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From: Ed Morton on 7 Feb 2010 14:12
On 2/7/2010 11:26 AM, Seebs wrote:
> On 2010-02-07, Ed Morton<mortonspam(a)gmail.com> wrote:
>> Writing a shell loop is something you
>> should do after you've thought about whether or not it's really the best
>> approach as it usually isn't
>
> Define "usually". The circumstances in which I find myself writing loops
> in shell scripts are usually cases where I want to perform a series of
> operations on each of several files, and while existing tools can often
> perform a single operation on several files, trying to do them in a pipeline
> seems doomed to failure.
>
> -s

"usually" means "almost always unless you're creating/moving/removing multiple
files and/or operating on multiple processes".

Ed.
From: Seebs on 7 Feb 2010 14:27
On 2010-02-07, Ed Morton <mortonspam(a)gmail.com> wrote:
> On 2/7/2010 11:26 AM, Seebs wrote:
>> On 2010-02-07, Ed Morton<mortonspam(a)gmail.com> wrote:
>>> Writing a shell loop is something you
>>> should do after you've thought about whether or not it's really the best
>>> approach as it usually isn't

>> Define "usually". The circumstances in which I find myself writing loops
>> in shell scripts are usually cases where I want to perform a series of
>> operations on each of several files, and while existing tools can often
>> perform a single operation on several files, trying to do them in a pipeline
>> seems doomed to failure.

> "usually" means "almost always unless you're creating/moving/removing
> multiple files and/or operating on multiple processes".

Ahh. See, since those are the circumstances in which I'm most likely to
think to write a loop in a shell program, it turns out that, of cases in
which I am thinking of writing a loop in shell, most often it is a good
fit.

The one exception I've had recently is that I wanted to generate some
number sequences and, for various reasons, could not safely rely on the
existence of any of the usual (jot, seq) candidates, so I did them as
one-liner shell loops.

-s
--
Copyright 2010, all wrongs reversed. Peter Seebach / usenet-nospam(a)seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
From: Chris F.A. Johnson on 8 Feb 2010 07:11
On 2010-02-07, Ed Morton wrote:
> On 2/7/2010 11:26 AM, Seebs wrote:
>> On 2010-02-07, Ed Morton<mortonspam(a)gmail.com> wrote:
>>> Writing a shell loop is something you
>>> should do after you've thought about whether or not it's really the best
>>> approach as it usually isn't
>>
>> Define "usually". The circumstances in which I find myself writing loops
>> in shell scripts are usually cases where I want to perform a series of
>> operations on each of several files, and while existing tools can often
>> perform a single operation on several files, trying to do them in a pipeline
>> seems doomed to failure.
>>
>> -s
>
> "usually" means "almost always unless you're creating/moving/removing multiple
> files and/or operating on multiple processes".

I would interpret it to mean "unless you are operating on a [large] file".

--
Chris F.A. Johnson, author <http://shell.cfajohnson.com/>
===================================================================
Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)
===== My code in this post, if any, assumes the POSIX locale =====
===== and is released under the GNU General Public Licence =====
From: Ed Morton on 8 Feb 2010 11:12
On Feb 6, 10:48 pm, Kaz Kylheku <kkylh...(a)gmail.com> wrote:
> On 2010-02-07, Ed Morton <mortons...(a)gmail.com> wrote:
>
> > Note that in general if you find yourself writing a loop in a shell script, it's
> > the wrong approach.
>
> On one recent project, I wrote not only a loop in a shell script, but in
> fact a loop which reads input from a file, lexically analyzes, parses it
> and interprets another language; a domain-specific language for
> constructing a file system image with customized contents.

Then that almost certainly took you longer to write and resulted in a
less efficient, more error-prone, more complicated, and less
extensible script than if you'd taken a different approach.

Ed.
From: David Combs on 21 Feb 2010 20:11
In article <hkl7sf$ipv$1(a)news.eternal-september.org>,
Ed Morton <mortonspam(a)gmail.com> wrote:
....
....

>printf "Enter the number of values to be input: "; read numv;
>
>while (( counter < numv ))
^ -----^---- The extra paren-pair "hides" the "<"
from being interpreted as a redirection? (Looks like it would.)

Not that I know bash ("let"?) -- as bool, does "<" work
on numbers, or must he use ".lt."?

Silly questions -- maybe those "lets" gave me a concussion!


David


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