Ubuntu Manpage: groff_diff - differences between GNU troff and classical troff

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 language as well as the intermediate
       output format (troff output).

       The section SEE ALSO 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 classical Unix 7 troff are described in
detail.

Long names
The names of number registers, fonts, strings/macros/diversions, special 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. Example: ‘\[A ho]’ is capital letter A
with ogonek which finally maps to glyph name ‘u0041_0328’. See the groff info file for details
how a glyph name for a composite glyph is constructed, and groff_char(7) for a list of glyph name
components used in composite 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 specified in the DESC file (1 by
default). There is a new scale indicator 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 argument 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 equivalent 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 expression whose default scale indicator
was neither u nor z, and so troff disallows this. Similarly it would make no sense to use a scaling
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 request. 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 recent versions of UNIX and is available in compatibility mode.

\E This is equivalent to an escape character, but it is not interpreted in copy mode. For example,
strings to start and end superscripting 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 sequence can be conveniently used in
conjunction with the char request, 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 device 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[opminy], \n[opmaxx], and \n[opmaxy]
to -1. These four registers 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, enable 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 boundary).

\O4 End a nesting level.

\O5[Pfilename]
This escape is grohtml specific. Provided that this escape 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 returned 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 extension 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 position; anything may not contain
tabs or leaders.

\$0 The name by which the current macro was invoked. The als request 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 diversion is reread, anything is interpreted. anything may not contain
newlines; use \! if you want to embed newlines in a diversion. The escape sequence \? is also
recognized in copy mode and 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 followed 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 undefined, 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 object named yy. The new name and the
old name are exactly equivalent (it is similar to a hard rather than a soft link). If yy is
undefined, a warning of type mac is generated, and the request 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 request; 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
‘compatibility restore’ token at the end. As a consequence, the requests 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 compatibility 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 conjunction 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 requests. 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 characters -\[hy]\[em] 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.

8 The glyph associated with this character overlaps horizontally (initially characters
\[ul]\[rn]\[ru]\[radicalex]\[sqrtex] have this property).

16 The glyph associated with this character overlaps vertically (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 characters. Use this in combination with
values 2 and 4 (initially 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 combination with flags 256 and 512 and has no effect otherwise.

256 Prohibit a line break after the character, but allow a line break before the character.
This works only in combination with flags 128 and 512 and has no effect otherwise.

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 neighbour 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 character is set
to \ while string is being processed. Any emboldening, 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 sequences; 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 acceptable 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 default), otherwise disable them.

.cp n If n is non-zero or missing, enable compatibility mode, otherwise disable it. In compatibility
mode, long names are not recognized, and the incompatibilities 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 components), and gray or grey (one component). Color components can be
given either as a hexadecimal string or as positive decimal integers in the range 0–65535. A
hexadecimal string contains all color components concatenated; it must start with either # 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
specify 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 redefined. 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 families.

.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 difference 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 previous 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
requests, 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 integer multiple of 1/1000th. If it is
missing or is equal to zero, it means the same as 1000, namely no magnification. f must be a real
font name, not a style.

.gcolor c
Set the glyph color to c. If c is missing, switch to the previous 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 hyphenation code which is the lower-case version of itself. See also
the hpf request.

.hla lang
Set the current hyphenation language to lang. Hyphenation exceptions specified with the hw
request and hyphenation patterns specified with the hpf request are both associated with the
current 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 associated 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 comment).

Use the hpfcode request to map the encoding used in hyphenation patterns files to groff's input
encoding. By default, everything 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 invoked by the troffrc file; a second call replaces the old patterns
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 language.

.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 recently read patterns to character code b, character code c to d,
etc. Initially, all character codes map to themselves. The arguments of hpfcode must be integers
in the range 0 to 255. Note that it is even possible to use character codes which are invalid 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 hyphenation 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 default
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 counts as one 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 register 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 distances are computed relative to the (current) output line. Otherwise
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 behaviour; the leading spaces are removed. Registers \n[lsn] and
\n[lss] hold the number of removed leading spaces and the corresponding 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 the -m command line option. 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 truncating 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 allow
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 bounding 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 output. 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
applied 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 a 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 hyphenated
at a line break. If the soft hyphen character does not exist 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 becomes argument i-n; arguments 1 to n
are no longer available. If n is missing, arguments are shifted by 1. Shifting by negative
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. Contrary 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 special 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 example,
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 family 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 index 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 written 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 subject 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 request uses the character code (if
any) before the character translation. Example:

.trin ax
.di xxx
a
.br
.di
.xxx
.trin aa
.asciify xxx
.xxx

The result is x a. Using tr, the result would be x x.

.trnt abcd
This is the same as the tr request except that the translations do not apply to text that is
transparently throughput into a diversion with \!. For example,

.tr ab
.di x
\!.tm a
.di
.x

prints b; if trnt is used instead of tr it prints a.

.troff Make the n built-in condition false, and the t built-in condition 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, .unformat
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 position
traps. The parameter that controls whether vertical position 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 disabled. 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 previously 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 accepted. See subsection Drawing Commands
below for more information.

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 behaviour 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’ token at
the end, with compatibility mode switched on during execution.

.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 environments. There
is no limit on the number of named environments; they are created the first time that they are
referenced.

.ss m n
When two arguments are given to the ss request, the second argument 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 are exactly that exhibited by GNU troff if a second argument is never given to the ss
request. 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 to reliably modify 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-valued 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 request, 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 request.

\n[.rj]
The number of lines to be right-justified as set by the rj request.

\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 a 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 actually 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 enabled 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 argument, 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 horizontal 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 register \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 to 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 \\$@

\\*[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 different input levels to the first
delimiter character are not recognized as the second or third delimiters. This applies also to the tl
request. In a \w escape sequence, a character that appears at a different 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 different input level to the starting delimiter character is not
recognized 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 delimiter 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 either an ASCII character or a glyph
(special character) \N'xxx', \(xx or \[xxx]; the condition is also true if ch has been defined 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 applied), without actually mounting it.

.if Ss True if style s has been registered. Font translation is applied.

The tr request can now map characters onto \~.

The space width emitted by the \| and \^ escape sequences can be controlled on a per-font basis. If
there is a glyph named \| or \^, respectively (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 format used by GNU troff is very
similar to that used by Unix device-independent 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 following 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 character
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 default 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 underlining 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
correspond 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 horizontal 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 vertical diameter of dy with the
leftmost point at the current position.

Dp dx1 dy1 dx2 dy2 ... dxn dyn\n
--

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 to process 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 considered 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 sequences in names.

Fractional point sizes cause one noteworthy incompatibility. In classical 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 immediately before the glyph is added
to the current output line. Macros, diversions and strings are all, in fact, the same type of object;
they contain lists of input characters and glyphs in any combination.

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 backslashes ‘\\’ 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 character is not redefined. It works in both GNU mode and compatibility
mode, while dirty tricks like specifying a sequence of multiple backslashes 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 facility 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 classical ‘device-independent’ troff
did.

COPYING

       Copyright © 1989-2014 Free Software Foundation, Inc.

       This file is part of groff, the GNU  roff  type-setting  system.   It  is  the  source  of  the  man-page
       groff_diff(7).

       Permission  is  granted  to  copy, distribute and/or modify this document under the terms of the GNU Free
       Documentation License, Version 1.3 or any later version published by the Free Software  Foundation;  with
       no Front-Cover Texts, and with no Back-Cover Texts.

       A  copy  of  the Free Documentation License is included as a file called FDL in the main directory of the
       groff source package, it is also available in  the  internet  at  GNU  FDL  license  ⟨http://www.gnu.org/
       copyleft/fdl.html⟩.

AUTHORS

       This  document  was  written by James Clark ⟨jjc@jclark.com⟩, was modified by Werner Lemberg ⟨wl@gnu.org⟩
       and Bernd Warken ⟨groff-bernd.warken-72@web.de⟩.