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Re: I think bash logic in a loop like : while [ condition] |read somevar


From: Chris Down
Subject: Re: I think bash logic in a loop like : while [ condition] |read somevar is flawed.
Date: Tue, 24 Dec 2013 15:04:46 +0800
User-agent: Mutt/1.5.22 (2013-10-16)

On 2013-12-23 23:57:32 +0100, rens wrote:
> Hello,
> 
> this script:
> _______________________
> export cval=0
> echo entering while
> 
> # listing ten files, to generate some output to count.
> ls -1 /usr/bin|head -10 |while read fname

Just use a `for` loop and a glob. Really. It's that easy.

> do
> cval=$(( cval +1 ))
> echo cval = $cval  file = $fname
> done
> # one would think cval is now 10. but it is not, contrary to any other
> programming language........

Really, all other programming languages propagate variables from
children to parents? I find that hard to believe.

> that makes no sense.

Yes, it does. You created a subshell. How do you expect for the variable
to propagate back to the parent, where you are expanding it?

> Please Don't bother to tell me it s the way you guys think it should
> technically work.
> I know you think something along those lines, at least thats what I am
> told....

Don't use a subshell if you don't want one.

> However, no one in this world having to solve real life issues with
> software,  is interested in how it technically works. we need real life
> logic and software that can deal with real life challenges and requirements.

Then stop using a subshell.

> Bash  should not work that way. no programming language handles logic this
> way. Not pascal, korn shell, c shell, cobol, c, c++, lua , fortran or any
> other language i ever used.

None of the languages you listed propagate variables from children to
parents directly. I don't know why you think you should have that
variable in the parent when you populated it in a subshell...

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