equivalent date from GNU to solaris

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Tcl has a good free-form date scanner, if you have Tcl installed (try which tclsh). A shell function:

tcldate() {
    d=${1:-now}   # the date string
    f=${2:-%c}    # the output format
    echo "puts [clock format [clock scan {$d}] -format {$f}]" | tclsh
}

In action on an ancient Solaris 8 box with bash 2.03 and tcl 8.3.3

$ tcldate
Tue Jul 23 13:27:17 2013
$ i=4
$ tcldate "$i days"
Sat Jul 27 13:27:34 2013
$ tcldate "$i days" "%Y-%m-%d"
2013-07-27
$ tcldate "20130101 + $i days" "%Y-%m-%d"
2013-01-05

This even handles daylight savings transitions:

$ tcldate "2014-03-09 00:30 + 1 hour" "%D %T %Z"
03/09/14 01:30:00 EST
$ tcldate "2014-03-09 00:30 + 2 hour" "%D %T %Z"
03/09/14 03:30:00 EDT
$ tcldate "2013-11-03 00:30 + 1 hour" "%D %T %Z"
11/03/13 01:30:00 EDT
$ tcldate "2013-11-03 00:30 + 2 hour" "%D %T %Z"
11/03/13 01:30:00 EST

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