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

1. The variable sum is assigned the result of adding 4 and 6 . (The space after the @ is required.)

2. The variable sum is incremented by 1 .

3. The variable sum is incremented by 3 .

4. The variable sum is decremented by 1 .

5. Space