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freebsd-dev/contrib/groff/doc/groff-4
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This is groff, produced by makeinfo version 4.2 from ./groff.texinfo.
This manual documents GNU `troff' version 1.18.
Copyright (C) 1994-2000, 2001, 2002 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.1 or any later version published by the Free Software
Foundation; with no Invariant Sections, with the Front-Cover texts
being `A GNU Manual," and with the Back-Cover Texts as in (a)
below. A copy of the license is included in the section entitled
`GNU Free Documentation License."
(a) The FSF's Back-Cover Text is: `You have freedom to copy and
modify this GNU Manual, like GNU software. Copies published by
the Free Software Foundation raise funds for GNU development."
INFO-DIR-SECTION Miscellaneous
START-INFO-DIR-ENTRY
* Groff: (groff). The GNU troff document formatting system.
END-INFO-DIR-ENTRY

File: groff, Node: Manipulating Hyphenation, Next: Manipulating Spacing, Prev: Manipulating Filling and Adjusting, Up: gtroff Reference
Manipulating Hyphenation
========================
As discussed in *Note Hyphenation::, `gtroff' hyphenates words.
There are a number of ways to influence hyphenation.
- Request: .hy [mode]
- Register: \n[.hy]
Enable hyphenation. The request has an optional numeric argument,
MODE, to restrict hyphenation if necessary:
`1'
The default argument if MODE is omitted. Hyphenate without
restrictions. This is also the start-up value of `gtroff'.
`2'
Do not hyphenate the last word on a page or column.
`4'
Do not hyphenate the last two characters of a word.
`8'
Do not hyphenate the first two characters of a word.
Values in the previous table are additive. For example, the
value 12 causes `gtroff' to neither hyphenate the last two nor the
first two characters of a word.
The current hyphenation restrictions can be found in the read-only
number register `.hy'.
The hyphenation mode is associated with the current environment
(*note Environments::).
- Request: .nh
Disable hyphenation (i.e., set the hyphenation mode to zero). Note
that the hyphenation mode of the last call to `hy' is not
remembered.
The hyphenation mode is associated with the current environment
(*note Environments::).
- Request: .hlm [nnn]
- Register: \n[.hlm]
- Register: \n[.hlc]
Set the maximum number of consecutive hyphenated lines to NNN. If
this number is negative, there is no maximum. The default value
is -1 if NNN is omitted. This value is associated with the
current environment (*note Environments::). Only lines output
from a given environment count towards the maximum associated with
that environment. Hyphens resulting from `\%' are counted;
explicit hyphens are not.
The current setting of `hlm' is available in the `.hlm' read-only
number register. Also the number of immediately preceding
consecutive hyphenated lines are available in the read-only number
register `.hlc'.
- Request: .hw word1 word2 ...
Define how WORD1, WORD2, etc. are to be hyphenated. The words
must be given with hyphens at the hyphenation points. For example:
.hw in-sa-lub-rious
Besides the space character, any character whose hyphenation code
value is zero can be used to separate the arguments of `hw' (see
the documentation for the `hcode' request below for more
information). In addition, this request can be used more than
once.
Hyphenation exceptions specified with the `hw' request are
associated with the current hyphenation language; it causes an
error if there is no current hyphenation language.
This request is ignored if there is no parameter.
In old versions of `troff' there was a limited amount of space to
store such information; fortunately, with `gtroff', this is no
longer a restriction.
- Escape: \%
- Escape: \:
To tell `gtroff' how to hyphenate words on the fly, use the `\%'
escape, also known as the "hyphenation character". Preceding a
word with this character prevents it from being hyphenated;
putting it inside a word indicates to `gtroff' that the word may
be hyphenated at that point. Note that this mechanism only
affects that one occurrence of the word; to change the hyphenation
of a word for the entire document, use the `hw' request.
The `\:' escape inserts a zero-width break point (that is, the
word breaks but without adding a hyphen).
... check the /var/log/\:httpd/\:access_log file ...
Note that `\X' and `\Y' start a word, that is, the `\%' escape in
(say) ` \X'...'\%foobar' and ` \Y'...'\%foobar' no longer prevents
hyphenation but inserts a hyphenation point at the beginning of
`foobar'; most likely this isn't what you want to do.
- Request: .hc [char]
Change the hyphenation character to CHAR. This character then
works the same as the `\%' escape, and thus, no longer appears in
the output. Without an argument, `hc' resets the hyphenation
character to be `\%' (the default) only.
The hyphenation character is associated with the current
environment (*note Environments::).
- Request: .hpf pattern_file
- Request: .hpfa pattern_file
- Request: .hpfcode a b [c d ...]
Read in a file of hyphenation patterns. This file is searched for
in the same way as `NAME.tmac' (or `tmac.NAME') is searched for if
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).
If no `hpf' request is specified (either in the document or in a
macro package), `gtroff' won't hyphenate at all.
The `hpfa' request appends a file of patterns to the current list.
The `hpfcode' request defines mapping values for character codes in
hyphenation patterns. `hpf' or `hpfa' then apply the mapping
(after reading the patterns) before replacing or appending them to
the current list of patterns. Its arguments are pairs of
character codes - integers from 0 to 255. The request maps
character code A to code B, code C to code D, and so on. You can
use character codes which would be invalid otherwise.
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' or `troffrc-end' file; by default,
`troffrc' loads hyphenation patterns for American English (in file
`hyphen.us').
A second call to `hpf' (for the same language) will replace the
hyphenation patterns with the new ones.
Invoking `hpf' causes an error if there is no current hyphenation
language.
- Request: .hcode c1 code1 c2 code2 ...
Set the hyphenation code of character C1 to CODE1, that of C2 to
CODE2, etc. 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 its hyphenation
code set to itself, and each upper-case letter (`A'-`Z') has a
hyphenation code which is the lower-case version of itself.
This request is ignored if it has no parameter.
- Request: .hym [length]
- Register: \n[.hym]
Set the (right) hyphenation margin to LENGTH. If the current
adjustment mode is not `b' or `n', the line is not hyphenated if
it is shorter than LENGTH. Without an argument, the hyphenation
margin is reset to its default value, which is 0. The default
scaling indicator for this request is `m'. The hyphenation margin
is associated with the current environment (*note Environments::).
A negative argument resets the hyphenation margin to zero, emitting
a warning of type `range'.
The current hyphenation margin is available in the `.hym' read-only
number register.
- Request: .hys [hyphenation_space]
- Register: \n[.hys]
Set the hyphenation space to HYPHENATION_SPACE. If the current
adjustment mode is `b' or `n', don't hyphenate the line if it can
be justified by adding no more than HYPHENATION_SPACE extra space
to each word space. Without argument, the hyphenation space is
set to its default value, which is 0. The default scaling
indicator for this request is `m'. The hyphenation space is
associated with the current environment (*note Environments::).
A negative argument resets the hyphenation space to zero, emitting
a warning of type `range'.
The current hyphenation space is available in the `.hys' read-only
number register.
- Request: .shc [glyph]
Set the "soft hyphen character" to GLYPH.(1) (*note Manipulating
Hyphenation-Footnote-1::) If the argument is omitted, the soft
hyphen character is set to the default glyph `\(hy' (this is the
start-up value of `gtroff' also). The soft hyphen character is
the glyph that is inserted when a word is hyphenated at a line
break. If the soft hyphen character does not exist in the font of
the character 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.
- Request: .hla language
- Register: \n[.hla]
Set the current hyphenation language to the string LANGUAGE.
Hyphenation exceptions specified with the `hw' request and
hyphenation patterns specified with the `hpf' and `hpfa' requests
are both associated with the current hyphenation language. The
`hla' request is usually invoked by the `troffrc' or the
`troffrc-end' files; `troffrc' sets the default language to `us'.
The current hyphenation language is available as a string in the
read-only number register `.hla'.
.ds curr_language \n[.hla]
\*[curr_language]
=> us

File: groff, Node: Manipulating Hyphenation-Footnotes, Up: Manipulating Hyphenation
(1) "Soft hyphen character" is a misnomer since it is an output
glyph.

File: groff, Node: Manipulating Spacing, Next: Tabs and Fields, Prev: Manipulating Hyphenation, Up: gtroff Reference
Manipulating Spacing
====================
- Request: .sp [distance]
Space downwards DISTANCE. With no argument it advances 1 line. A
negative argument causes `gtroff' to move up the page the
specified distance. If the argument is preceded by a `|' then
`gtroff' moves that distance from the top of the page. This
request causes a line break. The default scaling indicator is `v'.
- Request: .ls [nnn]
- Register: \n[.L]
Output NNN-1 blank lines after each line of text. With no
argument, `gtroff' uses the previous value before the last `ls'
call.
.ls 2 \" This causes double-spaced output
.ls 3 \" This causes triple-spaced output
.ls \" Again double-spaced
The line spacing is associated with the current environment (*note
Environments::).
The read-only number register `.L' contains the current line
spacing setting.
*Note Changing Type Sizes::, for the requests `vs' and `pvs' as
alternatives to `ls'.
- Escape: \x'SPACING'
- Register: \n[.a]
Sometimes, extra vertical spacing is only needed occasionally, e.g.
to allow space for a tall construct (like an equation). The `\x'
escape does this. The escape is given a numerical argument,
usually enclosed in quotes (like `\x'3p''); the default scaling
indicator is `v'. If this number is positive extra vertical space
is inserted below the current line. A negative number adds space
above. If this escape is used multiple times on the same line,
the maximum of the values is used.
*Note Escapes::, for details on parameter delimiting characters.
The `.a' read-only number register contains the most recent
(nonnegative) extra vertical line space.
Using `\x' can be necessary in combination with the `\b' escape,
as the following example shows.
This is a test with the \[rs]b escape.
.br
This is a test with the \[rs]b escape.
.br
This is a test with \b'xyz'\x'-1m'\x'1m'.
.br
This is a test with the \[rs]b escape.
.br
This is a test with the \[rs]b escape.
produces
This is a test with the \b escape.
This is a test with the \b escape.
x
This is a test with y.
z
This is a test with the \b escape.
This is a test with the \b escape.
- Request: .ns
- Request: .rs
- Register: \n[.ns]
Enable "no-space mode". In this mode, spacing (either via `sp' or
via blank lines) is disabled. The `bp' request to advance to the
next page is also disabled, except if it is accompanied by a page
number (see *Note Page Control::, for more information). This
mode ends when actual text is output or the `rs' request is
encountered which ends no-space mode. The read-only number
register `.ns' is set to 1 as long as no-space mode is active.
This request is useful for macros that conditionally insert
vertical space before the text starts (for example, a paragraph
macro could insert some space except when it is the first
paragraph after a section header).

File: groff, Node: Tabs and Fields, Next: Character Translations, Prev: Manipulating Spacing, Up: gtroff Reference
Tabs and Fields
===============
A tab character (ASCII char 9, EBCDIC char 5) causes a horizontal
movement to the next tab stop (much like it did on a typewriter).
- Escape: \t
This escape is a non-interpreted tab character. In copy mode
(*note Copy-in Mode::), `\t' is the same as a real tab character.
- Request: .ta [n1 n2 ... nn T r1 r2 ... rn]
- Register: \n[.tabs]
Change tab stop positions. This request takes a series of tab
specifiers as arguments (optionally divided into two groups with
the letter `T') which indicate where each tab stop is to be
(overriding any previous settings).
Tab stops can be specified absolutely, i.e., as the distance from
the left margin. For example, the following sets 6 tab stops every
one inch.
.ta 1i 2i 3i 4i 5i 6i
Tab stops can also be specified using a leading `+' which means
that the specified tab stop is set relative to the previous tab
stop. For example, the following is equivalent to the previous
example.
.ta 1i +1i +1i +1i +1i +1i
`gtroff' supports an extended syntax to specify repeat values after
the `T' mark (these values are always taken as relative) - this is
the usual way to specify tabs set at equal intervals. The
following is, yet again, the same as the previous examples. It
does even more since it defines an infinite number of tab stops
separated by one inch.
.ta T 1i
Now we are ready to interpret the full syntax given at the
beginning: 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.
Example: `4c +6c T 3c 5c 2c' is equivalent to `4c 10c 13c 18c 20c
23c 28c 30c ...'.
The material in each tab column (i.e., the column between two tab
stops) may be justified to the right or left or centered in the
column. This is specified by appending `R', `L', or `C' to the tab
specifier. The default justification is `L'. Example:
.ta 1i 2iC 3iR
Some notes:
* The default unit of the `ta' request is `m'.
* A tab stop is converted into a non-breakable horizontal
movement which can be neither stretched nor squeezed. For
example,
.ds foo a\tb\tc
.ta T 5i
\*[foo]
creates a single line which is a bit longer than 10 inches (a
string is used to show exactly where the tab characters are).
Now consider the following:
.ds bar a\tb b\tc
.ta T 5i
\*[bar]
`gtroff' first converts the tab stops of the line into
unbreakable horizontal movements, then splits the line after
the second `b' (assuming a sufficiently short line length).
Usually, this isn't what the user wants.
* Superfluous tabs (i.e., tab characters which do not
correspond to a tab stop) are ignored except the first one
which delimits the characters belonging to the last tab stop
for right-justifying or centering. Consider the following
example
.ds Z foo\tbar\tfoo
.ds ZZ foo\tbar\tfoobar
.ds ZZZ foo\tbar\tfoo\tbar
.ta 2i 4iR
\*[Z]
.br
\*[ZZ]
.br
\*[ZZZ]
.br
which produces the following output:
foo bar foo
foo bar foobar
foo bar foobar
The first line right-justifies the second `foo' relative to
the tab stop. The second line right-justifies `foobar'. The
third line finally right-justifies only `foo' because of the
additional tab character which marks the end of the string
belonging to the last defined tab stop.
* Tab stops are associated with the current environment (*note
Environments::).
* Calling `ta' without an argument removes all tab stops.
* The start-up value of `gtroff' is `T 0.5i' in troff mode and
`T 0.8i' in nroff mode (the latter is done with an explicit
call to the `ta' request in the file `tty.tmac'.
The read-only number register `.tabs' contains a string
representation of the current tab settings suitable for use as an
argument to the `ta' request.
.ds tab-string \n[.tabs]
\*[tab-string]
=> T120u
The `troff' version of the Plan 9 operating system uses register
`.S' for the same purpose.
- Request: .tc [fill-glyph]
Normally `gtroff' fills the space to the next tab stop with
whitespace. This can be changed with the `tc' request. With no
argument `gtroff' reverts to using whitespace, which is the
default. The value of this "tab repetition character" is
associated with the current environment (*note Environments::).(1)
(*note Tabs and Fields-Footnote-1::)
- Request: .linetabs n
- Register: \n[.linetabs]
If N is missing or not zero, enable "line-tabs" mode, or disable
it otherwise (the default). In line-tabs mode, `gtroff' computes
tab distances relative to the (current) output line instead of the
input line.
For example, the following code:
.ds x a\t\c
.ds y b\t\c
.ds z c
.ta 1i 3i
\*x
\*y
\*z
in normal mode, results in the output
a b c
in line-tabs mode, the same code outputs
a b c
Line-tabs mode is associated with the current environment. The
read-only register `.linetabs' is set to 1 if in line-tabs mode,
and 0 in normal mode.
* Menu:
* Leaders::
* Fields::

File: groff, Node: Tabs and Fields-Footnotes, Up: Tabs and Fields
(1) "Tab repetition character" is a misnomer since it is an output
glyph.

File: groff, Node: Leaders, Next: Fields, Prev: Tabs and Fields, Up: Tabs and Fields
Leaders
-------
Sometimes it may may be desirable to use the `tc' request to fill a
particular tab stop with a given glyph (for example dots in a table of
contents), but also normal tab stops on the rest of the line. For this
`gtroff' provides an alternate tab mechanism, called "leaders" which
does just that.
A leader character (character code 1) behaves similarly to a tab
character: It moves to the next tab stop. The only difference is that
for this movement, the fill glyph defaults to a period character and
not to space.
- Escape: \a
This escape is a non-interpreted leader character. In copy mode
(*note Copy-in Mode::), `\a' is the same as a real leader
character.
- Request: .lc [fill-glyph]
Declare the "leader repetition character".(1) (*note
Leaders-Footnote-1::) Without an argument, leaders act the same as
tabs (i.e., using whitespace for filling). `gtroff''s start-up
value is a dot (`.'). The value of the leader repetition
character is associated with the current environment (*note
Environments::).
For a table of contents, to name an example, tab stops may be
defined so that the section number is one tab stop, the title is the
second with the remaining space being filled with a line of dots, and
then the page number slightly separated from the dots.
.ds entry 1.1\tFoo\a\t12
.lc .
.ta 1i 5i +.25i
\*[entry]
This produces
1.1 Foo.......................................... 12

File: groff, Node: Leaders-Footnotes, Up: Leaders
(1) "Leader repetition character" is a misnomer since it is an
output glyph.

File: groff, Node: Fields, Prev: Leaders, Up: Tabs and Fields
Fields
------
"Fields" are a more general way of laying out tabular data. A field
is defined as the data between a pair of "delimiting characters". It
contains substrings which are separated by "padding characters". The
width of a field is the distance on the _input_ line from the position
where the field starts to the next tab stop. A padding character
inserts stretchable space similar to TeX's `\hss' command (thus it can
even be negative) to make the sum of all substring lengths plus the
stretchable space equal to the field width. If more than one padding
character is inserted, the available space is evenly distributed among
them.
- Request: .fc [delim-char [padding-char]]
Define a delimiting and a padding character for fields. If the
latter is missing, the padding character defaults to a space
character. If there is no argument at all, the field mechanism is
disabled (which is the default). Note that contrary to e.g. the
tab repetition character, delimiting and padding characters are
_not_ associated to the current environment (*note Environments::).
Example:
.fc # ^
.ta T 3i
#foo^bar^smurf#
.br
#foo^^bar^smurf#
and here the result:
foo bar smurf
foo bar smurf

File: groff, Node: Character Translations, Next: Troff and Nroff Mode, Prev: Tabs and Fields, Up: gtroff Reference
Character Translations
======================
The control character (`.') and the no-break control character (`'')
can be changed with the `cc' and `c2' requests, respectively.
- Request: .cc [c]
Set the control character to C. With no argument the default
control character `.' is restored. The value of the control
character is associated with the current environment (*note
Environments::).
- Request: .c2 [c]
Set the no-break control character to C. With no argument the
default control character `'' is restored. The value of the
no-break control character is associated with the current
environment (*note Environments::).
- Request: .eo
Disable the escape mechanism completely. After executing this
request, the backslash character `\' no longer starts an escape
sequence.
This request can be very helpful in writing macros since it is not
necessary then to double the escape character. Here an example:
.\" This is a simplified version of the
.\" .BR request from the man macro package
.eo
.de BR
. ds result \&
. while (\n[.$] >= 2) \{\
. as result \fB\$1\fR\$2
. shift 2
. \}
. if \n[.$] .as result \fB\$1
\*[result]
. ft R
..
.ec
- Request: .ec [c]
Set the escape character to C. With no argument the default
escape character `\' is restored. It can be also used to
re-enable the escape mechanism after an `eo' request.
Note that changing the escape character globally will likely break
macro packages since `gtroff' has no mechanism to `intern' macros,
i.e., to convert a macro definition into an internal form which is
independent of its representation (TeX has this mechanism). If a
macro is called, it is executed literally.
- Request: .ecs
- Request: .ecr
The `ecs' request saves the current escape character in an
internal register. Use this request in combination with the `ec'
request to temporarily change the escape character.
The `ecr' request restores the escape character saved with `ecs'.
Without a previous call to `ecs', this request sets the escape
character to `\'.
- Escape: \\
- Escape: \e
- Escape: \E
Print the current escape character (which is the backslash
character `\' by default).
`\\' is a `delayed' backslash; more precisely, it is the default
escape character followed by a backslash, which no longer has
special meaning due to the leading escape character. It is _not_
an escape sequence in the usual sense! In any unknown escape
sequence `\X' the escape character is ignored and X is printed.
But if X is equal to the current escape character, no warning is
emitted.
As a consequence, only at top-level or in a diversion a backslash
glyph is printed; in copy-in mode, it expands to a single
backslash which then combines with the following character to an
escape sequence.
The `\E' escape differs from `\e' by printing an escape character
that is not interpreted in copy mode. Use this to define strings
with escapes that work when used in copy mode (for example, as a
macro argument). The following example defines strings to begin
and end a superscript:
.ds { \v'-.3m'\s'\Es[.s]*60/100'
.ds } \s0\v'.3m'
Another example to demonstrate the differences between the various
escape sequences, using a strange escape character, `-'.
.ec -
.de xxx
--A'123'
..
.xxx
=> -A'foo'
The result is surprising for most users, expecting `1' since `foo'
is a valid identifier. What has happened? As mentioned above,
the leading escape character makes the following character
ordinary. Written with the default escape character the sequence
`--' becomes `\-' - this is the minus sign.
If the escape character followed by itself is a valid escape
sequence, only `\E' yields the expected result:
.ec -
.de xxx
-EA'123'
..
.xxx
=> 1
- Escape: \.
Similar to `\\', the sequence `\.' isn't a real escape sequence.
As before, a warning message is suppressed if the escape character
is followed by a dot, and the dot itself is printed.
.de foo
. nop foo
.
. de bar
. nop bar
\\..
.
..
.foo
.bar
=> foo bar
The first backslash is consumed while the macro is read, and the
second is swallowed while exexuting macro `foo'.
A "translation" is a mapping of an input character to an output
glyph. The mapping occurs at output time, i.e., the input character
gets assigned the metric information of the mapped output character
right before input tokens are converted to nodes (*note Gtroff
Internals::, for more on this process).
- Request: .tr abcd...
- Request: .trin abcd...
Translate character A to glyph B, character C to glyph D, etc. If
there is an odd number of arguments, the last one is translated to
an unstretchable space (`\ ').
The `trin' request is identical to `tr', but when you unformat a
diversion with `asciify' it ignores the translation. *Note
Diversions::, for details about the `asciify' request.
Some notes:
* Special characters (`\(XX', `\[XXX]', `\C'XXX'', `\'', `\`',
`\-', `\_'), glyphs defined with the `char' request, and
numbered glyphs (`\N'XXX'') can be translated also.
* The `\e' escape can be translated also.
* Characters can be mapped onto the `\%' and `\~' escapes (but
`\%' and `\~' can't be mapped onto another glyph).
* The following characters can't be translated: space (with one
exception, see below), backspace, newline, leader (and `\a'),
tab (and `\t').
* Translations are not considered for finding the soft hyphen
character set with the `shc' request.
* The pair `C\&' (this is an arbitrary character C followed by
the zero width space character) maps this character to
nothing.
.tr a\&
foo bar
=> foo br
It is even possible to map the space character to nothing:
.tr aa \&
foo bar
=> foobar
As shown in the example, the space character can't be the
first character/glyph pair as an argument of `tr'.
Additionally, it is not possible to map the space character
to any other glyph; requests like `.tr aa x' undo `.tr aa \&'
instead.
If justification is active, lines are justified in spite of
the `empty' space character (but there is no minimal
distance, i.e. the space character, between words).
* After an output glyph has been constructed (this happens at
the moment immediately before the glyph is appended to an
output glyph list, either by direct output, in a macro,
diversion, or string), it is no longer affected by `tr'.
* Translating character to glyphs where one of them or both are
undefined is possible also; `tr' does not check whether the
entities in its argument do exist.
*Note Gtroff Internals::.
* `troff' no longer has a hard-coded dependency on Latin-1; all
`charXXX' entities have been removed from the font
description files. This has a notable consequence which
shows up in warnings like `can't find character with input
code XXX' if the `tr' request isn't handled properly.
Consider the following translation:
.tr e'E'
This maps input character `e'' onto glyph `E'', which is
identical to glyph `char201'. But this glyph intentionally
doesn't exist! Instead, `\[char201]' is treated as an input
character entity and is by default mapped onto `\['E]', and
`gtroff' doesn't handle translations of translations.
The right way to write the above translation is
.tr e'\['E]
With other words, the first argument of `tr' should be an
input character or entity, and the second one a glyph entity.
* Without an argument, the `tr' request is ignored.
- Request: .trnt abcd...
`trnt' is the same as the `tr' request except that the
translations do not apply to text that is transparently throughput
into a diversion with `\!'. *Note Diversions::, for more
information.
For example,
.tr ab
.di x
\!.tm a
.di
.x
prints `b' to the standard error stream; if `trnt' is used instead
of `tr' it prints `a'.

File: groff, Node: Troff and Nroff Mode, Next: Line Layout, Prev: Character Translations, Up: gtroff Reference
Troff and Nroff Mode
====================
Originally, `nroff' and `troff' were two separate programs, the
former for TTY output, the latter for everything else. With GNU
`troff', both programs are merged into one executable, sending its
output to a device driver (`grotty' for TTY devices, `grops' for
POSTSCRIPT, etc.) which interprets the intermediate output of `gtroff'.
For UNIX `troff' it makes sense to talk about "Nroff mode" and "Troff
mode" since the differences are hardcoded. For GNU `troff', this
distinction is not appropriate because `gtroff' simply takes the
information given in the font files for a particular device without
handling requests specially if a TTY output device is used.
Usually, a macro package can be used with all output devices.
Nevertheless, it is sometimes necessary to make a distinction between
TTY and non-TTY devices: `gtroff' provides two built-in conditions `n'
and `t' for the `if', `ie', and `while' requests to decide whether
`gtroff' shall behave like `nroff' or like `troff'.
- Request: .troff
Make the `t' built-in condition true (and the `n' built-in
condition false) for `if', `ie', and `while' conditional requests.
This is the default if `gtroff' (_not_ `groff') is started with
the `-R' switch to avoid loading of the start-up files `troffrc'
and `troffrc-end'. Without `-R', `gtroff' stays in troff mode if
the output device is not a TTY (e.g. `ps').
- Request: .nroff
Make the `n' built-in condition true (and the `t' built-in
condition false) for `if', `ie', and `while' conditional requests.
This is the default if `gtroff' uses a TTY output device; the
code for switching to nroff mode is in the file `tty.tmac' which
is loaded by the start-up file `troffrc'.
*Note Conditionals and Loops::, for more details on built-in
conditions.

File: groff, Node: Line Layout, Next: Line Control, Prev: Troff and Nroff Mode, Up: gtroff Reference
Line Layout
===========
The following drawing shows the dimensions which `gtroff' uses for
placing a line of output onto the page. They are labeled with the
request which manipulates each dimension.
-->| in |<--
|<-----------ll------------>|
+----+----+----------------------+----+
| : : : |
+----+----+----------------------+----+
-->| po |<--
|<--------paper width---------------->|
These dimensions are:
`po'
"Page offset" - this is the leftmost position of text on the final
output, defining the "left margin".
`in'
"Indentation" - this is the distance from the left margin where
text is printed.
`ll'
"Line length" - this is the distance from the left margin to right
margin.
A simple demonstration:
.ll 3i
This is text without indentation.
The line length has been set to 3\~inch.
.in +.5i
.ll -.5i
Now the left and right margins are both increased.
.in
.ll
Calling .in and .ll without parameters restore
the previous values.
Result:
This is text without indenta-
tion. The line length has
been set to 3 inch.
Now the left and
right margins are
both increased.
Calling .in and .ll without
parameters restore the previ-
ous values.
- Request: .po [offset]
- Request: .po +offset
- Request: .po -offset
- Register: \n[.o]
Set horizontal page offset to OFFSET (or increment or decrement
the current value by OFFSET). Note that this request does not
cause a break, so changing the page offset in the middle of text
being filled may not yield the expected result. The initial value
is 1i. For TTY output devices, it is set to 0 in the startup file
`troffrc'; the default scaling indicator is `m' (and not `v' as
incorrectly documented in the original UNIX troff manual).
The current page offset can be found in the read-only number
register `.o'.
If `po' is called without an argument, the page offset is reset to
the previous value before the last call to `po'.
.po 3i
\n[.o]
=> 720
.po -1i
\n[.o]
=> 480
.po
\n[.o]
=> 720
- Request: .in [indent]
- Request: .in +indent
- Request: .in -indent
- Register: \n[.i]
Set indentation to INDENT (or increment or decrement the current
value by INDENT). This request causes a break. Initially, there
is no indentation.
If `in' is called without an argument, the indentation is reset to
the previous value before the last call to `in'. The default
scaling indicator is `m'.
The indentation is associated with the current environment (*note
Environments::).
If a negative indentation value is specified (which is not
allowed), `gtroff' emits a warning of type `range' and sets the
indentation to zero.
The effect of `in' is delayed until a partially collected line (if
it exists) is output. A temporary indent value is reset to zero
also.
The current indentation (as set by `in') can be found in the
read-only number register `.i'.
- Request: .ti offset
- Request: .ti +offset
- Request: .ti -offset
- Register: \n[.in]
Temporarily indent the next output line by OFFSET. If an
increment or decrement value is specified, adjust the temporary
indentation relative to the value set by the `in' request.
This request causes a break; its value is associated with the
current environment (*note Environments::). The default scaling
indicator is `m'. A call of `ti' without an argument is ignored.
If the total indentation value is negative (which is not allowed),
`gtroff' emits a warning of type `range' and sets the temporary
indentation to zero. `Total indentation' is either OFFSET if
specified as an absolute value, or the temporary plus normal
indentation, if OFFSET is given as a relative value.
The effect of `ti' is delayed until a partially collected line (if
it exists) is output.
The read-only number register `.in' is the indentation that applies
to the current output line.
The difference between `.i' and `.in' is that the latter takes
into account whether a partially collected line still uses the old
indentation value or a temporary indentation value is active.
- Request: .ll [length]
- Request: .ll +length
- Request: .ll -length
- Register: \n[.l]
- Register: \n[.ll]
Set the line length to LENGTH (or increment or decrement the
current value by LENGTH). Initially, the line length is set to
6.5i. The effect of `ll' is delayed until a partially collected
line (if it exists) is output. The default scaling indicator is
`m'.
If `ll' is called without an argument, the line length is reset to
the previous value before the last call to `ll'. If a negative
line length is specified (which is not allowed), `gtroff' emits a
warning of type `range' and sets the line length to zero.
The line length is associated with the current environment (*note
Environments::).
The current line length (as set by `ll') can be found in the
read-only number register `.l'. The read-only number register
`.ll' is the line length that applies to the current output line.
Similar to `.i' and `.in', the difference between `.l' and `.ll'
is that the latter takes into account whether a partially
collected line still uses the old line length value.

File: groff, Node: Line Control, Next: Page Layout, Prev: Line Layout, Up: gtroff Reference
Line Control
============
It is important to understand how `gtroff' handles input and output
lines.
Many escapes use positioning relative to the input line. For
example, this
This is a \h'|1.2i'test.
This is a
\h'|1.2i'test.
produces
This is a test.
This is a test.
The main usage of this feature is to define macros which act exactly
at the place where called.
.\" A simple macro to underline a word
.de underline
. nop \\$1\l'|0\[ul]'
..
In the above example, `|0' specifies a negative distance from the
current position (at the end of the just emitted argument `\$1') back
to the beginning of the input line. Thus, the `\l' escape draws a line
from right to left.
`gtroff' makes a difference between input and output line
continuation; the latter is also called "interrupting" a line.
- Escape: \<RET>
- Escape: \c
- Register: \n[.int]
Continue a line. `\<RET>' (this is a backslash at the end of a
line immediately followed by a newline) works on the input level,
suppressing the effects of the following newline in the input.
This is a \
.test
=> This is a .test
The `|' operator is also affected.
`\c' works on the output level. Anything after this escape on the
same line is ignored, except `\R' which works as usual. Anything
before `\c' on the same line will be appended to the current
partial output line. The next non-command line after an
interrupted line counts as a new input line.
The visual results depend on whether no-fill mode is active.
* If no-fill mode is active (using the `nf' request), the next
input text line after `\c' will be handled as a continuation
of the same input text line.
.nf
This is a \c
test.
=> This is a test.
* If fill mode is active (using the `fi' request), a word
interrupted with `\c' will be continued with the text on the
next input text line, without an intervening space.
This is a te\c
st.
=> This is a test.
Note that an intervening control line which causes a break is
stronger than `\c', flushing out the current partial line in the
usual way.
The `.int' register contains a positive value if the last output
line was interrupted with `\c'; this is associated with the
current environment (*note Environments::).

File: groff, Node: Page Layout, Next: Page Control, Prev: Line Control, Up: gtroff Reference
Page Layout
===========
`gtroff' provides some very primitive operations for controlling
page layout.
- Request: .pl [length]
- Request: .pl +length
- Request: .pl -length
- Register: \n[.p]
Set the "page length" to LENGTH (or increment or decrement the
current value by LENGTH). This is the length of the physical
output page. The default scaling indicator is `v'.
The current setting can be found in the read-only number register
`.p'.
Note that this only specifies the size of the page, not the top and
bottom margins. Those are not set by `gtroff' directly. *Note
Traps::, for further information on how to do this.
Negative `pl' values are possible also, but not very useful: No
trap is sprung, and each line is output on a single page (thus
suppressing all vertical spacing).
If no argument or an invalid argument is given, `pl' sets the page
length to 11i.
`gtroff' provides several operations which help in setting up top
and bottom titles (or headers and footers).
- Request: .tl 'left'center'right'
Print a "title line". It consists of three parts: a left
justified portion, a centered portion, and a right justified
portion. The argument separator `'' can be replaced with any
character not occurring in the title line. The `%' character is
replaced with the current page number. This character can be
changed with the `pc' request (see below).
Without argument, `tl' is ignored.
Some notes:
* A title line is not restricted to the top or bottom of a page.
* `tl' prints the title line immediately, ignoring a partially
filled line (which stays untouched).
* It is not an error to omit closing delimiters. For example,
`.tl /foo' is equivalent to `.tl /foo///': It prints a title
line with the left justified word `foo'; the centered and
right justfied parts are empty.
* `tl' accepts the same parameter delimiting characters as the
`\A' escape; see *Note Escapes::.
- Request: .lt [length]
- Request: .lt +length
- Request: .lt -length
- Register: \n[.lt]
The title line is printed using its own line length, which is
specified (or incremented or decremented) with the `lt' request.
Initially, the title line length is set to 6.5i. If a negative
line length is specified (which is not allowed), `gtroff' emits a
warning of type `range' and sets the title line length to zero.
The default scaling indicator is `m'. If `lt' is called without
an argument, the title length is reset to the previous value
before the last call to `lt'.
The current setting of this is available in the `.lt' read-only
number register; it is associated with the current environment
(*note Environments::).
- Request: .pn page
- Request: .pn +page
- Request: .pn -page
- Register: \n[.pn]
Change (increase or decrease) the page number of the _next_ page.
The only argument is the page number; the request is ignored
without a parameter.
The read-only number register `.pn' contains the number of the next
page: either the value set by a `pn' request, or the number of the
current page plus 1.
- Register: \n[%]
A read-write register holding the current page number.
- Request: .pc [char]
Change the page number character (used by the `tl' request) to a
different character. With no argument, this mechanism is disabled.
Note that this doesn't affect the number register `%'.
*Note Traps::.
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