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The following lists some built-in registers that are not described elsewhere in this manual. Any register that begins with a ‘.’ is read-only. A complete listing of all built-in registers can be found in Register Index.
\n[.F]This string-valued register returns the current input file name.
\n[.H]Horizontal resolution in basic units.
\n[.R]The number of number registers available. This is always 10000 in
GNU troff; it exists for backward compatibility.
\n[.U]If gtroff is called with the -U command line option to
activate unsafe mode, the number register .U is set to 1,
and to zero otherwise. See Groff Options.
\n[.V]Vertical resolution in basic units.
\n[seconds]The number of seconds after the minute, normally in the range 0
to 59, but can be up to 61 to allow for leap seconds.
Initialized at start-up of gtroff.
\n[minutes]The number of minutes after the hour, in the range 0 to 59.
Initialized at start-up of gtroff.
\n[hours]The number of hours past midnight, in the range 0 to 23.
Initialized at start-up of gtroff.
\n[dw]Day of the week (1-7).
\n[dy]Day of the month (1-31).
\n[mo]Current month (1-12).
\n[year]The current year.
\n[yr]The current year minus 1900. Unfortunately, the documentation of
UNIX Version 7’s troff had a year 2000 bug:
It incorrectly claimed that yr contains the last two digits of
the year. That claim has never been true of either AT&T
troff or GNU troff. Old troff input that looks
like this:
'\" The following line stopped working after 1999 This document was formatted in 19\n(yr.
can be corrected as follows:
This document was formatted in \n[year].
or, to be portable to older troff versions, as follows:
.nr y4 1900+\n(yr This document was formatted in \n(y4.
\n[.c]\n[c.]The current input line number. Register ‘.c’ is read-only,
whereas ‘c.’ (a gtroff extension) is writable also,
affecting both ‘.c’ and ‘c.’.
\n[ln]The current output line number after a call to the nm
request to activate line numbering.
See Miscellaneous, for more information about line numbering.
\n[.x]The major version number. For example, if the version number is 1.03
then .x contains ‘1’.
\n[.y]The minor version number. For example, if the version number is 1.03
then .y contains ‘03’.
\n[.Y]The revision number of groff.
\n[$$]The process ID of gtroff.
\n[.g]Always 1. Macros should use this to determine whether they are
running under GNU troff.
\n[.A]If the command line option -a is used to produce an ASCII approximation of the output, this is set to 1, zero otherwise. See Groff Options.
\n[.O]This read-only register is set to the suppression nesting level (see
escapes \O). See Suppressing output.
\n[.P]This register is set to 1 (and to 0 otherwise) if the current page is actually being printed, i.e., if the -o option is being used to only print selected pages. See Groff Options, for more information.
\n[.T]If gtroff is called with the -T command line option, the
number register .T is set to 1, and zero otherwise.
See Groff Options.
\*[.T]A single read-write string register that contains the current output
device (for example, ‘latin1’ or ‘ps’). This is the only
string register defined by gtroff.
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