[Chapter 12] 12.8 Predefined Number Registers
Author: Daniel Gilly & the Staff of O'Reilly & Associates
Date: 1998-08-06T22:00:59Z

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| Chapter 12 Nroff and Troff |

## 12.8 Predefined Number Registers

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

### 12.8.1 Read-only Registers

.$ | 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.

### 12.8.2 Read-write Registers

% | 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.

12.7 Escape Sequences |  | 12.9 Special Characters