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12.3. Conceptual Overview
This sections provides a brief overview of how to prepare input for nroff and troff. It presents the following topics:
Requests and macros
Common requests
Specifying measurements
Requests that cause a line break
Embedded formatting controls
12.3.1. Requests and Macros
Formatting is specified by embedding brief codes (called requests) into the text source file. These codes act as directives to nroff and troff when they run. For example, to center a line of text, type the following code in a file:
.ce This text should be centered.
When formatted, the output appears centered:
This text should be centered.
There are two types of formatting codes:
Requests, which provide the most elementary instructions
Macros, which are predefined combinations of requests
Requests, also known as primitives, allow direct control of almost any feature of page layout and formatting. Macros combine requests to create a total effect. In a sense, requests are like atoms, and macros are like molecules.
All nroff/troff requests are two-letter lowercase names. Macros are usually upper- or mixed-case names.
See Chapter 13, Chapter 14, Chapter 15, and Chapter 16, for more information on the standard macro packages.
12.3.2. Common Requests
The most commonly used requests are:
.ad .ds .ll .nr .sp .br .fi .na .po .ta .bp .ft .ne .ps .ti .ce .in .nf .so .vs .de .ls
For example, a simple macro could be written as follows:
. \" Ps macro - show literal text display .de Ps \" Define a macro named "Ps" .sp .5 \" Space down half a line .in 1i \" Indent one inch .ta 10n +10n \" Set new tabstops .ps 8 \" Use 8-point type .vs 10 \" Use 10-point vertical spacing .ft CW \" Use constant width font .br \" Break line (.ne begins count on next line) .ne 3 \" Keep 3 lines together .nf \" No-fill mode (output lines as is) .. \" End macro definition
12.3.3. Specifying Measurements
With some requests, the numeric argument can be followed by a scale indicator that specifies a unit of measurement. The valid indicators and their meanings are listed in the following table. Note that all measurements are internally converted to basic units (this conversion is shown in the last column). A basic unit is the smallest possible size on the printer device. The device resolution (e.g., 600 dots per inch) determines the size of a basic unit. Also, T specifies the current point size, and R specifies the device resolution.
Scale Indicator | Meaning | Equivalent Unit | # of Basic Units |
|---|---|---|---|
| c | Centimeter | 2.54 inches | R / 2.54 |
| i | Inch | 6 picas or 72 points | R |
| m | Em | T points | R × T / 72 |
| n | En | 0.5 em | R × T / 144 |
| p | Point | 1/72 inch | R / 72 |
| P | Pica | 1/6 inch | R / 6 |
| u | Basic unit | 1 | |
| v | Vertical line space | (Current value in basic units) | |
| None | Default |
It is worth noting that all numbers in nroff/troff are stored internally using integers. This applies even to apparently fractional values in commands such as:
which spaces down one-half of the current vertical spacing..sp .5
An “em” is the width of the letter “m” in the current font and point size. An “en” is the width of the letter “n” in the current font and point size. Note that in nroff, an “em” and an “en” are the same--the width of one character.
You can specify a scale indicator for any of the requests in the following table, except for .ps, which always uses points. If no unit is given, the default unit is used. (The second column lists the scale indicators as described in the previous table.) For horizontally oriented requests, the default unit is ems. For vertically oriented requests, the default is usually vertical lines.
| Request | Default Scale | Request | Default Scale |
|---|---|---|---|
| .ch | v | .pl | v |
| .dt | v | .po | v |
| .ie | u | .ps | p |
| .if | u | .rt | v |
| .in | m | .sp | v |
| .ll | m | .sv | v |
| .lt | m | .ta | m |
| .mc | m | .ti | m |
| .ne | v | .vs | p |
| .nr | u | .wh | v |
12.3.4. Requests That Cause a Line Break
A line break occurs when nroff/troff writes the current output line, even if it is not completely filled. Most requests can be interspersed with text without causing a line break in the output. The following requests cause a break:
.bp .ce .fi .in .sp .br .cf .fl .nf .ti
If you need to prevent these requests from causing a break, begin them with the “no break” control character (normally ') instead of a dot (.). For example, .sp takes effect right away, but 'sp waits until the output line is completely filled. Only then does it add a line space.
12.3.5. Embedded Formatting Controls
In addition to requests and macros, which are written on their own separate lines, you may also have formatting controls embedded within your text lines. These typically provide the following capabilities:
- General formatting
- Considerable formatting control is available,
such as switching fonts (\f),
changing point sizes (\s),
computing widths (\w),
and many other things. For example:
This text is in \fIitalic\fR, but this is in roman. This text is \s-2VERY SMALL\s0 but this text is not.
- Special characters
- Predefined special typesetting characters, such as
the bullet symbol \(bu (
),
the left hand \(lh (
),
and the right hand \(rh (
).
- Strings
- User-defined sequences of characters, like macros, but usable
inline. For example:
.\" define a shorthand for UNIX .ds UX the \s-1UNIX\s0 Operating System ... Welcome to \*(UX. While \*(UX may appear daunting at first, it is immensely powerful. ...
- Number registers
- Like variables in programming languages,
number registers store numeric values that can be printed in
a range of formats (decimal, roman, etc.).
They can be set to auto-increment or auto-decrement,
and are particularly useful when writing macro packages,
for managing automatic numbering of headings, footnotes,
figures, and so on. For example:
.nr Cl 0 1 \" Chapter Level .de CH .bp \\n+(Cl. \\$1 \\$2 \\$3 ..
This creates a macro that uses register Cl as the “chapter level.” The first three arguments to the macro become the chapter title. The extra backslashes are needed inside the macro definition.
Later sections in this chapter describe the predefined special characters, strings and number registers, and all of the escape sequences that are available.
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| 12.2. Command-Line Invocation |  | 12.4. Default Operation of Requests |
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