06-09-2008
Problem number 1 is you're mixing date math with integer math. You cannot add 1 to your "0530" and expect to get the next day. For example, there is no integer "0530". There is an integer "530", however, and if you add 1 to it you will get "531". ...NOT the "0531" that you need. And, as you mentioned, adding 1 to that will not get you into June.
The problem of shell date arithmetic is fairly difficult. See
"Date math in Linux shell script?": Tech Support from Ask Dave Taylor! .
When you do your comparison, you can test for your end condition in either of two ways:
- If the current date == the end date (string comparison)
- If the current iterations number of seconds since the epoch is less than or equal to the end date's number of seconds since the epoch.
Also, here's a couple of more gotchas you need to be aware of. If you do your date math using "number of seconds since the Epoch",
- You may want your first date to actually be midnight of the first date- that is, the 0'th second of that day.
- You may want your second date to actually be 23:59:59 on that day.
This is because if you do your "begin <= end" comparison, you may be comparing 3pm on the end day to 2pm on the end day and that iteration of the script will not run.
I mention that because it's convenient to actually do the date math by:
- Convert the first date to the number of seconds since the epoch
- Increment the date by adding 86,400 (the number of seconds in a day) to the date for each iteration.
You also must be aware of when the year changes. Don't forget you may be comparing dates in January to dates in December.
-mschwage
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DATE(1) General Commands Manual DATE(1)
NAME
date - print or set the date and time
SYNOPSIS
date [-qsu] [[MMDDYY]hhmm[ss]] [+format]
OPTIONS
-q Read the date from stdin
-s Set the time (implicit for -q or a date string)
-u Print the date as GMT
-t Use this number of seconds instead of current time
EXAMPLES
date # Print the date and time
date 0221921610 # Set date to Feb 21, 1992 at 4:10 p.m.
DESCRIPTION
With the -q flag or a numeric argument, date sets the GMT time and date. MMDDYY refers to the month, day, and year; hhmmss refers to the
hour, minute and second. Each of the six fields must be exactly two digits, no more and no less. date always display the date and time,
with the default format for the system. The -u flag request GMT time instead of local time. A format may be specified with a + followed
by a printf-like string with the following options:
%% % character
%A Name of the day
%B Name of the month
%D mm/dd/yy
%H Decimal hour on 2 digits
%I Decimal hour modulo 12 on 2 digits
%M Decimal minute on 2 digits
%S Decimal seconds on 2 digits
%T HH:MM:SS
%U Decimal week number, Sunday being first day of week
%W Decimal week number, Monday being first day of week
%X Same as %T
%Y Decimal year on 4 digits
%Z Time Zone (if any)
%a Abbreviated name of the day
%b Abbreviated name of the month
%c Appropriate date & time (default format)
%d Decimal day of the month on 2 digits
%e Same as %d, but a space replaces leading 0
%h Same as %b
%j Decimal dey of the year on 3 digits
%m Decimal month on 2 digits
%n Newline character
%p AM or PM
%r 12-hour clock time with AM/PM
%s Number of seconds since the epoch
%t Tab character
%w Decimal day of the week (0=Sunday)
%x Same as %D
%y Decimal year on 2 digits
SEE ALSO
time(2), ctime(3), readclock(8).
DATE(1)