Re: days difference between two dates
From: Alan Connor (xxxxxx_at_xxxx.xxx)
Date: 08/25/03
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Date: Mon, 25 Aug 2003 16:41:40 GMT
On Mon, 25 Aug 2003 16:51:41 +0200, Heiner Steven <heiner.steven@nexgo.de> wrote:
>
>
> Edgar Allen wrote:
>
> > <html><input type crash></html>
> > begin joe@invalid.address wrote:
> >
> >>If you come up with a link to ADU that works, please let me know and
> >>I'll add it to the FAQ.
> >
> > Does the FAQ include ?
> >
> > Linkname: mktime - A command to manipulate time and date values
> > URL: http://members.rogers.com/weirdways/technogeek/source/mktime/
>
> I think the answers our FAQ gives and the examples it provides
> should try to be
>
> (1) shell only
> one big advantage of shell scripts are that they run on
> different platforms without need for compilation. This is
> even more important in the light of Unices that
> don't even have a C compiler as part of the standard
> distribution, e.g. Sun's Solaris (what about AIX, HP-UX?)
>
> (2a) self contained
> Solutions should not depend on other tools that need to
> be installed separately. "awk", "sed", "expr" are examples
> of tools that can be assumed to be installed, but a C compiler,
> "python", or the program "netcat" cannot be.
>
> (2b) use POSIX conformant tools
> The answers examples should not depend on non-portable,
> non-standard functionality. For example, "find ... -print0"
> is very useful, but it's a GNU extension that is not available
> on e.g. Solaris (and probably AIX, HP-UX, too). In case of
> doubt, the POSIX solution should be listed first, and then
> other (e.g. GNU-specific) ones.
>
> (3) as portable as possible
> Bourne shell solutions should be listed prior to
> KornShell-specific ones.
>
> The portable
>
> base=`basename "$0"`
>
> should be listed in additon to a KornShell/BASH solution
> like
>
> base=${0##*/}
>
> Although the latter example may be faster (and more elegant
> in the eyes of some people), the former solution is much
> more portable.
>
> (4) easily readable, even if not 100% correct
> Sometimes scripts are easy to write, but it's hard to
> make them 100% correct (e.g. handle new-lines in file names
> or backslashes '\' in the input).
> Since the FAQ is addressed to shell scripting beginners,
> it's of paramount importance that the examples are easy to
> understand. Therefore, a script example that works in
> 95% of the cases and that is easy to read and understand should
> be preferred to a script that is 100% correct but that is hard
> to understand.
> I don't say we should not give the 100% correct solution,
> just that we present an easy, 90% solution, too.
>
> We cannot expect the readers of the FAQ to understand a
> script line that we fine-tuned for years for correctness.
> Give them a chance to find out how easily the shell
> can be used to automate tasks. Don't confuse them with
> perfect solutions they cannot understand, and therefore
> cannot learn from.
>
> IMHO perfect solutions should be part of some shell
> script library archive (e.g. something comparable to
> Perl's CPAN).
>
> Regarding the "mktime" program: this program is useful
> and maybe deserves a link in the FAQ, but IMHO should
> not be listed as the "standard" solution to date arithmetic.
>
> Heiner
I'm with you, Heiner.
That "shell script library" sounds like a wonderful idea.
Now, if I could only get a copy of that FAQ ......
Alan C
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