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Full Discussion: if/elif help
Homework and Emergencies Homework & Coursework Questions if/elif help Post 302536489 by ygemici on Tuesday 5th of July 2011 01:56:56 PM
Old 07-05-2011
Quote:
Originally Posted by Morgan Greywolf
You guys are conflating two different POSIX shell mechanisms here. One is the arithmetic expansion and the other is command expansion. These are different.

$(()) denotes arithmetic expansion, and $() denotes command expansion.

Shells that support $() or $(()) generally support both. For older shells that do not support these syntaxes, you need to use backticks (`) for command expansion and arithmetic expansion isn't supported. In arithmetic expansion, Corona rightly reports that you do not need $ to expand variables; however, you do need this in command expansion. For example:
Code:
$ x=1
$ y=2
$ echo $((x+y))
3

However:
Code:
$ echo $(x+y)
x+y: command not found

OTOH, if we give it an expr command:
Code:
$ echo $(expr x + y)
expr: non-numeric argument

We need explicit variable expansion:
Code:
$ echo $(expr $x + $y)

BTW, if we want compatibility with older shells that do not support arithmetic expansion, we generally are not going to be able to use new-style command expansion, so we want something like this, instead:

Code:
$ echo `expr $x + $y`
3

we dont conflating anything.we are talking just arithmetic expansion about all shell variants.
I was referring to mentioned syntax of "$((x+y))" expression gives error on the some older shells..
In addition, I mentioned what i identified a issue that is maybe a bug in ash.
because of it(false statement) does not give any error at try of 3rd.

regards
ygemici
 

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NAME

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DESCRIPTION

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