bash: Arithmetic Expansion

1 
1 3.5.5 Arithmetic Expansion
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1 
1 Arithmetic expansion allows the evaluation of an arithmetic expression
1 and the substitution of the result.  The format for arithmetic expansion
1 is:
1 
1      $(( EXPRESSION ))
1 
1    The expression is treated as if it were within double quotes, but a
1 double quote inside the parentheses is not treated specially.  All
1 tokens in the expression undergo parameter and variable expansion,
1 command substitution, and quote removal.  The result is treated as the
1 arithmetic expression to be evaluated.  Arithmetic expansions may be
1 nested.
1 
1    The evaluation is performed according to the rules listed below
1 (⇒Shell Arithmetic).  If the expression is invalid, Bash prints a
1 message indicating failure to the standard error and no substitution
1 occurs.
1