.
GNU troff treats the body of a “while” request similarly to
that of a de request (albeit one not read in copy mode),
but stores it under an internal name and deletes it when
the loop finishes. The operation of a macro containing a
“while” request can slow significantly if its body is
large. Each time 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 alter 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 [["]character-sequence]
Write character-sequence, a sequence of ordinary
characters, spaces, or tabs read in copy mode, to stream,
which must previously have been the subject of an “open”
(or opena) request, followed by a newline. GNU troff
flushes the stream after writing to it.
.writec stream [["]character-sequence]
As write, but does not append a newline to contents.
.writem stream name
Write the contents of the macro or string name to stream,
which must previously have been the subject of an “open”
(or opena) request. The contents of name are read in copy
mode.
Altered requests
.bd special-font font
Stop emboldening special-font when font is selected.
special-font must be a font name, not a mounting position.
.cf ["]file
In a diversion, embed an object which, when interpolated,
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.
GNU troff strips a leading neutral double quote from the
argument, allowing it to contain embedded leading spaces.
Further, spaces in file are accepted as part of the file
name.
.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 interpolation of the
applicable macro definition, appendment, or string
contents.
.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. If invoked without an argument, the mode configured
by the hydefault request is selected.
.nx [["]file]
GNU troff strips a leading neutral double quote from the
optional argument, allowing it to contain embedded leading
spaces. Further, spaces in file are accepted as part of
the file name.
.pi ["]command
GNU troff strips a leading neutral double quote from the
argument, allowing it to contain embedded leading spaces.
.so ["]file
GNU troff strips a leading neutral double quote from the
argument, allowing it to contain embedded leading spaces.
Further, spaces in file are accepted as part of the file
name.
.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.
.sy ["]command
GNU troff strips a leading neutral double quote from the
argument, allowing it to contain embedded leading spaces.
.ta [[n1 n2 ... nn ]T r1 r2 ... rn]
GNU troff 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. GNU troff's startup value is “T 0.5i”.
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.
Altered registers
\n[.R] Because GNU troff dynamically manages register storage, it
repurposes the .R register to interpolate the maximum
integer representable in the formatter. Favor its use over
numeric literals with many zeros or nines to indicate an
arbitrary large quantity.
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 definition, 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.
\n[.C] Interpolate 1 if AT&T troff 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
in the environment.
\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 color output is 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 is to be
placed.
\n[.ev]
Interpolate name of current environment. This is a string-
valued register.
\n[.fam]
Interpolate name of the environment's default font family.
This is a string-valued register.
\n[.fn]
Interpolate resolved name of the font selected in the
environment. This is a string-valued register.
\n[.fp]
Interpolate next free non-zero font mounting position.
\n[.g] Interpolate 1. Test with “if” or ie to check whether GNU
troff is the formatter.
\n[.height]
Interpolate height of the environment's selected font. 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 automatic hyphenation mode of the environment.
\n[.hydefault]
Interpolate hyphenation mode default 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 output
line pending in the environment.
\n[.int]
Interpolate 1 if the text most recently formatted in the
environment was “interrupted” or continued with \c),
0 otherwise.
\n[.it]
Interpolate the count of lines remaining in the
environment's pending input trap.
\n[.itc]
Interpolate 1 if the environment's pending input trap
honors the output line continuation escape sequence (\c),
0 otherwise.
\n[.itm]
Interpolate the name of the macro associated with the
environment's pending input trap. This is a string-valued
register.
\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 in the
environment, 0 otherwise.
\n[.ll]
Interpolate line length applicable to the environment's
pending output line.
\n[.lt]
Interpolate the environment's 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 sprung a page location trap. See \n[.trunc].
\n[.nm]
Interpolate 1 if output line numbering is enabled in the
environment (even if temporarily suppressed), 0 otherwise.
\n[.nn]
Interpolate count of output lines remaining in the
environment to have numbering suppressed.
\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 the environment's type size in scaled points.
\n[.psr]
Interpolate the environment's most recently requested type
size in scaled points.
\n[.pvs]
Interpolate the environment's post-vertical line spacing
amount.
\n[.rj]
Interpolate number of input lines remaining to be right-
aligned in the environment.
\n[.slant]
Interpolate slant in degrees of the environment's selected
font. See \S.
\n[.sr]
Interpolate the environment's most recently requested type
size in points as a decimal fraction. This is a string-
valued register.
\n[.ss]
\n[.sss]
Interpolate values of the environment's minimum inter-word
space and additional inter-sentence space, respectively, in
twelfths of the space width of the selected font.
\n[.sty]
Interpolate the environment's selected abstract font style,
if any. This is a string-valued register.
\n[.tabs]
Interpolate the environment's tab stop settings (if any) in
a form suitable for passage to the ta request. This is a
string-valued register.
\n[.trap]
Interpolate the name of the next vertical position trap
after the vertical drawing position. This is a string-
valued register.
\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 the environment's selected
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 (possibly negative) horizontal space to add
to the last glyph before a subscript.
\n[skw]
How far to right of the center of the last glyph in the \w
argument, to place the center of an accent from a roman
font 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 \n[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 US-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 [. 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.
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). Examine more aspects of formatter state with requests that
write lists of defined colors (pcolor), composite characters
(pcomposite), environments (pev), hyphenation codes (phcode),
hyphenation exceptions (phw), registers (pnr), open streams
(pstream), page location traps (ptr), and a list of output nodes
corresponding to the pending input line (pline) to the standard
error stream.
Some syntactical and behavioral differences between AT&T and GNU
troffs are thought too important to neglect; GNU troff therefore
makes available a compatibility mode in an effort to keep
documents prepared for AT&T troff rendering well.
Identifier names of arbitrary length 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.
In compatibility mode, GNU troff accepts several characters as
delimiters that it ordinarily rejects, because they are meaningful
in numeric expressions and therefore potentially ambiguous to the
document maintainer. The set of additional delimiters comprises
“0123456789+-/*%<>=&:().”.
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.
AT&T troff discards trailing spaces from input lines, like GNU
troff, but when it does so, AT&T troff also cancels end-of-
sentence detection. Use of the dummy character escape sequence \&
is more portable.
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.
GNU troff handles the dummy character \& differently from AT&T
troff when it is followed by the hyphenation control escape
sequence \% at the beginning of a word. GNU troff does not regard
the dummy character as “starting” the word; AT&T troff does.
Further, Heirloom Doctools troff does not honor an explicit
hyphenation point marked with \% after a word-initial one.
The existence of the .T string is a common feature of post-
CSTR #97 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.
The escape sequences \f, \H, \m, \M, \R, \s, and \S are
transparent at the beginning of an input line only in
compatibility mode. That is, upon interpreting them, GNU troff no
longer recognizes a control character on the input line; AT&T
troff does.
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 size support causes an 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.
AT&T troff ignores the ss request if the output is a terminal
device; GNU troff rounds down the values of minimum inter-word and
additional inter-sentence space each to the nearest multiple
of 12.
GNU troff strips a leading neutral double quote from the argument
to the cf, nx, pi, and so, and sy requests, allowing it to contain
embedded leading spaces.
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.
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 interpolated, 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 a partially collected but otherwise empty line (as if “\c”
were in the top-level diversion) at the end of input; GNU troff
will not.
Formatter output incompatibilities
Its extensions notwithstanding, GNU troff's page description
language 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 ⟨[email protected]⟩, Werner
Lemberg ⟨[email protected]⟩, Bernd Warken ⟨[email protected]⟩,
and G. Branden Robinson ⟨[email protected]⟩.
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 page description language referred to collectively in groff
documentation as AT&T troff.
“A Typesetter-independent TROFF” by Brian W. Kernighan, 1982, AT&T
Bell Laboratories Computing Science Technical Report No. 97,
provides additional insights into the device and font description
file formats and page description language.
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 project's upstream Git repository
⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2025-02-02. (At
that time, the date of the most recent commit that was found in
the repository was 2025-01-28.) 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
[email protected]
groff 1.23.0.2782-1eed3-dirty 2025-02-01 groff_diff(7)
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