Re: Command-line-interface (CLI) calculator to work out the difference between 2 dates

[Ron Johnson <ron.l.johnson@cox.net>]

On 08/24/08 11:32, Rick Pasotto wrote:
> On Sun, Aug 24, 2008 at 11:25:31AM -0500, Ron Johnson wrote:
> > On 08/24/08 10:54, Edward J. Shornock wrote:
> > [snip]
> > > While I'm sure someone else will provide a much better way, I've used  
> > > something like
> > >
> > > $ echo $(date  -d 20080824 +%j) - $(date  -d 20080724 +%j) | bc
> > > 31
> > That a good idea.  I never knew date(1) could do that.  The problem,  
> > though, is that it doesn't span years.
> >
> > $ echo $(date -d 20090824 +%j) - $(date -d 20080724 +%j) | bc
> > 30
> >
> > Use delta from epoch, instead.
> > $ echo $[$(date -d 20090824 +%s) - $(date -d 20080724 +%s)]/86400|bc
> > 396
>
> Why pipe it to bc? Keep it in the shell:
>
> $ echo $[$[$(date -d 20090824 +%s) - $(date -d 20080724 +%s)] / 86400]
> 396

I was thinking that integer division might result in the occasional 
rounding error.  But now that I think about it, that wouldn't 
matter, since bc does integer math unless you pass it "-l".

One stylistic reason for piping to bc is that some people think that 
bash's $[] syntax gets too hard to read if you nest it too much.

--
Ron Johnson, Jr.
Jefferson LA  USA

"Do not bite at the bait of pleasure till you know there is no
hook beneath it."  -- Thomas Jefferson