[Chapter 12] 12.8 Predefined Number Registers

12.8 Predefined Number Registers

There are two types of predefined registers: read-only and read-write.

.$	Number of arguments available at the current macro level.
.$$	Process id of troff process (ditroff only).
.A	Set to 1 in troff, if -a option used; always 1 in nroff.
.H	Available horizontal resolution in basic units.
.T	Set to 1 in nroff, if -T option used; always 0 in troff; in ditroff, the string `\*(.T` contains the value of -T .
.V	Available vertical resolution in basic units.
.a	Post-line extra line-space most recently utilized using \x'`n` '.
.c	Number of lines read from current input file.
.d	Current vertical place in current diversion; equal to register nl when there is no diversion.
.f	Current font as physical quadrant (1 to 4 in otroff; 1 to 9 in ditroff).
.h	Text baseline high-water mark on current page or diversion.
.i	Current indent.
.j	Current adjustment mode.
.l	Current line length.
.n	Length of text portion on previous output line.
.o	Current page offset.
.p	Current page length.
.s	Current point size.
.t	Distance to the next trap.
.u	Equal to 1 in fill mode and 0 in no-fill mode.
.v	Current vertical line spacing.
.w	Width of previous character.
.x	Reserved version-dependent register.
.y	Reserved version-dependent register.
.z	Name of current diversion.

%	Current page number.
ct	Character type (set by `width` function).
dl	Width (maximum) of last completed diversion.
dn	Height (vertical size) of last completed diversion.
dw	Current day of the week (1 to 7).
dy	Current day of the month (1 to 31).
hp	Current horizontal place on `input` line.
ln	Output line number.
mo	Current month (1 to 12).
nl	Vertical position of last printed text baseline.
sb	Depth of string below baseline (generated by `width` function).
st	Height of string above base line (generated by `width` function).
yr	Last two digits of current year.