Am 02. Mär, 2015 schwätzte Michael Havens so:

moin moin Mike,

see the Arithmetic Expansion portion of the bash man page for details.

$((expression))

That says to evaluate the expression and substitute the result. Remember
that the shell only does interger math, no decimals.

:) ~$ echo $(( 4 / 2 ))
2
:) ~$ echo $(( 4 / 3 ))
1
:) ~$ echo $(( 4 * 3 ))
12
:) ~$

Note that you don't need to escape the * when using arithmetic expansion
because the $(( )) is already quoting.

ciao,

der.hans

> just starting with this so please, bear with me....
>
> Anyways I am looking at this beginner's script:
>
>   #! /bin/bash
>   myvar=0
>   while [ $myvar -ne 20 ]
>   do
>           echo $myvar
>           myvar=$(( $myvar + 1 ))
>   done
>
> Now my mind can wrap itself around everything in this script except for tis
> line:
>
>   myvar=$(( $myvar + 1 ))
>
> Where my difficulty arises is why the '$' before the '(('?
> (it was geast fun running that script with a minus sign instead!)
> :-)~MIKE~(-:
>

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