How to obtain file date rather than current date

[dave at sq.UUCP]

In article <1986Oct8.182034.4245 at sq.uucp> dave at sq.UUCP I write:
>  The following troff macro, gR (GetReviseTime), assigns the latest
>  revision-date of the file in which it appears to the string whose name
>  is the argument in a call to gR:
>  
>  .de gR
>  .sy echo ".ds \\$1 `ls -l \n(.F | awk '{print $5, $6, $7}'`">/tmp/date\n($$
>  .so /tmp/date/\n($$
>  .sy rm /tmp/date\n($$
>  
>  After the above, in the file which is being formatted by ms, the
>  following:
>  
>  .gR dR
>  \*(dR
>  
>  would place the respective date in the output. It also works independent
>  of the ms macros.
>  
>  Note: the .sy request is available in DWB and ditroff.

Sorry folks. (Apologies in particular to beginners.)
The macro definition, above (gR), contains two typos:

	1. There should be a line ".." at the bottom, to end
	   the definition.
	2. An extra forward-slash appears in the ".so ..." line 
	   following the word "date".

The true definition is:

  .de gR
  .sy echo ".ds \\$1 `ls -l \n(.F | awk '{print $5, $6, $7}'`">/tmp/date\n($$
  .so /tmp/date\n($$
  .sy rm /tmp/date\n($$
  ..