.TH gregorian "" "" "/rdb Command"
.PC "Convert column of dates for arithmetic and format change"
\fBgregorian  [ \-ceu ] [ \fIColumn ... \fB] < \fItableorlist\fR
.PP
.II "date^Gregorian"
.II "Gregorian date"
.II "date^convert"
The command
.B gregorian
converts Julian dates in one or more
.BR Column s
to Gregorian date.
When used with the command
.BR julian ,
you can do the following:
.IP \fB1.\fR 0.3i
Add days to a date.
.IP \fB2.\fR
Subtract days from a date.
.IP \fB3.\fR
Subtract two dates to find the number of days between them.
.IP \fB4.\fR
Change the format of a date.
.PP
A Gregorian date is a string that presents the date of the
current year, month, and day; for example ``911231''.
A Julian date, however, is the number of days since the
beginning of the Julian calendar (January 1, 4713 BC).
This system is used by astronomers, computer programmers, and other
people who wish to store dates in a form that can be
easily translated from one system of dating to another, without having
to worry about leap years, dates of the births of religious figures, etc.
Because Julian dates are integers,
you can subtract one from another to find the number of days between
two dates.
.PP
To perform arithmetic on dates, first use the command
.B julian
to convert the dates from Gregorian form to Julian.
Then, use the command
.B compute
to add or subtract the dates (or add a constant to a date).
Finally, use
.B gregorian
to convert the sum or the difference back to Gregorian form.
.SH Options
.B gregorian
recognizes the following options:
.IP \fB\-c\fR 0.3i
Output
\fIcomputer\fR
date format, i.e., \fIYYMMDD\fR.
.B /rdb
uses this format by default for its Gregorian dates
because it can be sorted and selected in correct numerical sequence.
.IP \fB\-e\fR
Output
.I European
date format, i.e., \fIDD/MM/YY\fR.
.IP \fB\-u\fR
Output
.I U.S.
date format, i.e., \fIMM/DD/YY\fR.
.SH Example
The first example shows how to add dates.
Suppose we have a file called
.BR journal ,
as follows:
.DM
Date    Account Debit   Credit  Description                       
------  ------- -----   ------  ----------------------------------
861222  101     25000           cash from loan
861222  211.1            25000  loan number #378-14 Bank Amerigold
861223  150.1   10000           test equipment from Zarkoff
861223  101               5000  cash payment
861223  211.2             5000  note payable to Zarkoff Equipment
861224  130     30000           inventory - parts from CCPSC
861224  201.1            15000  accounts payable to CCPSC
861224  101              15000  cash payment to CCPSC for parts
.DE
.PP
Now, suppose that we want to add 45 days to each of the dates.
First, see what
.B julian
does.
Typing
.DM
	julian Date < journal
.DE
.PP
prints the following on the standard output:
.DM
Date    Account Debit   Credit  Description                       
------  ------- -----   ------  ----------------------------------
1752827 101     25000           cash from loan
1752827 211.1            25000  loan number #378-14 Bank Amerigold
1752828 150.1   10000           test equipment from Zarkoff
1752828 101               5000  cash payment
1752828 211.2             5000  note payable to Zarkoff Equipment
1752829 130     30000           inventory - parts from CCPSC
1752829 201.1            15000  accounts payable to CCPSC
1752829 101              15000  cash payment to CCPSC for parts
.DE
.PP
The
.B Date
column now holds a Julian date.
Note we gave no option because computer format is the default.
.PP
The next command adds 45 days to each entry in the
.B Date
column:
.DM
julian Date < journal | compute 'Date += 45' | gregorian Date
.DE
.PP
This command prints the following on the standard output:
.DM
Date    Account Debit   Credit  Description                       
------  ------- -----   ------  ----------------------------------
870205  101     25000           cash from loan
870205  211.1            25000  loan number #378-14 Bank Amerigold
870206  150.1   10000           test equipment from Zarkoff
870206  101               5000  cash payment
870206  211.2             5000  note payable to Zarkoff Equipment
870207  130     30000           inventory - parts from CCPSC
870207  201.1            15000  accounts payable to CCPSC
870207  101              15000  cash payment to CCPSC for parts
.DE
.PP
As you can see, every date is now 45 days later than they originally were.
.PP
The next example converts one format of Gregorian date to another.
To convert the
.B Date
column in our example table from computer format to U.S. format,
type the following:
.DM
	julian Date < journal | gregorian -u Date | justify Date
.DE
.PP
The result is as follows:
.DM
Date            Account Debit   Credit  Description                       
--------        ------- -----   ------  ----------------------------------
12/22/86        101     25000           cash from loan
12/22/86        211.1            25000  loan number #378-14 Bank Amerigold
12/23/86        150.1   10000           test equipment from Zarkoff
12/23/86        101               5000  cash payment
12/23/86        211.2             5000  note payable`to Zarkoff Equipment
12/24/86        130     30000           inventory - parts from CCPSC
12/24/86        201.1            15000  accounts payable to CCPSC
12/24/86        101              15000  cash payment to CCPSC for parts
.DE
.PP
Because the U.S. format is two characters wider than the
computer format, we included the command
.B justify
in our command line to line things up.
.SH "See Also"
.B
compute,
computedate,
julian
.R
.br
COHERENT Lexicon:
.B
awk,
date
.R