*arith* *arithmetic* *arithmetic-expansion*

#ARITHMETIC EXPANSION#

Arithmetic expansion evaluates a mathematical expression and substitutes
the result. The expression is subject to parameter expansion and command
substitution before evaluation.

  `$((expression))`

      Example:
        `echo $((2 + 3))`       # prints: 5
        `x=$((width * height))`

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1. Operators                                   *arith-operators*

  The following operators are supported, listed from highest to lowest
  precedence:

  `( )`                                        *arith-parens*

      Grouping. Override default precedence.

      Example:
        `echo $(( (2+3) * 4 ))`  # prints: 20

  `*` `/` `%`                                  *arith-muldivmod*

      Multiplication, division, and modulo (remainder).

      Example:
        `echo $((10 / 3))`       # prints: 3
        `echo $((10 % 3))`       # prints: 1

  `+` `-`                                      *arith-addsub*

      Addition and subtraction.

      Example:
        `echo $((10 - 3 + 1))`   # prints: 8

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2. Variables in Expressions                    *arith-variables*

  Variables can be referenced by name inside arithmetic expressions.
  They are expanded and converted to numbers.

      `x=10`
      `echo $(($x + 5))`        # prints: 15
      `echo $((x + 5))`         # also works

  If a variable is unset or not a valid number, an error is reported.

==============================================================================
3. Nesting                                     *arith-nesting*

  Arithmetic expressions can be nested with parentheses to any depth:

      `echo $(( (1+2) * (3+4) ))`  # prints: 21

  Arithmetic expansion can also appear inside other expansions:

      `echo "Total: $((price * qty))"`

==============================================================================
4. Whitespace                                  *arith-whitespace*

  Whitespace inside `$((...))` is ignored and can be used freely for
  readability:

      `echo $((2+3))`           # prints: 5
      `echo $(( 2 + 3 ))`       # same result

==============================================================================
See also: |param| |redirect| |glob|