Operators in the shell

Basic arithmetic operations, as well as bitwise operations, can also be implemented in the shell.

We have summed up the following points:

1) Basic arithmetic operators: + 、-、 *,/, * * are supported, the last * * is a power operation;

2) arithmetic operations must be combined with some commands to use, such as expr ' ... ' Command, $ ((...)) Command, $[...] command, let command, note: Expr is followed by an anti-quote;

3) Be sure to note that there are spaces on both sides of the operator, such as result= ' expr 2 + 3 ' is correct, if it is result= ' expr 2+3 ' is wrong! The rest of the operators also need spaces separated!!

4) The parentheses operation in the arithmetic formula, multiplication operation must add the transfer character Slash, namely result= ' expr \ (2 + 3 \) \* 5 ' is correct, the division operation does not need;

5) expr can not be a power operation;

#-----------------------------/chapter4/ex4-28.sh------------------#! /bin/sh# calculates the difference between 2 and 100, that is, -98result= ' expr 2-100 ' echo ' $result ' #计算2和100的和, i.e. 102result= ' expr 2 + ' echo ' $result ' #计算2和5的乘积, That is, 10, multiplication sign must add the transfer character backslash result= ' expr 2 \* 5 ' echo "$result" #计算24和8的商, namely 3result= ' expr 24/8 ' echo ' $result ' #先计算2和6的差, and then multiplied by 12, i.e.-48 , brackets must be added with the transfer backslash result= ' expr \ (2-6 \) \* ' echo ' $result ' #错误的语法result = ' expr 2+5 ' echo ' $result #错误的语法result = ' expr 2-4*9 ' E Cho "$result" #错误的语法result = ' expr (4-7) ' echo ' $result '

6) Use $ ((...)) You can also do algorithmic book operations, and do not need to escape the operator and parentheses! There is no need to strictly specify the operator at both ends plus a space, the space can be added without adding. as follows:

#-----------------------------/chapter4/ex4-29.sh------------------#! /bin/sh# compact format, calculated for 3 and 6 and result=$ ((3+6)) echo "$result" #松散格式, calculates 3 and 9 and result=$ ((3 + 9)) echo "$result" #计算3和6的乘积reuslt =$ ((3 *  6) echo "$result" #计算7和5的商result =$ ((7/5)) echo "$result" #计算8和3的余数result =$ ((8 3)) echo "$result" #复合运算result =$ (((1-4 ) * 5) echo "$result"

So, use $ ((...)) form is more suitable for arithmetic operations.

7) use $[...] The form and above $ ((...)) The form of the same, more commonly used;

#-----------------------------/chapter4/ex4-30.sh------------------#! /bin/sh# addition Operation Result=$[4+5]echo "$result" #复合运算result =$[(1+2) *3]echo "$result" #幂运算result =$[2 * * 4]echo "$result"

8) Let can also implement arithmetic operations. Let is followed by a direct operation expression, the variable in the expression does not need to add $, direct use, as follows:

#-----------------------------/chapter4/ex4-31.sh------------------#! /bin/sh# Define Variable n=10# addition operation let N=n+1echo "$n" #乘法运算let N=n*10echo "$n" #幂运算let N=n**2echo "$n"

9) In addition to basic operations, the shell supports arithmetic characters: + =,-=, *=,/=,%=, and bitwise operators:<<, >>, &, |, ~, ^, <<=, >>=, &=, | =, ^=, and self-increment + +, self-reduction-operation;

Operators in the shell