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
inludes 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 color (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, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010 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