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Arithmetic Evaluation

The shell allows arithmetic expressions to be evaluated, as one of the shell expansions or by the let builtin.

Evaluation is done in long integers with no check for overflow, though division by 0 is trapped and flagged as an error. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence.

- +

unary minus and plus

! ~

logical and bitwise negation

* / %

multiplication, division, remainder

+ -

addition, subtraction

<< >>

left and right bitwise shifts

<= >= < >

comparison

== !=

equality and inequality

&

bitwise AND

^

bitwise exclusive OR

|

bitwise OR

&&

logical AND

||

logical OR

= *= /= %= += -= <<= >>= &= ^= |=

assignment

Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. The value of a parameter is coerced to a long integer within an expression. A shell variable need not have its integer attribute turned on to be used in an expression.

Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take the form [base#]n, where base is a decimal number between 2 and 36 representing the arithmetic base, and n is a number in that base. If base is omitted, then base 10 is used.

Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above.

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