Re: hour -1 routine

From: Wiggins D Anconia (wiggins_at_danconia.org)
Date: 05/28/04 

Date: Fri, 28 May 2004 11:02:35 -0600
To: "Anthony J Segelhorst" <ajs15@meadwestvaco.com>, beginners@perl.org

>
> "Wiggins d Anconia" <wiggins@danconia.org> wrote on 05/28/2004 12:37:56
> PM:
>
> > >
> > > I am trying to set up a script that will do the do a current time -1
> > > routine.
> > >
> > > Examples:
> > >
> > > Current Time:
> > > mmddyy:hhss
> > > 052804:1030
> > >
> > > Output:
> > > 052804:0930
> > >
> > >
> > > Current Time:
> > > 052704:0015
> > >
> > > Output:
> > > 052604:23:15
> > >
> > >
> > > I think the add_delta module is where I need to go, but I have never
> used
> > > modules before.
> > >
> >
> > add_delta is probably a method/function in Date::Calc or Date::Manip
> > modules. But in this case is probably overkill.
> >
> > You can use the built-in functions 'time' and 'localtime' to get the
> > desired effect.
> >
> > perldoc -f time
> > perldoc -f localtime
> >
> > 'time' will return the current time, from which you can subtract 60*60
> > (60 seconds in each of 60 minutes), which gives 1 hour ago. You can then
> > use localtime to retrieve the values for the specific fields you need at
> > the calculated time. Alternatively you could use POSIX::strftime for
> > the formatting.
> >
> > perldoc POSIX
> >
> > HTH,
> >
> > http://danconia.org
>
> If I understand what you are saying about subtract 60 seconds in each of
> 60 minutes, how will this be able to handle:
>
> 1. When it is 00:15, because if it is 00:15 I will actually want
> 23:15
> 2. I can not just subtract 1 from the date because 010104 needs
> to really be 123104.
>
> If this is not what you are suggesting, let me know. You might be onto
> something.
>
>
> This is the part that is confusing me currently. I am just trying to get
> logical understanding of what I want to do before I start writing the
> code.
>

Excellent questions. 'time' returns the number of seconds from a
specific point in time, in most cases Jan 1 1970, 00:00:00. So for
instance when I started this sentence, I had the following # of seconds:

1085762425

>From this I can subtract 60*60 to get 1 hour ago from the point when the
time was read as it relates to that initial starting point (also known
as the epoch, Jan 1 1970).

Then using 'localtime' I can translate that time back into a readable
format. Because localtime is just translating a set point in time, and
all of my calculations were done using seconds, I don't have to worry
about boundaries, such as hour, day, month, or years.

There are a lot of caveats about working with times, but the same is
going to hold whether you are using something like 'add_delta' or the
built-ins.

Make sense? I am reluctant to just give code since it doesn't
reinforce the learning, but if you are still stuck post again, we will
get you sorted.

http://danconia.org

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