I agree with shamrock, and there is a perl version of date right here: General Purpose Date Script -- I call it date.pl on my system.
Here's a demo snippet:
pl " Standard date:"
/usr/bin/date
pl " Standard date with arithmetic correction of -15 hours (expect fail):"
/usr/bin/date --date="15 hours ago"
pl " Standard date with arithmetic correction of -15 hours (expect fail):"
/usr/xpg4/bin/date --date="15 hours ago"
pl " perl version of date:"
date.pl --date="-15 hours"
producing:
Standard date:
Sun Apr 10 03:25:53 CDT 2016
-----
Standard date with arithmetic correction of -15 hours (expect fail):
/usr/bin/date: illegal option -- date=15 hours ago
usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]
-----
Standard date with arithmetic correction of -15 hours (expect fail):
/usr/xpg4/bin/date: illegal option -- date=15 hours ago
usage: date [-u] mmddHHMM[[cc]yy][.SS]
date [-u] [+format]
date -a [-]sss[.fff]
-----
perl version of date:
2016-04-09 12:25:54
For a sysem like:
Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: SunOS, 5.11, i86pc
Distribution : Oracle Solaris 11.3 X86
bash GNU bash 4.1.17
date - ( /usr/bin/date, 2016-04-10 )
date.pl - ( local: RepRev 1.4, ~/bin/date.pl, 2014-02-18 )