Re: [groff] Changing A Defined String

[Tadziu Hoffmann]

If you want the following behavior:

  .ds DATE*FULL <modified date>
  The updated short date is \*[DATE*SHORT].

then I don't think that will be possible, since you can't do
any complex processing inside a string invocation.  If you
are willing to treat the dates as macros instead of strings,
like so:

  .DATE*FULL -set <modified date>
  The updated short date is
  .DATE*SHORT .

then you could do all sorts of stuff, including calling out
to the system for support.

If you must have the dates as strings, then I would adopt a
different model:

  .\" unsafe
  .\" ----------------------------------------------------------------
  .de GET_DATE
  .ds TEMP_FILE /tmp/groff.\n($$
  .sy date +'.ds DATE*DAY %-d%n.ds DATE*MONTH %-m%n.ds DATE*YEAR %Y%n.ds 
DATE*DAYNAME %A%n.ds DATE*DAYABBR %a%n.ds DATE*MONTHNAME %B%n.ds DATE*MONTHABBR 
%b' >\\*[TEMP_FILE]
  .so \\*[TEMP_FILE]
  .sy rm \\*[TEMP_FILE]
  ..
  .ds DATE*FULL \\*[DATE*DAYNAME], \\*[DATE*DAY] \\*[DATE*MONTHNAME] 
\\*[DATE*YEAR]
  .ds DATE*SHORT \\*[DATE*DAY] \\*[DATE*MONTHABBR] \\*[DATE*YEAR]
  .\" ----------------------------------------------------------------
  .GET_DATE
  .sp 3c
  Today is \m[red]\*[DATE*FULL]\m[] (or \m[red]\*[DATE*SHORT]\m[] for short).

and simply refrain from editing DATE*FULL, but only its
components DATE*DAY, DATE*MONTH, etc.  But I don't think
this will really be any better than getting into the habit
of always changing DATE*FULL and DATE*SHORT in lockstep.

Alternatively, you could write a macro SET_DATE, which sets
both DATE*FULL and DATE*SHORT, and you force yourself not to
overwrite DATE*FULL but to call the SET_DATE macro instead.