Rdb: Ruby-Nachbau der MWC /rdb-Werkzeuge

man/computedate.man

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+.TH computedate "" "" "/rdb Command"
+.PC "Add given number of days to a date"
+\fBcomputedate \fIdate  days\fR
+.PP
+.II "date^arithmetic"
+.II "arithmetic^date"
+The command
+.B computedate
+adds days to a date, and displays the new date.
+.I date
+must be the format \fIYYMMDD\fR;
+.I days
+can be negative or positive.
+.B computedate
+displays the new date in the same format.
+This is the best format for entering dates in a column
+because they sort correctly and take only six characters.
+.PP
+Internally,
+.B computedate
+converts the date to
+.BR julian ,
+adds days, then converts the date back to
+.BR gregorian .
+Suppose we want to know the date 45 days from March 31, 1989.
+We can type:
+.DM
+	computedate 890331 45
+.DE
+.PP
+This command returns the string:
+.DM
+	890515
+.DE
+.PP
+That is May 15, 1989.
+.PP
+Another trick is to combine the
+.B todaysdate
+and the
+.B computedate
+programs.
+.B todaysdate
+gives the date of today in the preferred format of \fIYYMMDD\fR.
+For example, the following command shows us the date 45 days from today:
+.DM
+	computedate `todaysdate` 45
+.DE
+.SH "Data Validation"
+You can use
+.B computedate
+to validate a date.
+If you add zero days to a date and get a different date, then
+the original date was not valid.
+For example, let's test the 32nd day of January 1989:
+.DM
+	computedate 890132 0
+.DE
+.PP
+This returns the string
+.B 890201
+or February 1, 1989.
+As we expected, we received a different date.
+We can test this with the following shell program:
+.DM
+	if test $DATE = `computedate $DATE 0`
+	then
+		echo OK
+	else
+		echo Invalid DATE
+	fi
+.DE
+.SH "See Also"
+.B
+gregorian,
+julian,
+todaysdate
+.R