(groff.info)Built-in Registers

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5.6.5 Built-in Registers
------------------------

The following lists some built-in registers which are not described
elsewhere in this manual.  Any register which begins with a `.' is
read-only.  A complete listing of all built-in registers can be found in
Note: Register Index.

`\n[.F]'
     This string-valued register returns the current input file name.

`\n[.H]'
     Horizontal resolution in basic units.

`\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.  Note: 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.

     Note: 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.
     Note: Groff Options.

`\n[.O]'
     This read-only register is set to the suppression nesting level
     (see escapes `\O').  Note: 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.  Note: 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.  Note: Groff
     Options.

`\*[.T]'
     A single read-write string register which contains the current
     output device (for example, `latin1' or `ps').  This is the only
     string register defined by `gtroff'.