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
- \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] 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
- .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
- In line-tabs mode, the same code gives
- 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
- 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 \\$@
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 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'.
. .
.\}
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
-
\n Draw a polygon with, for
, the i-th vertex at the current position
. At the moment, GNU pic only uses this command to generate triangles and
rectangles.
- DP
-
\n Like Dp but draw a solid rather than outlined polygon.
- Dt n\n
- Set the current line thickness to n machine units.
Traditionally 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
'
where
c is not one of
c,
e,
l,
a,
or
~, Unix troff treats each of the
as a horizontal quantity, and each of the
as a vertical quantity and assumes that the width of the drawn object is
, and that the height is
. (The assumption about the height can be seen by examining the
st and
sb registers after using such a
D command in a
\w
escape sequence). This rule also holds for all the original drawing commands
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
\n
the current position should be increased by
.
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 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
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.
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.
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.
AUTHORS¶
Copyright (C) 1989, 2001-2004, 2006-2010, 2012 Free Software Foundation, Inc.
This document is distributed under the terms of the FDL (GNU Free Documentation
License) version 1.3 or later. You should have received a copy of the FDL on
your system, it is also available on-line at the
GNU
copyleft site This document was written by James Clark, with modifications
by
Werner Lemberg and
Bernd
Warken
This document is part of
groff, the GNU roff distribution. Formerly, the
contents of this document was kept in the manual page
troff(1). Only
the parts dealing with the language aspects of the different
roff
systems were carried over into this document. The
troff command line
options and warnings are still documented in
troff(1).
SEE ALSO¶
The
groff info file, cf.
info(1) presents all groff
documentation within a single document.
- groff(1)
- A list of all documentation around groff.
- groff(7)
- A description of the groff language, including a short, but
complete reference of all predefined requests, registers, and escapes of
plain groff. From the command line, this is called using
- roff(7)
- A survey of roff systems, including pointers to further historical
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