1 #!/bin/bash
 2 #算术运算符实例
 3 a=10
 4 b=20
 5 
 6 val=`expr $a + $b`
 7 echo "a + b : $val"  #30
 8 
 9 val=`expr $a - $b`
10 echo "a - b : $val" #-10
11 
12 val=`expr $a \* $b` #不加转义符号（\）会报错：expr: syntax error
13 echo "a * b : $val" #200
14 
15 val=`expr $a / $b`
16 echo "b / a : $val" #0
17 
18 val=`expr $a % $b`
19 echo "b % a : $val" #10
20 
21 
22 if [ $a == $b ]
23 then
24 echo "a等于b"
25 fi
26 
27 if [ $a != $b ] #b与]之间不加空格时会报错：./test.sh: line 27: [: missing `]'
28 then 
29 echo "a不等于b"
30 fi