Hi,
I noticed that
date -d '5 days ago'
has as its counterpart
date -d '5 days'
if you want to know what day it will be 5 days hence. This is not
necessarily intuitive, and GNU date unfortunately doesn't have support for
the keyword "hence", meaning "from now".
The attached minor patch to lib/getdate.y fixes this, so that the symmetry
between "ago" and "hence" can be observed:
date -d '3 days ago'
date -d '3 days hence'
date -d '8 hours ago'
date -d '8 hours hence'
I'm also slightly concerned about the bit in lib/getdate.y's OtherTable
where "second" is commented out:
/* { "second", tUNUMBER, 2 }, */
I see that "second" as an ordinal specifier was removed because it
conflicts with "second" as a time unit. That leads to the unfortunate
behavior
[zork(~)] date -d 'first Wednesday'
Wed Dec 15 00:00:00 PST 1999
[zork(~)] date -d 'second Wednesday'
Wed Dec 15 00:00:01 PST 1999
[zork(~)] date -d 'third Wednesday'
Wed Dec 29 00:00:00 PST 1999
Obviously the result is that GNU date thinks of "second Wednesday" as
equivalent to "first second Wednesday":
[zork(~)] date -d 'first minute Wednesday'
Wed Dec 15 00:01:00 PST 1999
[zork(~)] date -d 'first hour Wednesday'
Wed Dec 15 01:00:00 PST 1999
[zork(~)] date -d 'ninth hour Wednesday'
Wed Dec 15 09:00:00 PST 1999
Is a consistent solution in which "second" can be either an ordinal or a
time unit without provoking serious confusion or resulting in serious
ambiguity?
I tell people to use "first Wednesday+1 week" instead of "second Wednesday",
but that may not be intuitive.
One last thing: what would it take to support something like
date -d 'November 1+fourth Wednesday'
in GNU date? (That syntax is accepted, but it gives a peculiar response.)
--
Seth Schoen, Senior Linux Consultant, Linuxcare, Inc.
415.354.4878 x326 tel, 415.701.7457 fax
[EMAIL PROTECTED], http://www.linuxcare.com/
Linuxcare. At the center of Linux.
--- lib/getdate.y.orig Sat Aug 7 02:39:05 1999
+++ lib/getdate.y Tue Dec 14 17:11:11 1999
@@ -184,7 +184,7 @@
enum _MERIDIAN Meridian;
}
-%token tAGO tDAY tDAY_UNIT tDAYZONE tDST tHOUR_UNIT tID
+%token tAGO tHENCE tDAY tDAY_UNIT tDAYZONE tDST tHOUR_UNIT tID
%token tMERIDIAN tMINUTE_UNIT tMONTH tMONTH_UNIT
%token tSEC_UNIT tSNUMBER tUNUMBER tYEAR_UNIT tZONE
@@ -347,6 +347,13 @@
| relunit
;
+rel : relunit tHENCE {
+ /* Nothing happens; default behavior for relative times.
+ Included for symmetry with tAGO. */
+ }
+ | relunit
+ ;
+
relunit : tUNUMBER tYEAR_UNIT {
yyRelYear += $1 * $2;
}
@@ -523,6 +530,7 @@
{ "eleventh", tUNUMBER, 11 },
{ "twelfth", tUNUMBER, 12 },
{ "ago", tAGO, 1 },
+ { "hence", tHENCE, 2 },
{ NULL, 0, 0 }
};
--- doc/getdate.texi.orig Wed Mar 25 05:40:21 1998
+++ doc/getdate.texi Tue Dec 14 18:14:28 1999
@@ -384,6 +384,7 @@
1 year ago
3 years
2 days
+3 weeks hence
@end example
@findex year @r{in date strings}
@@ -403,11 +404,14 @@
accepted and ignored.
@findex ago @r{in date strings}
+@findex hence @r{in date strings}
The unit of time may be preceded by a multiplier, given as an optionally
signed number. Unsigned numbers are taken as positively signed. No
number at all implies 1 for a multiplier. Following a relative item by
the string @samp{ago} is equivalent to preceding the unit by a
-multiplicator with value @math{-1}.
+multiplicator with value @math{-1}. Following a relative item by the
+string @samp{hence} has no effect, but may be useful to clarify that a
+relative time in the future is intended.
@findex day @r{in date strings}
@findex tomorrow @r{in date strings}
