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$((...)) and $[...] comparison


 
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# 1  
Old 12-21-2009
$((...)) and $[...] comparison

Does $((mathematical expression)) and $[mathematical expression] mean the same?

Last edited by proactiveaditya; 12-21-2009 at 04:18 PM..
# 2  
Old 12-21-2009
What does '$[mathematical expression]' do exactly?
# 3  
Old 12-21-2009
Code:
[root@pn]# a=3
[root@pn]# b=2
[root@pn]# echo $[a-b]
1
[root@pn]# echo $((a-b))
1

Are they equivalent with regards to Arithmetic evaluation?
# 4  
Old 12-21-2009
They are equivalent in bash but according to the man pages:
Quote:
The old format $[expression] is deprecated and will be removed in upcoming versions of bash
# 5  
Old 12-21-2009
It's the first time I see this ...

Quote:
$[ expression ]
Code:
$ bash -c 'echo  $[ 2 + 3 ]'
5
$ zsh -c 'echo  $[ 2 + 3 ]'
5
$ ksh93 -c 'echo  $[ 2 + 3 ]'
$[ 2 + 3 ]
$ pdksh -c 'echo  $[ 2 + 3 ]'
$[ 2 + 3 ]



---------- Post updated at 09:57 PM ---------- Previous update was at 09:56 PM ----------

Quote:
Originally Posted by Scrutinizer
They are equivalent in bash but according to the man pages:
What version of bash are you using?
# 6  
Old 12-21-2009
Quote:
Originally Posted by radoulov

What version of bash are you using?
3.2.39
# 7  
Old 12-21-2009
Quote:
Originally Posted by Scrutinizer
3.2.39
Thank you, I cannot find this in the man pages of the bash version I'm currently using, but I found it in the zsh manual pages:

Quote:
ARITHMETIC EXPANSION
A string of the form `$[exp]' or `$((exp))' is substituted with the value of the arithmetic
expression exp. exp is subjected to parameter expansion, command substitution and arith-
metic expansion before it is evaluated.

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