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12.8. Predefined Registers

There are two types of predefined registers: read-only and read-write. These are all accessed via the \n escape sequence, even though some of them actually return string values.

12.8.1. Read-Only Registers


Number of arguments available at the current macro level.

$$Process ID of troff process (ditroff only).

Set to 1 in troff, if -a option used; always 1 in nroff.


Name of the current input file (recent ditroff only).

.HAvailable horizontal resolution in basic units.

Current line spacing (set by .ls) value (recent ditroff only).


Number of unused number registers (recent ditroff only).


Set to 1 in nroff, if -T option used; always 0 in oroff; in ditroff, the string \*(.T contains the value of -T.

.VAvailable vertical resolution in basic units.

Post-line extra line space most recently utilized using \x'n'.


Emboldening level (recent ditroff only).

.cNumber of lines read from current input file.

Current vertical place in current diversion; equal to register nl when there is no diversion.


Current font as number (1 to 4 in otroff; 1 to 99 in ditroff).

.hText baseline high-water mark on current page or diversion.
.iCurrent indent.
.jCurrent adjustment mode.

Current output horizontal position.

.lCurrent line length.
.nLength of text portion on previous output line.
.oCurrent page offset.
.pCurrent page length.
.sCurrent point size.
.tDistance to the next trap.
.uEqual to 1 in fill mode and 0 in no-fill mode.
.vCurrent vertical line spacing.
.wWidth of previous character.
.xReserved version-dependent register.
.yReserved version-dependent register.
.zName of current diversion.

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