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freebsd-dev/contrib/groff/doc/groff-6
Ruslan Ermilov bdbe8a18ed Virgin import of FSF groff v1.19
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This is groff, produced by makeinfo version 4.3d from ./groff.texinfo.
This manual documents GNU `troff' version 1.19.
Copyright (C) 1994-2000, 2001, 2002, 2003 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 Typesetting
START-INFO-DIR-ENTRY
* Groff: (groff). The GNU troff document formatting system.
END-INFO-DIR-ENTRY

File: groff, Node: Changing Type Sizes, Next: Fractional Type Sizes, Prev: Sizes, Up: Sizes
Changing Type Sizes
-------------------
- Request: .ps [size]
- Request: .ps +size
- Request: .ps -size
- Escape: \ssize
- Register: \n[.s]
Use the `ps' request or the `\s' escape to change (increase,
decrease) the type size (in points). Specify SIZE as either an
absolute point size, or as a relative change from the current size.
The size 0, or no argument, goes back to the previous size.
Default scaling indicator of `size' is `z'. If `size' is zero or
negative, it is set to 1u.
The read-only number register `.s' returns the point size in
points as a decimal fraction. This is a string. To get the point
size in scaled points, use the `.ps' register instead.
`.s' is associated with the current environment (*note
Environments::).
snap, snap,
.ps +2
grin, grin,
.ps +2
wink, wink, \s+2nudge, nudge,\s+8 say no more!
.ps 10
The `\s' escape may be called in a variety of ways. Much like
other escapes there must be a way to determine where the argument
ends and the text begins. Any of the following forms are valid:
`\sN'
Set the point size to N points. N must be either 0 or in the
range 4 to 39.
`\s+N'
`\s-N'
Increase or decrease the point size by N points. N must be
exactly one digit.
`\s(NN'
Set the point size to NN points. NN must be exactly two
digits.
`\s+(NN'
`\s-(NN'
`\s(+NN'
`\s(-NN'
Increase or decrease the point size by NN points. NN must be
exactly two digits.
Note that `\s' doesn't produce an input token in `gtroff'. As a
consequence, it can be used in requests like `mc' (which expects a
single character as an argument) to change the font on the fly:
.mc \s[20]x\s[0]
*Note Fractional Type Sizes::, for yet another syntactical form of
using the `\s' escape.
- Request: .sizes s1 s2 ... sn [0]
Some devices may only have certain permissible sizes, in which case
`gtroff' rounds to the nearest permissible size. The `DESC' file
specifies which sizes are permissible for the device.
Use the `sizes' request to change the permissible sizes for the
current output device. Arguments are in scaled points; the
`sizescale' line in the `DESC' file for the output device provides
the scaling factor. For example, if the scaling factor is 1000,
then the value 12000 is 12 points.
Each argument can be a single point size (such as `12000'), or a
range of sizes (such as `4000-72000'). You can optionally end the
list with a zero.
- Request: .vs [space]
- Request: .vs +space
- Request: .vs -space
- Register: \n[.v]
Change (increase, decrease) the vertical spacing by SPACE. The
default scaling indicator is `p'.
If `vs' is called without an argument, the vertical spacing is
reset to the previous value before the last call to `vs'.
`gtroff' creates a warning of type `range' if SPACE is negative;
the vertical spacing is then set to the vertical resolution (as
given in the `.V' register).
The read-only number register `.v' contains the current vertical
spacing; it is associated with the current environment (*note
Environments::).
The effective vertical line spacing consists of four components.
* The vertical line spacing as set with the `vs' request.
* The "post-vertical line spacing" as set with the `pvs' request.
This is vertical space which will be added after a line has been
output.
* The "extra pre-vertical line space" as set with the `\x' request,
using a negative value. This is vertical space which will be
added once before the current line has been output.
* The "extra post-vertical line space" as set with the `\x' request,
using a positive value. This is vertical space which will be
added once after the current line has been output.
It is usually better to use `vs' or `pvs' instead of `ls' to produce
double-spaced documents: `vs' and `pvs' have a finer granularity for
the inserted vertical space compared to `ls'; furthermore, certain
preprocessors assume single-spacing.
*Note Manipulating Spacing::, for more details on the `\x' escape
and the `ls' request.
- Request: .pvs [space]
- Request: .pvs +space
- Request: .pvs -space
- Register: \n[.pvs]
Change (increase, decrease) the post-vertical spacing by SPACE.
The default scaling indicator is `p'.
If `pvs' is called without an argument, the post-vertical spacing
is reset to the previous value before the last call to `pvs'.
`gtroff' creates a warning of type `range' if SPACE is zero or
negative; the vertical spacing is then set to zero.
The read-only number register `.pvs' contains the current
post-vertical spacing; it is associated with the current
environment (*note Environments::).

File: groff, Node: Fractional Type Sizes, Prev: Changing Type Sizes, Up: Sizes
Fractional Type 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' which has the effect of multiplying by SIZESCALE.
Requests and escape sequences in `gtroff' 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 (see below).
For example, suppose SIZESCALE is 1000; then a scaled point is
equivalent to a millipoint; the request `.ps 10.25' is equivalent to
`.ps 10.25z' and thus sets the point size to 10250 scaled points, which
is equal to 10.25 points.
`gtroff' disallows the use of the `z' scale indicator in instances
where it would make no sense, such as a numeric expression whose
default scale indicator was neither `u' nor `z'. 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
`gtroff' 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.
- Register: \n[.ps]
A read-only number register returning the point size in scaled
points.
`.ps' is associated with the current environment (*note
Environments::).
- Register: \n[.psr]
- Register: \n[.sr]
The last-requested point size in scaled points is contained in the
`.psr' read-only number register. The last requested point size
in points as a decimal fraction can be found in `.sr'. This is a
string-valued read-only number register.
Note that the requested point sizes are device-independent, whereas
the values returned by the `.ps' and `.s' registers are not. For
example, if a point size of 11pt is requested, and a `sizes'
request (or a `sizescale' line in a `DESC' file) specifies 10.95pt
instead, this value is actually used.
Both registers are associated with the current environment (*note
Environments::).
The `\s' escape has the following syntax for working with fractional
type sizes:
`\s[N]'
`\s'N''
Set the point size to N scaled points; N is a numeric expression
with a default scale indicator of `z'.
`\s[+N]'
`\s[-N]'
`\s+[N]'
`\s-[N]'
`\s'+N''
`\s'-N''
`\s+'N''
`\s-'N''
Increase or or decrease the point size by N scaled points; N is a
numeric expression with a default scale indicator of `z'.
*Note Font Files::.

File: groff, Node: Strings, Next: Conditionals and Loops, Prev: Sizes, Up: gtroff Reference
Strings
=======
`gtroff' has string variables, which are entirely for user
convenience (i.e. there are no built-in strings exept `.T', but even
this is a read-write string variable).
- Request: .ds name [string]
- Request: .ds1 name [string]
- Escape: \*n
- Escape: \*(nm
- Escape: \*[name arg1 arg2 ...]
Define and access a string variable NAME (one-character name N,
two-character name NM). If NAME already exists, `ds' overwrites
the previous definition. Only the syntax form using brackets can
take arguments which are handled identically to macro arguments;
the single exception is that a closing bracket as an argument must
be enclosed in double quotes. *Note Request and Macro
Arguments::, and *Note Parameters::.
Example:
.ds foo a \\$1 test
.
This is \*[foo nice].
=> This is a nice test.
The `\*' escape "interpolates" (expands in-place) a
previously-defined string variable. To be more precise, the stored
string is pushed onto the input stack which is then parsed by
`gtroff'. Similar to number registers, it is possible to nest
strings, i.e. string variables can be called within string
variables.
If the string named by the `\*' escape does not exist, it is
defined as empty, and a warning of type `mac' is emitted (see
*Note Debugging::, for more details).
*Caution:* Unlike other requests, the second argument to the `ds'
request takes up the entire line including trailing spaces. This
means that comments on a line with such a request can introduce
unwanted space into a string.
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d \" UNIX trademark
Instead the comment should be put on another line or have the
comment escape adjacent with the end of the string.
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d\" UNIX trademark
To produce leading space the string can be started with a double
quote. No trailing quote is needed; in fact, any trailing quote is
included in your string.
.ds sign " Yours in a white wine sauce,
Strings are not limited to a single line of text. A string can
span several lines by escaping the newlines with a backslash. The
resulting string is stored _without_ the newlines.
.ds foo lots and lots \
of text are on these \
next several lines
It is not possible to have real newlines in a string. To put a
single double quote character into a string, use two consecutive
double quote characters.
The `ds1' request turns off compatibility mode while interpreting
a string. To be more precise, a "compatibility save" input token
is inserted at the beginning of the string, and a "compatibility
restore" input token at the end.
.nr xxx 12345
.ds aa The value of xxx is \\n[xxx].
.ds1 bb The value of xxx ix \\n[xxx].
.
.cp 1
.
\*(aa
=> warning: number register `[' not defined
=> The value of xxx is 0xxx].
\*(bb
=> The value of xxx ix 12345.
Strings, macros, and diversions (and boxes) share the same name
space. Internally, even the same mechanism is used to store them.
This has some interesting consequences. For example, it is
possible to call a macro with string syntax and vice versa.
.de xxx
a funny test.
..
This is \*[xxx]
=> This is a funny test.
.ds yyy a funny test
This is
.yyy
=> This is a funny test.
Diversions and boxes can be also called with string syntax.
Another consequence is that you can copy one-line diversions or
boxes to a string.
.di xxx
a \fItest\fR
.br
.di
.ds yyy This is \*[xxx]\c
\*[yyy].
=> This is a test.
As the previous example shows, it is possible to store formatted
output in strings. The `\c' escape prevents the insertion of an
additional blank line in the output.
Copying diversions longer than a single output line produces
unexpected results.
.di xxx
a funny
.br
test
.br
.di
.ds yyy This is \*[xxx]\c
\*[yyy].
=> test This is a funny.
Usually, it is not predictable whether a diversion contains one or
more output lines, so this mechanism should be avoided. With UNIX
`troff', this was the only solution to strip off a final newline
from a diversion. Another disadvantage is that the spaces in the
copied string are already formatted, making them unstretchable.
This can cause ugly results.
A clean solution to this problem is available in GNU `troff',
using the requests `chop' to remove the final newline of a
diversion, and `unformat' to make the horizontal spaces
stretchable again.
.box xxx
a funny
.br
test
.br
.box
.chop xxx
.unformat xxx
This is \*[xxx].
=> This is a funny test.
*Note Gtroff Internals::, for more information.
- Request: .as name [string]
- Request: .as1 name [string]
The `as' request is similar to `ds' but appends STRING to the
string stored as NAME instead of redefining it. If NAME doesn't
exist yet, it is created.
.as sign " with shallots, onions and garlic,
The `as1' request is similar to `as', but compatibility mode is
switched off while the appended string is interpreted. To be more
precise, a "compatibility save" input token is inserted at the
beginning of the appended string, and a "compatibility restore"
input token at the end.
Rudimentary string manipulation routines are given with the next two
requests.
- Request: .substring str n1 [n2]
Replace the string named STR 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.
.ds xxx abcdefgh
.substring xxx 1 -4
\*[xxx]
=> bcde
- Request: .length reg str
Compute the number of characters of STR and return it in the
number register REG. If REG doesn't exist, it is created. `str'
is read in copy mode.
.ds xxx abcd\h'3i'efgh
.length yyy \*[xxx]
\n[yyy]
=> 14
- Request: .rn xx yy
Rename the request, macro, diversion, or string XX to YY.
- Request: .rm xx
Remove the request, macro, diversion, or string XX. `gtroff'
treats subsequent invocations as if the object had never been
defined.
- Request: .als new old
Create an alias named NEW for the request, string, macro, or
diversion object named OLD. The new name and the old name are
exactly equivalent (it is similar to a hard rather than a soft
link). If OLD is undefined, `gtroff' generates a warning of type
`mac' and ignores the request.
- Request: .chop xx
Remove (chop) the last character from the macro, string, or
diversion named XX. This is useful for removing the newline from
the end of diversions that are to be interpolated as strings.
This command can be used repeatedly; see *Note Gtroff Internals::,
for details on nodes inserted additionally by `gtroff'.
*Note Identifiers::, and *Note Comments::.

File: groff, Node: Conditionals and Loops, Next: Writing Macros, Prev: Strings, Up: gtroff Reference
Conditionals and Loops
======================
* Menu:
* Operators in Conditionals::
* if-else::
* while::

File: groff, Node: Operators in Conditionals, Next: if-else, Prev: Conditionals and Loops, Up: Conditionals and Loops
Operators in Conditionals
-------------------------
In `if' and `while' requests, there are several more operators
available:
`e'
`o'
True if the current page is even or odd numbered (respectively).
`n'
True if the document is being processed in nroff mode (i.e., the
`.nroff' command has been issued).
`t'
True if the document is being processed in troff mode (i.e., the
`.troff' command has been issued).
`v'
Always false. This condition is for compatibility with other
`troff' versions only.
`'XXX'YYY''
True if the string XXX is equal to the string YYY. Other
characters can be used in place of the single quotes; the same set
of delimiters as for the `\D' escape is used (*note Escapes::).
`gtroff' formats the strings before being compared:
.ie "|"\fR|\fP" \
true
.el \
false
=> true
The resulting motions, glyph sizes, and fonts have to match,(1)
(*note Operators in Conditionals-Footnote-1::) and not the
individual motion, size, and font requests. In the previous
example, `|' and `\fR|\fP' both result in a roman `|' glyph with
the same point size and at the same location on the page, so the
strings are equal. If `.ft I' had been added before the `.ie',
the result would be "false" because (the first) `|' produces an
italic `|' rather than a roman one.
`r XXX'
True if there is a number register named XXX.
`d XXX'
True if there is a string, macro, diversion, or request named XXX.
`m XXX'
True if there is a color named XXX.
`c G'
True if there is a glyph G available(2) (*note Operators in
Conditionals-Footnote-2::); G is either an ASCII character or a
special character (`\(GG' or `\[GGG]'); the condition is also true
if G has been defined by the `char' request.
Note that these operators can't be combined with other operators like
`:' or `&'; only a leading `!' (without whitespace between the
exclamation mark and the operator) can be used to negate the result.
.nr xxx 1
.ie !r xxx \
true
.el \
false
=> false
A whitespace after `!' always evaluates to zero (this bizarre
behaviour is due to compatibility with UNIX `troff').
.nr xxx 1
.ie ! r xxx \
true
.el \
false
=> r xxx true
It is possible to omit the whitespace before the argument to the
`r', `d', and `c' operators.
*Note Expressions::.

File: groff, Node: Operators in Conditionals-Footnotes, Up: Operators in Conditionals
(1) The created output nodes must be identical. *Note Gtroff
Internals::.
(2) The name of this conditional operator is a misnomer since it
tests names of output glyphs.

File: groff, Node: if-else, Next: while, Prev: Operators in Conditionals, Up: Conditionals and Loops
if-else
-------
`gtroff' has if-then-else constructs like other languages, although
the formatting can be painful.
- Request: .if expr anything
Evaluate the expression EXPR, and executes ANYTHING (the remainder
of the line) if EXPR evaluates to non-zero (true). ANYTHING is
interpreted as though it was on a line by itself (except that
leading spaces are swallowed). *Note Expressions::, for more info.
.nr xxx 1
.nr yyy 2
.if ((\n[xxx] == 1) & (\n[yyy] == 2)) true
=> true
- Request: .nop anything
Executes ANYTHING. This is similar to `.if 1'.
- Request: .ie expr anything
- Request: .el anything
Use the `ie' and `el' requests to write an if-then-else. The
first request is the `if' part and the latter is the `else' part.
.ie n .ls 2 \" double-spacing in nroff
.el .ls 1 \" single-spacing in troff
- Escape: \{
- Escape: \}
In many cases, an if (or if-else) construct needs to execute more
than one request. This can be done using the `\{' and `\}'
escapes. The following example shows the possible ways to use
these escapes (note the position of the opening and closing
braces).
.ie t \{\
. ds lq ``
. ds rq ''
.\}
.el \
.\{\
. ds lq "
. ds rq "\}
*Note Expressions::.

File: groff, Node: while, Prev: if-else, Up: Conditionals and Loops
while
-----
`gtroff' provides a looping construct using the `while' request,
which is used much like the `if' (and related) requests.
- Request: .while expr anything
Evaluate the expression EXPR, and repeatedly execute ANYTHING (the
remainder of the line) until EXPR evaluates to 0.
.nr a 0 1
.while (\na < 9) \{\
\n+a,
.\}
\n+a
=> 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
Some remarks.
* The body of a `while' request is treated like the body of a
`de' request: `gtroff' temporarily stores it in a macro which
is deleted after the loop has been exited. It can
considerably slow down a macro if the body of the `while'
request (within the macro) is large. Each time the macro is
executed, the `while' body is parsed and stored again as a
temporary macro.
.de xxx
. nr num 10
. while (\\n[num] > 0) \{\
. \" many lines of code
. nr num -1
. \}
..
The traditional and ofter better solution (UNIX `troff'
doesn't have the `while' request) is to use a recursive macro
instead which is parsed only once during its definition.
.de yyy
. if (\\n[num] > 0) \{\
. \" many lines of code
. nr num -1
. yyy
. \}
..
.
.de xxx
. nr num 10
. yyy
..
Note that the number of available recursion levels is set
to 1000 (this is a compile-time constant value of `gtroff').
* The closing brace of a `while' body must end a line.
.if 1 \{\
. nr a 0 1
. while (\n[a] < 10) \{\
. nop \n+[a]
.\}\}
=> unbalanced \{ \}
- Request: .break
Break out of a `while' loop. Be sure not to confuse this with the
`br' request (causing a line break).
- Request: .continue
Finish the current iteration of a `while' loop, immediately
restarting the next iteration.
*Note Expressions::.

File: groff, Node: Writing Macros, Next: Page Motions, Prev: Conditionals and Loops, Up: gtroff Reference
Writing Macros
==============
A "macro" is a collection of text and embedded commands which can be
invoked multiple times. Use macros to define common operations.
- Request: .de name [end]
- Request: .de1 name [end]
- Request: .dei name [end]
Define a new macro named NAME. `gtroff' copies subsequent lines
(starting with the next one) into an internal buffer until it
encounters the line `..' (two dots). The optional second argument
to `de' changes this to a macro to `.END'.
There can be whitespace after the first dot in the line containing
the ending token (either `.' or macro `END').
Here a small example macro called `P' which causes a break and
inserts some vertical space. It could be used to separate
paragraphs.
.de P
. br
. sp .8v
..
The following example defines a macro within another. Remember
that expansion must be protected twice; once for reading the macro
and once for executing.
\# a dummy macro to avoid a warning
.de end
..
.
.de foo
. de bar end
. nop \f[B]Hallo \\\\$1!\f[]
. end
..
.
.foo
.bar Joe
=> Hallo Joe!
Since `\f' has no expansion, it isn't necessary to protect its
backslash. Had we defined another macro within `bar' which takes
a parameter, eight backslashes would be necessary before `$1'.
The `de1' request turns off compatibility mode while executing the
macro. On entry, the current compatibility mode is saved and
restored at exit.
.nr xxx 12345
.
.de aa
The value of xxx is \\n[xxx].
..
.de1 bb
The value of xxx ix \\n[xxx].
..
.
.cp 1
.
.aa
=> warning: number register ' not defined
=> The value of xxx is 0xxx].
.bb
=> The value of xxx ix 12345.
The `dei' request defines a macro indirectly. That is, it expands
strings whose names are NAME or END before performing the append.
This:
.ds xx aa
.ds yy bb
.dei xx yy
is equivalent to:
.de aa bb
Using `trace.tmac', you can trace calls to `de' and `de1'.
Note that macro identifiers are shared with identifiers for
strings and diversions.
- Request: .am name [end]
- Request: .am1 name [end]
- Request: .ami name [end]
Works similarly to `de' except it appends onto the macro named
NAME. So, to make the previously defined `P' macro actually do
indented instead of block paragraphs, add the necessary code to the
existing macro like this:
.am P
.ti +5n
..
The `am1' request turns off compatibility mode while executing the
appended macro piece. To be more precise, a "compatibility save"
input token is inserted at the beginning of the appended code, and
a "compatibility restore" input token at the end.
The `ami' request appends indirectly, meaning that `gtroff'
expands strings whose names are NAME or END before performing the
append.
Using `trace.tmac', you can trace calls to `am' and `am1'.
*Note Strings::, for the `als' request to rename a macro.
The `de', `am', `di', `da', `ds', and `as' requests (together with
its variants) only create a new object if the name of the macro,
diversion or string diversion is currently undefined or if it is
defined to be a request; normally they modify the value of an existing
object.
- Request: .return
Exit a macro, immediately returning to the caller.
* Menu:
* Copy-in Mode::
* Parameters::

File: groff, Node: Copy-in Mode, Next: Parameters, Prev: Writing Macros, Up: Writing Macros
Copy-in Mode
------------
When `gtroff' reads in the text for a macro, string, or diversion,
it copies the text (including request lines, but excluding escapes) into
an internal buffer. Escapes are converted into an internal form,
except for `\n', `\$', `\*', `\\' and `\<RET>' which are evaluated and
inserted into the text where the escape was located. This is known as
"copy-in" mode or "copy" mode.
What this means is that you can specify when these escapes are to be
evaluated (either at copy-in time or at the time of use) by insulating
the escapes with an extra backslash. Compare this to the `\def' and
`\edef' commands in TeX.
The following example prints the numbers 20 and 10:
.nr x 20
.de y
.nr x 10
\&\nx
\&\\nx
..
.y

File: groff, Node: Parameters, Prev: Copy-in Mode, Up: Writing Macros
Parameters
----------
The arguments to a macro or string can be examined using a variety of
escapes.
- Register: \n[.$]
The number of arguments passed to a macro or string. This is a
read-only number register.
Any individual argument can be retrieved with one of the following
escapes:
- Escape: \$n
- Escape: \$(nn
- Escape: \$[nnn]
Retrieve the Nth, NNth or NNNth argument. As usual, the first
form only accepts a single number (larger than zero), the second a
two-digit number (larger or equal to 10), and the third any
positive integer value (larger than zero). Macros and strings can
have an unlimited number of arguments. Note that due to copy-in
mode, use two backslashes on these in actual use to prevent
interpolation until the macro is actually invoked.
- Request: .shift [n]
Shift the arguments 1 position, or as many positions as specified
by its argument. After executing this request, argument I becomes
argument I-N; arguments 1 to N are no longer available. Shifting
by negative amounts is currently undefined.
- Escape: \$*
- Escape: \$@
In some cases it is convenient to use all of the arguments at once
(for example, to pass the arguments along to another macro). The
`\$*' escape concatenates all the arguments separated by spaces. A
similar escape is `\$@', which concatenates all the arguments with
each surrounded by double quotes, and separated by spaces. If not
in compatibility mode, the input level of double quotes is
preserved (see *Note Request and Macro Arguments::).
- Escape: \$0
The name used to invoke the current macro. The `als' request can
make a macro have more than one name.
.de generic-macro
. ...
. if \\n[error] \{\
. tm \\$0: Houston, we have a problem.
. return
. \}
..
.
.als foo generic-macro
.als bar generic-macro
*Note Request and Macro Arguments::.

File: groff, Node: Page Motions, Next: Drawing Requests, Prev: Writing Macros, Up: gtroff Reference
Page Motions
============
*Note Manipulating Spacing::, for a discussion of the main request
for vertical motion, `sp'.
- Request: .mk [reg]
- Request: .rt [dist]
The request `mk' can be used to mark a location on a page, for
movement to later. This request takes a register name as an
argument in which to store the current page location. With no
argument it stores the location in an internal register. The
results of this can be used later by the `rt' or the `sp' request
(or the `\v' escape).
The `rt' request returns _upwards_ to the location marked with the
last `mk' request. If used with an argument, return to a position
which distance from the top of the page is DIST (no previous call
to `mk' is necessary in this case). Default scaling indicator is
`v'.
Here a primitive solution for a two-column macro.
.nr column-length 1.5i
.nr column-gap 4m
.nr bottom-margin 1m
.
.de 2c
. br
. mk
. ll \\n[column-length]u
. wh -\\n[bottom-margin]u 2c-trap
. nr right-side 0
..
.
.de 2c-trap
. ie \\n[right-side] \{\
. nr right-side 0
. po -(\\n[column-length]u + \\n[column-gap]u)
. \" remove trap
. wh -\\n[bottom-margin]u
. \}
. el \{\
. \" switch to right side
. nr right-side 1
. po +(\\n[column-length]u + \\n[column-gap]u)
. rt
. \}
..
.
.pl 1.5i
.ll 4i
This is a small test which shows how the
rt request works in combination with mk.
.2c
Starting here, text is typeset in two columns.
Note that this implementation isn't robust
and thus not suited for a real two-column
macro.
Result:
This is a small test which shows how the
rt request works in combination with mk.
Starting here, isn't robust
text is typeset and thus not
in two columns. suited for a
Note that this real two-column
implementation macro.
The following escapes give fine control of movements about the page.
- Escape: \v'e'
Move vertically, usually from the current location on the page (if
no absolute position operator `|' is used). The argument E
specifies the distance to move; positive is downwards and negative
upwards. The default scaling indicator for this escape is `v'.
Beware, however, that `gtroff' continues text processing at the
point where the motion ends, so you should always balance motions
to avoid interference with text processing.
`\v' doesn't trigger a trap. This can be quite useful; for
example, consider a page bottom trap macro which prints a marker
in the margin to indicate continuation of a footnote or something
similar.
There are some special-case escapes for vertical motion.
- Escape: \r
Move upwards 1v.
- Escape: \u
Move upwards .5v.
- Escape: \d
Move down .5v.
- Escape: \h'e'
Move horizontally, usually from the current location (if no
absolute position operator `|' is used). The expression E
indicates how far to move: positive is rightwards and negative
leftwards. The default scaling indicator for this escape is `m'.
This horizontal space is not discarded at the end of a line. To
insert discardable space of a certain length use the `ss' request.
There are a number of special-case escapes for horizontal motion.
- Escape: \<SP>
An unbreakable and unpaddable (i.e. not expanded during filling)
space. (Note: This is a backslash followed by a space.)
- Escape: \~
An unbreakable space that stretches like a normal inter-word space
when a line is adjusted.
- Escape: \|
A 1/6th em space. Ignored for TTY output devices (rounded to
zero).
- Escape: \^
A 1/12th em space. Ignored for TTY output devices (rounded to
zero).
- Escape: \0
A space the size of a digit.
The following string sets the TeX logo:
.ds TeX T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X
- Escape: \w'text'
- Register: \n[st]
- Register: \n[sb]
- Register: \n[rst]
- Register: \n[rsb]
- Register: \n[ct]
- Register: \n[ssc]
- Register: \n[skw]
Return the width of the specified TEXT in basic units. This
allows horizontal movement based on the width of some arbitrary
text (e.g. given as an argument to a macro).
The length of the string `abc' is \w'abc'u.
=> The length of the string `abc' is 72u.
Font changes may occur in TEXT which don't affect current settings.
After use, `\w' sets several registers:
`st'
`sb'
The highest and lowest point of the baseline, respectively,
in TEXT.
`rst'
`rsb'
Like the `st' and `sb' registers, but takes account of the
heights and depths of glyphs. With other words, this gives
the highest and lowest point of TEXT. Values below the
baseline are negative.
`ct'
Defines the kinds of glyphs occurring in TEXT:
0
only short glyphs, no descenders or tall glyphs.
1
at least one descender.
2
at least one tall glyph.
3
at least one each of a descender and a tall glyph.
`ssc'
The amount of horizontal space (possibly negative) that
should be added to the last glyph before a subscript.
`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.
- Escape: \kp
- Escape: \k(ps
- Escape: \k[position]
Store the current horizontal position in the _input_ line in
number register with name POSITION (one-character name P,
two-character name PS). Use this, for example, to return to the
beginning of a string for highlighting or other decoration.
- Register: \n[hp]
The current horizontal position at the input line.
- Register: \n[.k]
A read-only number register containing the current horizontal
output position.
- Escape: \o'abc'
Overstrike glyphs A, B, C, ...; the glyphs are centered, and the
resulting spacing is the largest width of the affected glyphs.
- Escape: \zg
Print glyph G with zero width, i.e., without spacing. Use this to
overstrike glyphs left-aligned.
- Escape: \Z'anything'
Print ANYTHING, then restore the horizontal and vertical position.
The argument may not contain tabs or leaders.
The following is an example of a strike-through macro:
.de ST
.nr ww \w'\\$1'
\Z@\v'-.25m'\l'\\n[ww]u'@\\$1
..
.
This is
.ST "a test"
an actual emergency!

File: groff, Node: Drawing Requests, Next: Traps, Prev: Page Motions, Up: gtroff Reference
Drawing Requests
================
`gtroff' provides a number of ways to draw lines and other figures
on the page. Used in combination with the page motion commands (see
*Note Page Motions::, for more info), a wide variety of figures can be
drawn. However, for complex drawings these operations can be quite
cumbersome, and it may be wise to use graphic preprocessors like `gpic'
or `ggrn'. *Note gpic::, and *Note ggrn::, for more information.
All drawing is done via escapes.
- Escape: \l'l'
- Escape: \l'lg'
Draw a line horizontally. L is the length of the line to be
drawn. If it is positive, start the line at the current location
and draw to the right; its end point is the new current location.
Negative values are handled differently: The line starts at the
current location and draws to the left, but the current location
doesn't move.
L can also be specified absolutely (i.e. with a leading `|') which
draws back to the beginning of the input line. Default scaling
indicator is `m'.
The optional second parameter G is a glyph to draw the line with.
If this second argument is not specified, `gtroff' uses the
underscore glyph, `\[ru]'.
To separate the two arguments (to prevent `gtroff' from
interpreting a drawing glyph as a scaling indicator if the glyph is
represented by a single character) use `\&'.
Here a small useful example:
.de box
\[br]\\$*\[br]\l'|0\[rn]'\l'|0\[ul]'
..
Note that this works by outputting a box rule (a vertical line),
then the text given as an argument and then another box rule.
Finally, the line drawing escapes both draw from the current
location to the beginning of the _input_ line - this works because
the line length is negative, not moving the current point.
- Escape: \L'l'
- Escape: \L'lg'
Draw vertical lines. Its parameters are similar to the `\l'
escape, except that the default scaling indicator is `v'. The
movement is downwards for positive values, and upwards for
negative values. The default glyph is the box rule glyph,
`\[br]'. As with the vertical motion escapes, text processing
blindly continues where the line ends.
This is a \L'3v'test.
Here the result, produced with `grotty'.
This is a
|
|
|test.
- Escape: \D'command arg ...'
The `\D' escape provides a variety of drawing functions. Note
that on character devices, only vertical and horizontal lines are
supported within `grotty'; other devices may only support a subset
of the available drawing functions.
The default scaling indicator for all subcommands of `\D' is `m'
for horizontal distances and `v' for vertical ones. Exceptions
are `\D'f ...'' and `\D't ...'' which use `u' as the default, and
`\D'FX ...'' which arguments are treated similar to the `defcolor'
request.
`\D'l DX DY''
Draw a line from the current location to the relative point
specified by (DX,DY).
The following example is a macro for creating a box around a
text string; for simplicity, the box margin is taken as a
fixed value, 0.2m.
.de BOX
. nr @wd \w'\\$1'
\h'.2m'\
\h'-.2m'\v'(.2m - \\n[rsb]u)'\
\D'l 0 -(\\n[rst]u - \\n[rsb]u + .4m)'\
\D'l (\\n[@wd]u + .4m) 0'\
\D'l 0 (\\n[rst]u - \\n[rsb]u + .4m)'\
\D'l -(\\n[@wd]u + .4m) 0'\
\h'.2m'\v'-(.2m - \\n[rsb]u)'\
\\$1\
\h'.2m'
..
First, the width of the string is stored in register `@wd'.
Then, four lines are drawn to form a box, properly offset by
the box margin. The registers `rst' and `rsb' are set by the
`\w' escape, containing the largest height and depth of the
whole string.
`\D'c D''
Draw a circle with a diameter of D with the leftmost point at
the current position. After drawing, the current location is
positioned at the rightmost point of the circle.
`\D'C D''
Draw a solid circle with the same parameters and behaviour as
an outlined circle. No outline is drawn.
`\D'e X Y''
Draw an ellipse with a horizontal diameter of X and a vertical
diameter of Y with the leftmost point at the current position.
After drawing, the current location is positioned at the
rightmost point of the ellipse.
`\D'E X Y''
Draw a solid ellipse with the same parameters and behaviour
as an outlined ellipse. No outline is drawn.
`\D'a DX1 DY1 DX2 DY2''
Draw an arc clockwise from the current location through the
two specified relative locations (DX1,DY1) and (DX2,DY2).
The coordinates of the first point are relative to the
current position, and the coordinates of the second point are
relative to the first point. After drawing, the current
position is moved to the final point of the arc.
`\D'~ DX1 DY1 DX2 DY2 ...''
Draw a spline from the current location to the relative point
(DX1,DY1) and then to (DX2,DY2), and so on. The current
position is moved to the terminal point of the drawn curve.
`\D'f 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.
Despite of being silly, the current point is moved
horizontally to the right by N.
Don't use this command! It has the serious drawback that it
will be always rounded to the next integer multiple of the
horizontal resolution (the value of the `hor' keyword in the
`DESC' file). Use `\M' (*note Colors::) or `\D'Fg ...''
instead.
`\D'p DX1 DY1 DX2 DY2 ...''
Draw a polygon from the current location to the relative
position (DX1,DY1) and then to (DX2,DY2) and so on. When the
specified data points are exhausted, a line is drawn back to
the starting point. The current position is changed by
adding the sum of all arguments with odd index to the actual
horizontal position and the even ones to the vertical
position.
`\D'P DX1 DY1 DX2 DY2 ...''
Draw a solid polygon with the same parameters and behaviour
as an outlined polygon. No outline is drawn.
Here a better variant of the box macro to fill the box with
some color. Note that the box must be drawn before the text
since colors in `gtroff' are not transparent; the filled
polygon would hide the text completely.
.de BOX
. nr @wd \w'\\$1'
\h'.2m'\
\h'-.2m'\v'(.2m - \\n[rsb]u)'\
\M[lightcyan]\
\D'P 0 -(\\n[rst]u - \\n[rsb]u + .4m) \
(\\n[@wd]u + .4m) 0 \
0 (\\n[rst]u - \\n[rsb]u + .4m) \
-(\\n[@wd]u + .4m) 0'\
\h'.2m'\v'-(.2m - \\n[rsb]u)'\
\M[]\
\\$1\
\h'.2m'
..
`\D't N''
Set the current line thickness to N machine units. A value of
zero selects the smallest available line thickness. A
negative value makes the line thickness proportional to the
current point size (this is the default behaviour of AT&T
`troff').
Despite of being silly, the current point is moved
horizontally to the right by N.
`\D'FSCHEME COLOR_COMPONENTS''
Change current fill color. SCHEME is a single letter
denoting the color scheme: `r' (rgb), `c' (cmy), `k' (cmyk),
`g' (gray), or `d' (default color). The color components use
exactly the same syntax as in the `defcolor' request (*note
Colors::); the command `\D'Fd'' doesn't take an argument.
_No_ position changing!
Examples:
\D'Fg .3' \" same gray as \D'f 700' \D'Fr #0000ff' \"
blue
*Note Graphics Commands::.
- Escape: \b'string'
"Pile" a sequence of glyphs vertically, and center it vertically
on the current line. Use it to build large brackets and braces.
Here an example how to create a large opening brace:
\b'\[lt]\[bv]\[lk]\[bv]\[lb]'
The first glyph is on the top, the last glyph in STRING is at the
bottom. Note that `gtroff' separates the glyphs vertically by 1m,
and the whole object is centered 0.5m above the current baseline;
the largest glyph width is used as the width for the whole object.
This rather unflexible positioning algorithm doesn't work with
`-Tdvi' since the bracket pieces vary in height for this device.
Instead, use the `eqn' preprocessor.
*Note Manipulating Spacing::, how to adjust the vertical spacing
with the `\x' escape.

File: groff, Node: Traps, Next: Diversions, Prev: Drawing Requests, Up: gtroff Reference
Traps
=====
"Traps" are locations, which, when reached, call a specified macro.
These traps can occur at a given location on the page, at a given
location in the current diversion, at a blank line, after a certain
number of input lines, or at the end of input.
Setting a trap is also called "planting". It is also said that a
trap is "sprung" if the associated macro is executed.
* Menu:
* Page Location Traps::
* Diversion Traps::
* Input Line Traps::
* Blank Line Traps::
* End-of-input Traps::
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