10.3. Arithmetic

There is not really a need to do math problems in a shell script, but sometimes arithmetic is necessary, for instance, to increment or decrement a loop counter. The C shell supports integer arithmetic only. The @ symbol is used to assign the results of calculations to numeric variables.

10.3.1 Arithmetic Operators

The following operators shown in Table 10.1 are used to perform integer arithmetic operations. They are the same operators as found in the C programming language. See Table 10.6 on page 538 for operator precedence. Also borrowed from the C language are shortcut assignment operators, shown in Table 10.2.

Example 10.5.

1   % @ sum = 4 + 6

    echo $sum

    10

2   % @ sum++

    echo $sum

    11

3   % @ sum += 3

    echo $sum

    14

4   % @ sum--

    echo $sum

    13

5   % @ n = 3+4

    @: Badly formed number

Table 10.1. Integer Arithmetic Operators

Operator	Function
+	Addition
–	Subtraction
/	Division
*	Multiplication
%	Modulus
<<	Left shift
>>	Right shift

Table 10.6. Operator Precedence

Operator	Precedence	Meaning
( )	High Low	Change precedence; group
~		Complement
!		Logical NOT, negation
* / %		Multiply, divide, modulo
+ –		Add, subtract
<< >>		Bitwise left and right shift
> >= < <=		Relational operators: greater than, less than
== !=		Equality: equal to, not equal to
=~ !~		Pattern matching: matches, does not match
&		Bitwise AND
^		Bitwise exclusive OR
|		Bitwise inclusive OR
&&		Logical AND
||		Logical OR

Table 10.2. Shortcut Operators

Operator	Example	Equivalent To
+=	@ num += 2	@ num = $num + 2
–=	@ num –= 4	@ num = $num – 4
*=	@ num *= 3	@ num = $num * 3
/=	@ num /= 2	@ num = $num / 2
++	@ num++	@ num = $num + 1
––	@ num––	@ num = $num – 1

EXPLANATION