GROFF_DIFF(7) Miscellaneous Information Manual GROFF_DIFF(7)
NAME
groff_diff - differences between GNU troff and classical troff
DESCRIPTION
This manual page describes the language differences between groff, the
GNU roff text processing system, and the classical roff formatter of
the freely available Unix 7 of the 1970s, documented in the Troff
User's Manual by Ossanna and Kernighan. This includes the roff lan-
guage as well as the intermediate output format (troff output).
Section “See Also” below gives pointers to both the classical roff and
the modern groff documentation.
GROFF LANGUAGE
In this section, all additional features of groff compared to the clas-
sical Unix 7 troff are described in detail.
Long names
The names of number registers, fonts, strings/macros/diversions, spe-
cial characters (glyphs), and colors can be of any length. In escape
sequences, additionally to the classical ‘(xx’ construction for a two-
character glyph name, you can use ‘[xxx]’ for a name of arbitrary
length.
\[xxx] Print the special character (glyph) called xxx.
\[comp1 comp2 ...]
Print composite glyph consisting of multiple components. Exam-
ple: ‘\[A ho]’ is capital letter A with ogonek which finally
maps to glyph name ‘u0041_0328’. See Groff: The GNU Implementa-
tion of troff, the groff Texinfo manual, for details of how a
glyph name for a composite glyph is constructed, and
groff_char(7) for a list of glyph name components used in com-
posite glyph names.
\f[xxx]
Set font xxx. Additionally, \f[] is a new syntax form equal to
\fP, i.e., to return to the previous font.
\*[xxx arg1 arg2 ...]
Interpolate string xxx, taking arg1, arg2, ..., as arguments.
\n[xxx]
Interpolate number register xxx.
Fractional point sizes
A scaled point is equal to 1/sizescale points, where sizescale is spec-
ified in the DESC file (1 by default). There is a new scale indica-
tor z that has the effect of multiplying by sizescale. Requests and
escape sequences in troff interpret arguments that represent a point
size as being in units of scaled points, but they evaluate each such
argument using a default scale indicator of z. Arguments treated in
this way are the argument to the ps request, the third argument to the
cs request, the second and fourth arguments to the tkf request, the ar-
gument to the \H escape sequence, and those variants of the \s escape
sequence that take a numeric expression as their argument.
For example, suppose sizescale is 1000; then a scaled point is equiva-
lent to a millipoint; the call .ps 10.25 is equivalent to .ps 10.25z
and so sets the point size to 10250 scaled points, which is equal to
10.25 points.
The number register \n[.s] returns the point size in points as decimal
fraction. There is also a new number register \n[.ps] that returns the
point size in scaled points.
It would make no sense to use the z scale indicator in a numeric ex-
pression whose default scale indicator was neither u nor z, and so
troff disallows this. Similarly it would make no sense to use a scal-
ing indicator other than z or u in a numeric expression whose default
scale indicator was z, and so troff disallows this as well.
There is also new scale indicator s which multiplies by the number of
units in a scaled point. So, for example, \n[.ps]s is equal to 1m. Be
sure not to confuse the s and z scale indicators.
Numeric expressions
Spaces are permitted in a number expression within parentheses.
M indicates a scale of 100ths of an em. f indicates a scale of 65536
units, providing fractions for color definitions with the defcolor re-
quest. For example, 0.5f = 32768u.
e1>?e2 The maximum of e1 and e2.
e1<?e2 The minimum of e1 and e2.
(c;e) Evaluate e using c as the default scaling indicator. If c is
missing, ignore scaling indicators in the evaluation of e.
New escape sequences
\A'anything'
This expands to 1 or 0, depending on whether anything is or is
not acceptable as the name of a string, macro, diversion, number
register, environment, font, or color. It returns 0 if anything
is empty. This is useful if you want to look up user input in
some sort of associative table.
\B'anything'
This expands to 1 or 0, depending on whether anything is or is
not a valid numeric expression. It returns 0 if anything is
empty.
\C'xxx'
Typeset glyph named xxx. Normally it is more convenient to use
\[xxx]. But \C has the advantage that it is compatible with re-
cent versions of Unix and is available in compatibility mode.
\E This is equivalent to an escape character, but it is not inter-
preted in copy mode. For example, strings to start and end su-
perscripting could be defined like this
.ds { \v'-.3m'\s'\En[.s]*6u/10u'
.ds } \s0\v'.3m'
The use of \E ensures that these definitions work even if \*{
gets interpreted in copy mode (for example, by being used in a
macro argument).
\Ff
\F(fm
\F[fam]
Change font family. This is the same as the fam request. \F[]
switches back to the previous font family (note that \FP won't
work; it selects font family ‘P’ instead).
\mx
\m(xx
\m[xxx]
Set drawing color. \m[] switches back to the previous color.
\Mx
\M(xx
\M[xxx]
Set background color for filled objects drawn with the \D'...'
commands. \M[] switches back to the previous color.
\N'n' Typeset the glyph with index n in the current font. n can be
any integer. Most devices only have glyphs with indices between
0 and 255. If the current font does not contain a glyph with
that code, special fonts are not searched. The \N escape se-
quence can be conveniently used in conjunction with the char re-
quest, for example
.char \[phone] \f(ZD\N'37'
The index of each glyph is given in the fourth column in the
font description file after the charset command. It is possible
to include unnamed glyphs in the font description file by using
a name of ---; the \N escape sequence is the only way to use
these.
\On
\O[n] Suppress troff output. The escapes \O2, \O3, \O4, and \O5 are
intended for internal use by grohtml.
\O0 Disable any ditroff glyphs from being emitted to the de-
vice driver, provided that the escape occurs at the outer
level (see \O3 and \O4).
\O1 Enable output of glyphs, provided that the escape occurs
at the outer level.
\O0 and \O1 also reset the registers \n[opminx], \n[op-
miny], \n[opmaxx], and \n[opmaxy] to -1. These four reg-
isters mark the top left and bottom right hand corners of
a box which encompasses all written glyphs.
\O2 Provided that the escape occurs at the outer level, en-
able output of glyphs and also write out to stderr the
page number and four registers encompassing the glyphs
previously written since the last call to \O.
\O3 Begin a nesting level. At start-up, troff is at outer
level. This is really an internal mechanism for grohtml
while producing images. They are generated by running
the troff source through troff to the PostScript device
and ghostscript to produce images in PNG format. The \O3
escape starts a new page if the device is not html (to
reduce the possibility of images crossing a page bound-
ary).
\O4 End a nesting level.
\O5[Pfilename]
This escape is grohtml specific. Provided that this es-
cape occurs at the outer nesting level, write filename to
stderr. The position of the image, P, must be specified
and must be one of l, r, c, or i (left, right, centered,
inline). filename is associated with the production of
the next inline image.
\R'name ±n'
This has the same effect as
.nr name ±n
\s(nn
\s±(nn Set the point size to nn points; nn must be exactly two digits.
\s[±n]
\s±[n]
\s'±n'
\s±'n' Set the point size to n scaled points; n is a numeric expression
with a default scale indicator of z.
\Vx
\V(xx
\V[xxx]
Interpolate the contents of the environment variable xxx, as re-
turned by getenv(3). \V is interpreted in copy mode.
\Yx
\Y(xx
\Y[xxx]
This is approximately equivalent to \X'\*[xxx]'. However the
contents of the string or macro xxx are not interpreted; also it
is permitted for xxx to have been defined as a macro and thus
contain newlines (it is not permitted for the argument to \X to
contain newlines). The inclusion of newlines requires an exten-
sion to the Unix troff output format, and confuses drivers that
do not know about this extension.
\Z'anything'
Print anything and then restore the horizontal and vertical po-
sition; anything may not contain tabs or leaders.
\$0 The name by which the current macro was invoked. The als re-
quest can make a macro have more than one name.
\$* In a macro or string, the concatenation of all the arguments
separated by spaces.
\$@ In a macro or string, the concatenation of all the arguments
with each surrounded by double quotes, and separated by spaces.
\$^ In a macro, the representation of all parameters as if they were
an argument to the ds request.
\$(nn
\$[nnn]
In a macro or string, this gives the nn-th or nnn-th argument.
Macros and strings can have an unlimited number of arguments.
\?anything\?
When used in a diversion, this transparently embeds anything in
the diversion. anything is read in copy mode. When the diver-
sion is reread, anything is interpreted. anything may not con-
tain newlines; use \! if you want to embed newlines in a diver-
sion. The escape sequence \? is also recognized in copy mode
and turned into a single 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.
\/ This increases the width of the preceding glyph so that the
spacing between that glyph and the following glyph is correct if
the following glyph is a roman glyph. It is a good idea to use
this escape sequence whenever an italic glyph is immediately
followed by a roman glyph without any intervening space.
\, This modifies the spacing of the following glyph so that the
spacing between that glyph and the preceding glyph is correct if
the preceding glyph is a roman glyph. It is a good idea to use
this escape sequence whenever a roman glyph is immediately fol-
lowed by an italic glyph without any intervening space.
\) Like \& except that it behaves like a character declared with
the cflags request to be transparent for the purposes of end-of-
sentence recognition.
\~ This produces an unbreakable space that stretches like a normal
inter-word space when a line is adjusted.
\: This causes the insertion of a zero-width break point. It is
equal to \% within a word but without insertion of a soft hyphen
glyph.
\# Everything up to and including the next newline is ignored.
This is interpreted in copy mode. It is like \" except that \"
does not ignore the terminating newline.
New requests
.aln xx yy
Create an alias xx for number register object named yy. The new
name and the old name are exactly equivalent. If yy is unde-
fined, a warning of type reg is generated, and the request is
ignored.
.als xx yy
Create an alias xx for request, string, macro, or diversion ob-
ject named yy. The new name and the old name are exactly equiv-
alent (it is similar to a hard rather than a soft link). If yy
is undefined, a warning of type mac is generated, and the re-
quest is ignored. The de, am, di, da, ds, and as requests only
create a new object if the name of the macro, diversion or
string is currently undefined or if it is defined to be a re-
quest; normally they modify the value of an existing object.
.am1 xx yy
Similar to .am, but compatibility mode is switched off during
execution. To be more precise, a ‘compatibility save’ token is
inserted at the beginning of the macro addition, and a ‘compati-
bility restore’ token at the end. As a consequence, the re-
quests am, am1, de, and de1 can be intermixed freely since the
compatibility save/restore tokens only affect the macro parts
defined by .am1 and .ds1.
.ami xx yy
Append to macro indirectly. See the dei request below for more
information.
.ami1 xx yy
Same as the ami request but compatibility mode is switched off
during execution.
.as1 xx yy
Similar to .as, but compatibility mode is switched off during
expansion. To be more precise, a ‘compatibility save’ token is
inserted at the beginning of the string, and a ‘compatibility
restore’ token at the end. As a consequence, the requests as,
as1, ds, and ds1 can be intermixed freely since the compatibil-
ity save/restore tokens only affect the (sub)strings defined by
as1 and ds1.
.asciify xx
This request ‘unformats’ the diversion xx in such a way that
ASCII and space characters (and some escape sequences) that were
formatted and diverted into xx are treated like ordinary input
characters when xx is reread. Useful for diversions in conjunc-
tion with the writem request. It can be also used for gross
hacks; for example, this
.tr @.
.di x
@nr n 1
.br
.di
.tr @@
.asciify x
.x
sets register n to 1. Note that glyph information (font, font
size, etc.) is not preserved; use .unformat instead.
.backtrace
Print a backtrace of the input stack on stderr.
.blm xx
Set the blank line macro to xx. If there is a blank line macro,
it is invoked when a blank line is encountered instead of the
usual troff behaviour.
.box xx
.boxa xx
These requests are similar to the di and da requests with the
exception that a partially filled line does not become part of
the diversion (i.e., the diversion always starts with a new
line) but is restored after ending the diversion, discarding the
partially filled line which possibly comes from the diversion.
.break Break out of a while loop. See also the while and continue re-
quests. Be sure not to confuse this with the br request.
.brp This is the same as \p.
.cflags n c1 c2 ...
Characters c1, c2, ..., have properties determined by n, which
is ORed from the following:
1 The character ends sentences (initially characters .?!
have this property).
2 Lines can be broken before the character (initially no
characters have this property); a line is not broken at a
character with this property unless the characters on
each side both have non-zero hyphenation codes. This can
be overridden with value 64.
4 Lines can be broken after the character (initially char-
acters -\[hy]\[em] have this property); a line is not
broken at a character with this property unless the char-
acters on each side both have non-zero hyphenation codes.
This can be overridden with value 64.
8 The glyph associated with this character overlaps hori-
zontally (initially characters \[ul]\[rn]\[ru]\[radi-
calex]\[sqrtex] have this property).
16 The glyph associated with this character overlaps verti-
cally (initially glyph \[br] has this property).
32 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; in other
words the character is transparent for the purposes of
end-of-sentence recognition; this is the same as having a
zero space factor in TeX (initially characters
"')]*\[dg]\[rq]\[cq] have this property).
64 Ignore hyphenation code values of the surrounding charac-
ters. Use this in combination with values 2 and 4 (ini-
tially no characters have this property).
128 Prohibit a line break before the character, but allow a
line break after the character. This works only in com-
bination with flags 256 and 512 and has no effect other-
wise.
256 Prohibit a line break after the character, but allow a
line break before the character. This works only in com-
bination with flags 128 and 512 and has no effect other-
wise.
512 Allow line break before or after the character. This
works only in combination with flags 128 and 256 and has
no effect otherwise.
Contrary to flag values 2 and 4, the flags 128, 256, and 512
work pairwise. If, for example, the left character has value
512, and the right character 128, no line break gets inserted.
If we use value 6 instead for the left character, a line break
after the character can't be suppressed since the right neigh-
bour character doesn't get examined.
.char c string
[This request can both define characters and glyphs.]
Define entity c to be string. To be more precise, define (or
even override) a groff entity which can be accessed with name c
on the input side, and which uses string on the output side.
Every time glyph c needs to be printed, string is processed in a
temporary environment and the result is wrapped up into a single
object. Compatibility mode is turned off and the escape charac-
ter is set to \ while string is being processed. Any embolden-
ing, constant spacing or track kerning is applied to this object
rather than to individual glyphs in string.
A groff object defined by this request can be used just like a
normal glyph provided by the output device. In particular other
characters can be translated to it with the tr request; it can
be made the leader glyph by the lc request; repeated patterns
can be drawn with the glyph using the \l and \L escape se-
quences; words containing c can be hyphenated correctly, if the
hcode request is used to give the object a hyphenation code.
There is a special anti-recursion feature: Use of glyph within
the glyph's definition is handled like normal glyphs not defined
with char.
A glyph definition can be removed with the rchar request.
.chop xx
Chop the last element off macro, string, or diversion xx. This
is useful for removing the newline from the end of diversions
that are to be interpolated as strings.
.class name c1 c2 ...
Assign name to a set of characters c1, c2, ..., so that they can
be referred to from other requests easily (currently .cflags
only). Character ranges (indicated by an intermediate ‘-’) and
nested classes are possible also. This is useful to assign
properties to a large set of characters.
.close stream
Close the stream named stream; stream will no longer be an ac-
ceptable argument to the write request. See the open request.
.composite glyph1 glyph2
Map glyph name glyph1 to glyph name glyph2 if it is used in
\[...] with more than one component.
.continue
Finish the current iteration of a while loop. See also the
while and break requests.
.color n
If n is non-zero or missing, enable colors (this is the de-
fault), otherwise disable them.
.cp n If n is non-zero or missing, enable compatibility mode, other-
wise disable it. In compatibility mode, long names are not rec-
ognized, and the incompatibilities caused by long names do not
arise.
.defcolor xxx scheme color_components
Define color xxx. scheme can be one of the following values:
rgb (three components), cmy (three components), cmyk (four com-
ponents), and gray or grey (one component). Color components
can be given either as a hexadecimal string or as positive deci-
mal integers in the range 0–65535. A hexadecimal string con-
tains all color components concatenated; it must start with ei-
ther # or ##. The former specifies hex values in the range
0–255 (which are internally multiplied by 257), the latter in
the range 0–65535. Examples: #FFC0CB (pink), ##ffff0000ffff
(magenta). A new scaling indicator f has been introduced which
multiplies its value by 65536; this makes it convenient to spec-
ify color components as fractions in the range 0 to 1. Example:
.defcolor darkgreen rgb 0.1f 0.5f 0.2f
Note that f is the default scaling indicator for the defcolor
request, thus the above statement is equivalent to
.defcolor darkgreen rgb 0.1 0.5 0.2
The color named default (which is device-specific) can't be re-
defined. It is possible that the default color for \M and \m is
not the same.
.de1 xx yy
Similar to .de, but compatibility mode is switched off during
execution. On entry, the current compatibility mode is saved
and restored at exit.
.dei xx yy
Define macro indirectly. The following example
.ds xx aa
.ds yy bb
.dei xx yy
is equivalent to
.de aa bb
.dei1 xx yy
Similar to the dei request but compatibility mode is switched
off during execution.
.device anything
This is (almost) the same as the \X escape. anything is read in
copy mode; a leading " is stripped.
.devicem xx
This is the same as the \Y escape (to embed the contents of a
macro into the intermediate output preceded with ‘x X’).
.do xxx
Interpret .xxx with compatibility mode disabled. For example,
.do fam T
would have the same effect as
.fam T
except that it would work even if compatibility mode had been
enabled. Note that the previous compatibility mode is restored
before any files sourced by xxx are interpreted.
.ds1 xx yy
Similar to .ds, but compatibility mode is switched off during
expansion. To be more precise, a ‘compatibility save’ token is
inserted at the beginning of the string, and a ‘compatibility
restore’ token at the end.
.ecs Save current escape character.
.ecr Restore escape character saved with ecs. Without a previous
call to ecs, ‘\’ will be the new escape character.
.evc xx
Copy the contents of environment xx to the current environment.
No pushing or popping of environments is done.
.fam xx
Set the current font family to xx. The current font family is
part of the current environment. If xx is missing, switch back
to previous font family. The value at start-up is ‘T’. See the
description of the sty request for more information on font fam-
ilies.
.fchar c string
Define fallback character (or glyph) c to be string. The syntax
of this request is the same as the char request; the only dif-
ference is that a glyph defined with char hides the glyph with
the same name in the current font, whereas a glyph defined with
fchar is checked only if the particular glyph isn't found in the
current font. This test happens before checking special fonts.
.fcolor c
Set the fill color to c. If c is missing, switch to the previ-
ous fill color.
.fschar f c string
Define fallback character (or glyph) c for font f to be string.
The syntax of this request is the same as the char request (with
an additional argument to specify the font); a glyph defined
with fschar is searched after the list of fonts declared with
the fspecial request but before the list of fonts declared with
.special.
.fspecial f s1 s2 ...
When the current font is f, fonts s1, s2, ..., are special, that
is, they are searched for glyphs not in the current font. Any
fonts specified in the special request are searched after fonts
specified in the fspecial request. Without argument, reset the
list of global special fonts to be empty.
.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 operators,
or in the ft, ul, bd, cs, tkf, special, fspecial, fp, or sty re-
quests, font g is used. If g is missing, or equal to f then
font f is not translated.
.fzoom f zoom
Set zoom factor zoom for font f. zoom must a non-negative inte-
ger 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
real font name, not a style.
.gcolor c
Set the glyph color to c. If c is missing, switch to the previ-
ous glyph color.
.hcode c1 code1 c2 code2 ...
Set the hyphenation code of character c1 to code1 and that of c2
to code2, and so on. A hyphenation code must be a single input
character (not a special character) other than a digit or a
space. Initially each lower-case letter a–z has a hyphenation
code, which is itself, and each upper-case letter A–Z has a hy-
phenation code which is the lower-case version of itself. See
also the hpf request.
.hla lang
Set the current hyphenation language to lang. Hyphenation ex-
ceptions specified with the hw request and hyphenation patterns
specified with the hpf request are both associated with the cur-
rent hyphenation language. The hla request is usually invoked
by the troffrc file to set up a default language.
.hlm n Set the maximum number of consecutive hyphenated lines to n. If
n is negative, there is no maximum. The default value is -1.
This value is associated with the current environment. Only
lines output from an environment count towards the maximum asso-
ciated with that environment. Hyphens resulting from \% are
counted; explicit hyphens are not.
.hpf file
Read hyphenation patterns from file; this is searched for in the
same way that name.tmac is searched for when the -mname option
is specified. It should have the same format as (simple) TeX
patterns files. More specifically, 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.
• No support for ‘digraphs’ like \$.
• ^^xx (x is 0–9 or a–f) and ^^x (character code of x in
the range 0–127) are recognized; other use of ^ causes an
error.
• No macro expansion.
• hpf checks for the expression \patterns{...} (possibly
with whitespace before and 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
(only recognizing the % character as the start of a com-
ment).
Use the hpfcode request to map the encoding used in hyphenation
patterns files to groff's input encoding. By default, every-
thing maps to itself except letters ‘A’ to ‘Z’ which map to ‘a’
to ‘z’.
The set of hyphenation patterns is associated with the current
language set by the hla request. The hpf request is usually in-
voked by the troffrc file; a second call replaces the old pat-
terns with the new ones.
.hpfa file
The same as hpf except that the hyphenation patterns from file
are appended to the patterns already loaded in the current lan-
guage.
.hpfcode a b c d ...
After reading a hyphenation patterns file with the hpf or hpfa
request, convert all characters with character code a in the re-
cently read patterns to character code b, character code c to d,
etc. Initially, all character codes map to themselves. The ar-
guments of hpfcode must be integers in the range 0 to 255. Note
that it is even possible to use character codes which are in-
valid in groff otherwise.
.hym n Set the hyphenation margin to n: when the current adjustment
mode is not b, the line is not hyphenated if the line is no more
than n short. The default hyphenation margin is 0. The default
scaling indicator for this request is m. The hyphenation margin
is associated with the current environment. The current hyphen-
ation margin is available in the \n[.hym] register.
.hys n Set the hyphenation space to n: When the current adjustment mode
is b don't hyphenate the line if the line can be justified by
adding no more than n extra space to each word space. The de-
fault hyphenation space is 0. The default scaling indicator for
this request is m. The hyphenation space is associated with the
current environment. The current hyphenation space is available
in the \n[.hys] register.
.itc n macro
Variant of .it for which a line interrupted with \c is not
counted as an input line.
.kern n
If n is non-zero or missing, enable pairwise kerning, otherwise
disable it.
.length xx string
Compute the length of string and return it in the number regis-
ter xx (which is not necessarily defined before).
.linetabs n
If n is non-zero or missing, enable line-tabs mode, otherwise
disable it (which is the default). In line-tabs mode, tab dis-
tances are computed relative to the (current) output line. Oth-
erwise they are taken relative to the input line. 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
In line-tabs mode, the same code gives
a b c
Line-tabs mode is associated with the current environment; the
read-only number register \n[.linetabs] is set to 1 if in line-
tabs mode, and 0 otherwise.
.lsm xx
Set the leading spaces macro to xx. If there are leading spaces
in an input line, it is invoked instead of the usual troff be-
haviour; the leading spaces are removed. Registers \n[lsn] and
\n[lss] hold the number of removed leading spaces and the corre-
sponding horizontal space, respectively.
.mso file
The same as the so request except that file is searched for in
the same directories as macro files for the -m command-line op-
tion. If the file name to be included has the form name.tmac
and it isn't found, mso tries to include tmac.name instead and
vice versa. A warning of type file is generated if file can't
be loaded, and the request is ignored.
.nop anything
Execute anything. This is similar to ‘.if 1’.
.nroff Make the n built-in condition true and the t built-in condition
false. This can be reversed using the troff request.
.open stream filename
Open filename for writing and associate the stream named stream
with it. See also the close and write requests.
.opena stream filename
Like open, but if filename exists, append to it instead of trun-
cating it.
.output string
Emit string directly to the intermediate output (subject to
copy-mode interpretation); this is similar to \! used at the top
level. An initial double quote in string is stripped off to al-
low initial blanks.
.pev Print the current environment and each defined environment state
on stderr.
.pnr Print the names and contents of all currently defined number
registers on stderr.
.psbb filename
Get the bounding box of a PostScript image filename. This file
must conform to Adobe's Document Structuring Conventions; the
command looks for a %%BoundingBox comment to extract the bound-
ing box values. After a successful call, the coordinates (in
PostScript units) of the lower left and upper right corner can
be found in the registers \n[llx], \n[lly], \n[urx], and
\n[ury], respectively. If some error has occurred, the four
registers are set to zero.
.pso command
This behaves like the so request except that input comes from
the standard output of command.
.ptr Print the names and positions of all traps (not including input
line traps and diversion traps) on stderr. Empty slots in the
page trap list are printed as well, because they can affect the
priority of subsequently planted traps.
.pvs ±n
Set the post-vertical line space to n; default scale indicator
is p. This value is added to each line after it has been out-
put. With no argument, the post-vertical line space is set to
its previous value.
The total vertical line spacing consists of four components: .vs
and \x with a negative value which are applied before the line
is output, and .pvs and \x with a positive value which are ap-
plied after the line is output.
.rchar c1 c2 ...
Remove the definitions of glyphs c1, c2, ... This undoes the
effect of a char request.
.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 c1 c2 ...
Remove the font-specific definitions of glyphs c1, c2, ... This
undoes the effect of an fschar request.
.rj
.rj n Right justify the next n input lines. Without an argument right
justify the next input line. The number of lines to be right
justified is available in the \n[.rj] register. This implicitly
does .ce 0. The ce request implicitly does .rj 0.
.rnn xx yy
Rename number register xx to yy.
.schar c string
Define global fallback character (or glyph) c to be string. The
syntax of this request is the same as the char request; a glyph
defined with schar is searched after the list of fonts declared
with the special request but before the mounted special fonts.
.shc c Set the soft hyphen character to c. If c is omitted, the soft
hyphen character is set to the default \[hy]. The soft hyphen
character is the glyph which is inserted when a word is hyphen-
ated at a line break. If the soft hyphen character does not ex-
ist in the font of the glyph immediately preceding a potential
break point, then the line is not broken at that point. Neither
definitions (specified with the char request) nor translations
(specified with the tr request) are considered when finding the
soft hyphen character.
.shift n
In a macro, shift the arguments by n positions: argument i be-
comes argument i-n; arguments 1 to n are no longer available.
If n is missing, arguments are shifted by 1. Shifting by nega-
tive amounts is currently undefined.
.sizes s1 s2 ... sn [0]
This command is similar to the sizes command of a DESC file. It
sets the available font sizes for the current font to s1, s2,
..., sn scaled points. The list of sizes can be terminated by
an optional 0. Each si can also be a range of sizes m–n. Con-
trary to the font file command, the list can't extend over more
than a single line.
.special s1 s2 ...
Fonts s1, s2, ..., are special and are searched for glyphs not
in the current font. Without arguments, reset the list of spe-
cial fonts to be empty.
.spreadwarn limit
Make troff emit a warning if the additional space inserted for
each space between words in an output line is larger or equal to
limit. A negative value is changed to zero; no argument toggles
the warning on and off without changing limit. The default
scaling indicator is m. At startup, spreadwarn is deactivated,
and limit is set to 3m. For example, .spreadwarn 0.2m causes a
warning if troff must add 0.2m or more for each interword space
in a line. This request is active only if text is justified to
both margins (using .ad b).
.sty n f
Associate style f with font position n. A font position can be
associated either with a font or with a style. The current font
is the index of a font position and so is also either a font or
a style. When it is a style, the font that is actually used is
the font the name of which is the concatenation of the name of
the current family and the name of the current style. For exam-
ple, if the current font is 1 and font position 1 is associated
with style R and the current font family is T, then font TR is
used. If the current font is not a style, then the current fam-
ily is ignored. When the requests cs, bd, tkf, uf, or fspecial
are applied to a style, then they are applied instead to the
member of the current family corresponding to that style. The
default family can be set with the -f command-line option. The
styles command in the DESC file controls which font positions
(if any) are initially associated with styles rather than fonts.
.substring xx n1 [n2]
Replace the string named xx with the substring defined by the
indices n1 and n2. The first character in the string has in-
dex 0. If n2 is omitted, it is taken to be equal to the
string's length. If the index value n1 or n2 is negative, it is
counted from the end of the string, going backwards: The last
character has index -1, the character before the last character
has index -2, etc.
.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 point 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 point 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 point size.
.tm1 string
Similar to the tm request, string is read in copy mode and writ-
ten on the standard error, but an initial double quote in string
is stripped off to allow initial blanks.
.tmc string
Similar to tm1 but without writing a final newline.
.trf filename
Transparently output the contents of file filename. Each line
is output as if preceded by \!; however, the lines are not sub-
ject to copy-mode interpretation. If the file does not end with
a newline, then a newline is added. For example, you can define
a macro x containing the contents of file f, using
.di x
.trf f
.di
Unlike with the cf request, the file cannot contain characters,
such as NUL, that are not valid troff input characters.
.trin abcd
This is the same as the tr request except that the asciify re-
quest 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 di-
version 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 n built-in condition false, and the t built-in condi-
tion true. This undoes the effect of the nroff request.
.unformat xx
This request ‘unformats’ the diversion xx. Contrary to the
asciify request, which tries to convert formatted elements of
the diversion back to input tokens as much as possible, .unfor-
mat only handles tabs and spaces between words (usually caused
by spaces or newlines in the input) specially. The former are
treated as if they were input tokens, and the latter are
stretchable again. Note that the vertical size of lines is not
preserved. Glyph information (font, font size, space width,
etc.) is retained. Useful in conjunction with the box and boxa
requests.
.vpt n Enable vertical position traps if n is non-zero, disable them
otherwise. Vertical position traps are traps set by the wh or
dt requests. Traps set by the it request are not vertical posi-
tion traps. The parameter that controls whether vertical posi-
tion traps are enabled is global. Initially vertical position
traps are enabled.
.warn n
Control warnings. n is the sum of the numbers associated with
each warning that is to be enabled; all other warnings are dis-
abled. The number associated with each warning is listed in
troff(1). For example, .warn 0 disables all warnings, and
.warn 1 disables all warnings except that about missing glyphs.
If n is not given, all warnings are enabled.
.warnscale si
Set the scaling indicator used in warnings to si. Valid values
for si are u, i, c, p, and P. At startup, it is set to i.
.while c anything
While condition c is true, accept anything as input; c can be
any condition acceptable to an if request; anything can comprise
multiple lines if the first line starts with \{ and the last
line ends with \}. See also the break and continue requests.
.write stream anything
Write anything to the stream named stream. stream must previ-
ously have been the subject of an open request. anything is
read in copy mode; a leading " is stripped.
.writec stream anything
Similar to write but without writing a final newline.
.writem stream xx
Write the contents of the macro or string xx to the stream named
stream. stream must previously have been the subject of an open
request. xx is read in copy mode.
Extended escape sequences
\D'...'
All drawing commands of groff's intermediate output are ac-
cepted. See subsection “Drawing Commands” below.
Extended requests
.cf filename
When used in a diversion, this embeds in the diversion an object
which, when reread, will cause the contents of filename to be
transparently copied through to the output. In Unix troff, the
contents of filename is immediately copied through to the output
regardless of whether there is a current diversion; this behav-
iour is so anomalous that it must be considered a bug.
.de xx yy
.am xx yy
.ds xx yy
.as xx yy
In compatibility mode, these requests behaves similar to .de1,
.am1, .ds1, and .as1, respectively: A ‘compatibility save’ token
is inserted at the beginning, and a ‘compatibility restore’ to-
ken at the end, with compatibility mode switched on during exe-
cution.
.ev xx If xx is not a number, this switches to a named environment
called xx. The environment should be popped with a matching ev
request without any arguments, just as for numbered environ-
ments. There is no limit on the number of named environments;
they are created the first time that they are referenced.
.hy n New additive values 16 and 32 are available; the former enables
hyphenation before the last character, the latter enables hy-
phenation after the first character.
.ss m n
When two arguments are given to the ss request, the second argu-
ment gives the sentence space size. If the second argument is
not given, the sentence space size is the same as the word space
size. Like the word space size, the sentence space is in units
of one twelfth of the spacewidth parameter for the current font.
Initially both the word space size and the sentence space size
are 12. Contrary to Unix troff, GNU troff handles this request
in nroff mode also; a given value is then rounded down to the
nearest multiple of 12. The sentence space size is used in two
circumstances. If the end of a sentence occurs at the end of a
line in fill mode, then both an inter-word space and a sentence
space are added; if two spaces follow the end of a sentence in
the middle of a line, then the second space is a sentence space.
Note that the behaviour of Unix troff is exactly that exhibited
by GNU troff if a second argument is never given to the ss re-
quest. In GNU troff, as in Unix troff, you should always follow
a sentence with either a newline or two spaces.
.ta n1 n2 ... nn T r1 r2 ... rn
Set tabs at positions n1, n2, ..., nn and then set tabs at
nn+r1, nn+r2, ..., nn+rn and then at nn+rn+r1, nn+rn+r2, ...,
nn+rn+rn, and so on. For example,
.ta T .5i
sets tabs every half an inch.
New number registers
The following read-only registers are available:
\n[.br]
Within a macro call, it is set to 1 if the macro is called with
the ‘normal’ control character (‘.’ by default), and set to 0
otherwise. This allows the reliable modification of requests.
.als bp*orig bp
.de bp
.tm before bp
.ie \\n[.br] .bp*orig
.el 'bp*orig
.tm after bp
..
Using this register outside of a macro makes no sense (it always
returns zero in such cases).
\n[.C] 1 if compatibility mode is in effect, 0 otherwise.
\n[.cdp]
The depth of the last glyph added to the current environment.
It is positive if the glyph extends below the baseline.
\n[.ce]
The number of lines remaining to be centered, as set by the ce
request.
\n[.cht]
The height of the last glyph added to the current environment.
It is positive if the glyph extends above the baseline.
\n[.color]
1 if colors are enabled, 0 otherwise.
\n[.csk]
The skew of the last glyph added to the current environment.
The skew of a glyph is how far to the right of the center of a
glyph the center of an accent over that glyph should be placed.
\n[.ev]
The name or number of the current environment. This is a
string-valued register.
\n[.fam]
The current font family. This is a string-valued register.
\n[.fn]
The current (internal) real font name. This is a string-valued
register. If the current font is a style, the value of \n[.fn]
is the proper concatenation of family and style name.
\n[.fp]
The number of the next free font position.
\n[.g] Always 1. Macros should use this to determine whether they are
running under GNU troff.
\n[.height]
The current height of the font as set with \H.
\n[.hla]
The current hyphenation language as set by the hla request.
\n[.hlc]
The number of immediately preceding consecutive hyphenated
lines.
\n[.hlm]
The maximum allowed number of consecutive hyphenated lines, as
set by the hlm request.
\n[.hy]
The current hyphenation flags (as set by the hy request).
\n[.hym]
The current hyphenation margin (as set by the hym request).
\n[.hys]
The current hyphenation space (as set by the hys request).
\n[.in]
The indentation that applies to the current output line.
\n[.int]
Set to a positive value if last output line is interrupted
(i.e., if it contains \c).
\n[.kern]
1 if pairwise kerning is enabled, 0 otherwise.
\n[.lg]
The current ligature mode (as set by the lg request).
\n[.linetabs]
The current line-tabs mode (as set by the linetabs request).
\n[.ll]
The line length that applies to the current output line.
\n[.lt]
The title length as set by the lt request.
\n[.m] The name of the current drawing color. This is a string-valued
register.
\n[.M] The name of the current background color. This is a string-val-
ued register.
\n[.ne]
The amount of space that was needed in the last ne request that
caused a trap to be sprung. Useful in conjunction with the
\n[.trunc] register.
\n[.ns]
1 if no-space mode is active, 0 otherwise.
\n[.O] The current output level as set with \O.
\n[.P] 1 if the current page is in the output list set with -o.
\n[.pe]
1 during a page ejection caused by the bp request, 0 otherwise.
\n[.pn]
The number of the next page, either the value set by a pn re-
quest, or the number of the current page plus 1.
\n[.ps]
The current point size in scaled points.
\n[.psr]
The last-requested point size in scaled points.
\n[.pvs]
The current post-vertical line space as set with the pvs re-
quest.
\n[.rj]
The number of lines to be right-justified as set by the rj re-
quest.
\n[.slant]
The slant of the current font as set with \S.
\n[.sr]
The last requested point size in points as a decimal fraction.
This is a string-valued register.
\n[.ss]
\n[.sss]
These give the values of the parameters set by the first and
second arguments of the ss request.
\n[.sty]
The current font style. This is a string-valued register.
\n[.tabs]
A string representation of the current tab settings suitable for
use as an argument to the ta request.
\n[.trunc]
The amount of vertical space truncated by the most recently
sprung vertical position 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, it
represents the difference of what the vertical position would
have been but for the trap, and what the vertical position actu-
ally is. Useful in conjunction with the \n[.ne] register.
\n[.U] Set to 1 if in safer mode and to 0 if in unsafe mode (as given
with the -U command-line option).
\n[.vpt]
1 if vertical position traps are enabled, 0 otherwise.
\n[.warn]
The sum of the numbers associated with each of the currently en-
abled warnings. The number associated with each warning is
listed in troff(1).
\n[.x] The major version number. For example, if the version number is
1.03, then \n[.x] contains 1.
\n[.y] The minor version number. For example, if the version number is
1.03, then \n[.y] contains 03.
\n[.Y] The revision number of groff.
\n[.zoom]
The zoom value of the current font, in multiples of 1/1000th.
Zero if no magnification.
\n[llx]
\n[lly]
\n[urx]
\n[ury]
These four read/write registers are set by the psbb request and
contain the bounding box values (in PostScript units) of a given
PostScript image.
The following read/write registers are set by the \w escape sequence:
\n[rst]
\n[rsb]
Like the st and sb registers, but take account of the heights
and depths of glyphs.
\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 argu-
ment, the center of an accent from a roman font should be placed
over that glyph.
Other available read/write number registers are:
\n[c.] The current input line number. \n[.c] is a read-only alias to
this register.
\n[hours]
The number of hours past midnight. Initialized at start-up.
\n[hp] The current horizontal position at input line.
\n[lsn]
\n[lss]
If there are leading spaces in an input line, these registers
hold the number of leading spaces and the corresponding horizon-
tal space, respectively.
\n[minutes]
The number of minutes after the hour. Initialized at start-up.
\n[seconds]
The number of seconds after the minute. Initialized at start-
up.
\n[systat]
The return value of the system() function executed by the last
sy request.
\n[slimit]
If greater than 0, the maximum number of objects on the input
stack. If less than or equal to 0, there is no limit on the
number of objects on the input stack. With no limit, recursion
can continue until virtual memory is exhausted.
\n[year]
The current year. Note that the traditional troff number regis-
ter \n[yr] is the current year minus 1900.
Miscellaneous
troff predefines a single (read/write) string-based register, \*[.T],
which contains the argument given to the -T command-line option, namely
the current output device (for example, latin1 or ascii). Note that
this is not the same as the (read-only) number register \n[.T] which is
defined to be 1 if troff is called with the -T command-line option, and
zero otherwise. This behaviour is different from Unix troff.
Fonts not listed in the DESC file are automatically mounted on the next
available font position when they are referenced. If a font is to be
mounted explicitly with the fp request on an unused font position, it
should be mounted on the first unused font position, which can be found
in the \n[.fp] register; although troff does not enforce this strictly,
it does not allow a font to be mounted at a position whose number is
much greater than that of any currently used position.
Interpolating a string does not hide existing macro arguments. Thus in
a macro, a more efficient way of doing
.xx \\$@
is
\\*[xx]\\
If the font description file contains pairwise kerning information,
glyphs from that font are kerned. Kerning between two glyphs can be
inhibited by placing a \& between them.
In a string comparison in a condition, characters that appear at dif-
ferent input levels to the first delimiter character are not recognized
as the second or third delimiters. This applies also to the tl re-
quest. In a \w escape sequence, a character that appears at a differ-
ent input level to the starting delimiter character is not recognized
as the closing delimiter character. The same is true for \A, \b, \B,
\C, \l, \L, \o, \X, and \Z. When decoding a macro or string argument
that is delimited by double quotes, a character that appears at a dif-
ferent input level to the starting delimiter character is not recog-
nized as the closing delimiter character. The implementation of \$@
ensures that the double quotes surrounding an argument appear at the
same input level, which is different to the input level of the argument
itself. In a long escape name ] is not recognized as a closing delim-
iter except when it occurs at the same input level as the opening [.
In compatibility mode, no attention is paid to the input-level.
There are some new types of condition:
.if rxxx
True if there is a number register named xxx.
.if dxxx
True if there is a string, macro, diversion, or request named
xxx.
.if mxxx
True if there is a color named xxx.
.if cch
True if there is a character (or glyph) ch available; ch is ei-
ther an ASCII character or a glyph (special character) \N'xxx',
\(xx or \[xxx]; the condition is also true if ch has been de-
fined by the char request.
.if Ff True if font f exists. f is handled as if it was opened with
the ft request (this is, font translation and styles are ap-
plied), without actually mounting it.
.if Ss True if style s has been registered. Font translation is ap-
plied.
The tr request can now map characters onto \~.
The space width emitted by the \| and \^ escape sequences can be con-
trolled on a per-font basis. If there is a glyph named \| or \^, re-
spectively (note the leading backslash), defined in the current font
file, use this glyph's width instead of the default value.
It is now possible to have whitespace between the first and second dot
(or the name of the ending macro) to end a macro definition. Example:
.if t \{\
. de bar
. nop Hello, I'm ‘bar’.
. .
.\}
INTERMEDIATE OUTPUT FORMAT
This section describes the format output by GNU troff. The output for-
mat used by GNU troff is very similar to that used by Unix device-inde-
pendent troff. Only the differences are documented here.
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 Height command is also in scaled points.
Text Commands
Nn Print glyph with index n (a non-negative integer) of the current
font.
If the tcommand line is present in the DESC file, troff uses the fol-
lowing two commands.
txxx xxx is any sequence of characters terminated by a space or a
newline (to be more precise, it is a sequence of glyphs which
are accessed with the corresponding characters); the first char-
acter should be printed at the current position, the current
horizontal position should be increased by the width of the
first character, and so on for each character. The width of the
glyph is that given in the font file, appropriately scaled for
the current point size, and rounded so that it is a multiple of
the horizontal resolution. Special characters cannot be printed
using this command.
un xxx This is same as the t command except that after printing each
character, the current horizontal position is increased by the
sum of the width of that character and n.
Note that single characters can have the eighth bit set, as can the
names of fonts and special characters.
The names of glyphs and fonts can be of arbitrary length; drivers
should not assume that they are only two characters long.
When a glyph is to be printed, that glyph is always in the current
font. Unlike device-independent troff, it is not necessary for drivers
to search special fonts to find a glyph.
For color support, some new commands have been added:
mc cyan magenta yellow
md
mg gray
mk cyan magenta yellow black
mr red green blue
Set the color components of the current drawing color, using
various color schemes. md resets the drawing color to the de-
fault value. The arguments are integers in the range 0 to
65536.
The x device control command has been extended.
x u n If n is 1, start underlining of spaces. If n is 0, stop under-
lining of spaces. This is needed for the cu request in nroff
mode and is ignored otherwise.
Drawing Commands
The D drawing command has been extended. These extensions are not used
by GNU pic if the -n option is given.
Df n\n Set the shade of gray to be used for filling solid objects to n;
n must be an integer between 0 and 1000, where 0 corresponds
solid white and 1000 to solid black, and values in between cor-
respond to intermediate shades of gray. This applies only to
solid circles, solid ellipses and solid polygons. By default, a
level of 1000 is used. Whatever color a solid object has, it
should completely obscure everything beneath it. A value
greater than 1000 or less than 0 can also be used: this means
fill with the shade of gray that is currently being used for
lines and text. Normally this is black, but some drivers may
provide a way of changing this.
The corresponding \D'f...' command shouldn't be used since its
argument is always rounded to an integer multiple of the hori-
zontal resolution which can lead to surprising results.
DC d\n Draw a solid circle with a diameter of d with the leftmost point
at the current position.
DE dx dy\n
Draw a solid ellipse with a horizontal diameter of dx and a ver-
tical diameter of dy with the leftmost point at the current po-
sition.
Dp dx1 dy1 dx2 dy2 ... .lf 3501
dxn dyn\n Draw a polygon with, for i=1,...,n+1, the i-th vertex
at the current position +jΣ1(dxj,dyj). At the moment, GNU pic
only uses this command to generate triangles and rectangles.
DP dx1 dy1 dx2 dy2 ... .lf 3513
dxn dyn\n Like Dp but draw a solid rather than outlined polygon.
Dt n\n Set the current line thickness to n machine units. Tradition-
ally Unix troff drivers use a line thickness proportional to the
current point size; drivers should continue to do this if no Dt
command has been given, or if a Dt command has been given with a
negative value of n. A zero value of n selects the smallest
available line thickness.
A difficulty arises in how the current position should be changed after
the execution of these commands. This is not of great importance since
the code generated by GNU pic does not depend on this. Given a drawing
command of the form
\D'c x1 y1 x2 y2 ... .lf 3546 xn yn'
where c is not one of c, e, l, a, or ~, Unix troff treats each of the
xi as a horizontal quantity, and each of the yi as a vertical quantity
and assumes that the width of the drawn object is iΣ1xi, and that the
height is iΣ1yi. (The assumption about the height can be seen by exam-
ining the st and sb registers after using such a D command in a \w es-
cape sequence). This rule also holds for all the original drawing com-
mands with the exception of De. For the sake of compatibility GNU
troff also follows this rule, even though it produces an ugly result in
the case of the Dt and Df, and, to a lesser extent, DE commands. Thus
after executing a D command of the form
Dc x1 y1 x2 y2 ... .lf 3590 xn yn\n
the current position should be increased by (iΣ1xi,iΣ1yi).
Another set of extensions is
DFc cyan magenta yellow\n
DFd\n
DFg gray\n
DFk cyan magenta yellow black\n
DFr red green blue\n
Set the color components of the filling color similar to the
m commands above.
The current position isn't changed by those colour commands (contrary
to Df).
Device Control Commands
There is a continuation convention which permits the argument to the
x X command to contain newlines: when outputting the argument to the
x X command, GNU troff follows each newline in the argument with a +
character (as usual, it terminates the entire argument with a newline);
thus if the line after the line containing the x X command starts with
+, then the newline ending the line containing the x X command should
be treated as part of the argument to the x X command, the + should be
ignored, and the part of the line following the + should be treated
like the part of the line following the x X command.
The first three output commands are guaranteed to be:
x T device
x res n h v
x init
INCOMPATIBILITIES
In spite of the many extensions, groff has retained compatibility to
classical troff to a large degree. For the cases where the extensions
lead to collisions, a special compatibility mode with the restricted,
old functionality was created for groff.
Groff Language
groff provides a compatibility mode that allows the processing of roff
code written for classical troff or for other implementations of roff
in a consistent way.
Compatibility mode can be turned on with the -C command-line option,
and turned on or off with the .cp request. The number register \n(.C
is 1 if compatibility mode is on, 0 otherwise.
This became necessary because the GNU concept for long names causes
some incompatibilities. Classical troff interprets
.dsabcd
as defining a string ab with contents cd. In groff mode, this is con-
sidered as a call of a macro named dsabcd.
Also classical troff interprets \*[ or \n[ as references to a string or
number register called [ while groff takes this as the start of a long
name.
In compatibility mode, groff interprets these things in the traditional
way; so long names are not recognized.
On the other hand, groff in GNU native mode does not allow to use the
single-character escapes \\ (backslash), \| (vertical bar), \^ (caret),
\& (ampersand), \{ (opening brace), \} (closing brace), ‘\ ’ (space),
\' (single quote), \` (backquote), \- (minus), \_ (underline), \!
(bang), \% (percent), and \c (character c) in names of strings, macros,
diversions, number registers, fonts or environments, whereas classical
troff does.
The \A escape sequence can be helpful in avoiding these escape se-
quences in names.
Fractional point sizes cause one noteworthy incompatibility. In clas-
sical troff, the ps request ignores scale indicators and so
.ps 10u
sets the point size to 10 points, whereas in groff native mode the
point size is set to 10 scaled points.
In groff, there is a fundamental difference between unformatted input
characters, and formatted output characters (glyphs). Everything that
affects how a glyph is output is stored with the glyph; once a glyph
has been constructed it is unaffected by any subsequent requests that
are executed, including the bd, cs, tkf, tr, or fp requests.
Normally glyphs are constructed from input characters at the moment im-
mediately before the glyph is added to the current output line.
Macros, diversions and strings are all, in fact, the same type of ob-
ject; they contain lists of input characters and glyphs in any combina-
tion.
Special characters can be both; before being added to the output, they
act as input entities, afterwards they denote glyphs.
A glyph does not behave like an input character for the purposes of
macro processing; it does not inherit any of the special properties
that the input character from which it was constructed might have had.
The following example makes things clearer.
.di x
\\\\
.br
.di
.x
With GNU troff this is printed as \\. So each pair of input back-
slashes ‘\\’ is turned into a single output backslash glyph ‘\’ and the
resulting output backslashes are not interpreted as escape characters
when they are reread.
Classical troff would interpret them as escape characters when they
were reread and would end up printing a single backslash ‘\’.
In GNU, the correct way to get a printable version of the backslash
character ’\’ is the \(rs escape sequence, but classical troff does not
provide a clean feature for getting a non-syntactical backslash. A
close method is the printable version of the current escape character
using the \e escape sequence; this works if the current escape charac-
ter is not redefined. It works in both GNU mode and compatibility
mode, while dirty tricks like specifying a sequence of multiple back-
slashes do not work reliably; for the different handling in diversions,
macro definitions, or text mode quickly leads to a confusion about the
necessary number of backslashes.
To store an escape sequence in a diversion that is interpreted when the
diversion is reread, either the traditional \! transparent output fa-
cility or the new \? escape sequence can be used.
Intermediate Output
The groff intermediate output format is in a state of evolution. So
far it has some incompatibilities, but it is intended to establish a
full compatibility to the classical troff output format. Actually the
following incompatibilities exist:
• The positioning after the drawing of the polygons conflicts with the
classical definition.
• The intermediate output cannot be rescaled to other devices as clas-
sical ‘device-independent’ troff did.
AUTHORS
This document was written by James Clark ⟨jjc@jclark.com⟩ and modified
by Werner Lemberg ⟨wl@gnu.org⟩ and Bernd Warken ⟨groff-bernd.warken-72@
web.de⟩.
SEE ALSO
Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner
Lemberg, is the primary groff manual. You can browse it interactively
with “info groff”.
groff(1)
A list of all documentation around groff.
groff(7)
A description of the groff language, including a short, but com-
plete reference of all predefined requests, registers, and es-
capes of plain groff. From the command line, this is called us-
ing
man 7 groff
roff(7)
A survey of roff systems, including pointers to further histori-
cal documentation.
[CSTR #54]
The Nroff/Troff User's Manual by J. F. Ossanna of 1976 in the
revision of Brian Kernighan of 1992, being the classical troff
documentation ⟨http://cm.bell-labs.com/cm/cs/cstr/54.ps.gz⟩.
groff 1.22.4 7 March 2023 GROFF_DIFF(7)
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