Default Operation of Requests (UNIX in a Nutshell: System V Edition)

12.4. Default Operation of Requests

nroff/troff initializes the formatting environment. For example, unless you reset the line length, nroff/troff uses 6.5 inches. Most requests can change the default environment, and those that can are listed in Table 12-1. The second column lists the initial or default value in effect before the request is used. If no initial value applies, a hyphen (–) is used. The third column shows the effect if a request's optional argument is not used. Here, a hyphen is used if the request doesn't accept an argument or if the argument is required.

Table 12-1. Requests That Affect the Default Environment

Request	Initial Value	If No Argument	Description
`.ad`	Justify	Justify	Adjust margins.
`.af`	Lowercase arabic	–	Assign a format to a register.
`.am`	–	End call with `..`	Append to a macro.
`.bd`	Off	–	Embolden font.
`.c2`	`'`	`'`	Set no-break control character.
`.cc`	`.`	`.`	Set control character.
`.ce`	Off	Center one line	Center lines.
`.ch`	–	Turn off trap	Change trap position.
`.cs`	Off	–	Set constant-width spacing.
`.cu`	Off	One line	Continuous underline/italicize.
`.da`	–	End the diversion	Divert text and append to a macro.
`.de`	–	End macro with `..`	Define a macro.
`.di`	–	End the diversion	Divert text to a macro.
`.dt`	–	Turn off trap	Set a diversion trap.
`.ec`	\	\	Set escape character.
`.eo`	On	–	Turn off escape character.
`.ev`	0	Previous environment	Change environment (push down).
`.fc`	Off	Off	Set field delimiter and pad character.
`.fi`	Fill	–	Fill lines.
`.fp`	1=R 2=I 3=B 4=S	–	Mount font (on positions 1–4).
`.ft`	Roman	Previous font	Set font.
`.hc`	`\%`	`\%`	Set hyphenation character.
`.hy`	Mode 1	Mode 1	Set hyphenation mode.
`.ig`	–	End with `..`	Suppress (ignore) text in output.
`.in`	0	Previous indent	Indent.
`.it`	–	Turn off trap	Set a trap for input line counting.
`.lc`	`.`	None	Set leader character.
`.lg`	Off (`nroff`) On (`troff`)	On	Ligature mode.
`.ll`	6.5 inches	Previous line length	Set line length.
`.ls`	Single-space	Previous mode	Set line spacing.
`.lt`	6.5 inches	Previous title length	Set length of title.
`.mc`	–	Turn off	Set the margin character.
`.mk`	–	Internal	Mark vertical position.
`.na`	Adjust	–	Don't adjust margins.
`.ne`	–	One vertical line	Keep lines on same page if there's room.
`.nf`	Fill	–	Don't fill lines.
`.nh`	On	–	Turn off hyphenation.
`.nm`	Off	Off	Line-numbering mode.
`.nn`	–	One line	Don't number next N lines.
`.ns`	Space mode	–	Enable no-space mode.
`.nx`	–	End of file	Go to a file.
`.pc`	`%`	Off	Set page character.
`.pl`	11 inches	11 inches	Set page length.
`.pn`	Page 1	–	Set page number.
`.po`	0 (`nroff`); 26/27 inch (`otroff`) 1 inch (`ditroff`)	Previous offset	Change page offset.
`.ps`	10	Previous point size	Set point size.
`.rd`	–	Ring bell	Read from the terminal.
`.rt`	–	Internal	Return to marked vertical place.
`.sp`	–	One vertical line	Output blank spacing.
`.ss`	12/36 em	Ignored	Set character spacing.
`.sv`	–	One vertical line	Save (store) spacing.
`.ta`	8 en (`nroff`); 1/2 inch (`troff`)	–	Define tab settings.
`.tc`	–	–	Set tab repetition character.
`.ti`	0	–	Indent next line.
`.tm`	–	Newline	Print a message, then continue.
`.tr`	–	–	Translate pairs of characters on output.
`.uf`	Italic	Italic	Set font for underlining.
`.ul`	0	One line	Underline/italicize.
`.vs`	1/6 inch (`nroff`); 12 points (`troff`)	Previous value	Set vertical spacing for lines.

Comments in nroff/troff begin with \". Lines beginning with . that contain an unknown request are ignored. In general, don't put leading whitespace on your text lines. This causes a break, and nroff and troff honors the leading whitespace literally.

Note: the canonical reference for nroff/troff is Bell Labs Computing Science Technical Report #54, Troff User's Manual, by J.F. Ossanna and B.W. Kernighan. It is available in PostScript from http://cm.bell-labs.com/cm/cs/cstr/54.ps.gz. You should read it if you plan to do any serious work in nroff/troff (such as writing or modifying macro packages). This document explains the ideas of diversions, environments, fields, registers, strings, and traps.