前一段时间受人之托，说是毕业设计非要用shell写个计算器，要支持四则运算的，刚开始觉得还容易，可发现四则的匹配还是比较繁琐的，在这里分享下吧～估计之后也不会出这样的毕业设计了

PS：赶时间写的，有bug的欢迎指正

1. #!/bin/bash 
2.  
3. ## Calculator.sh ## 
4. main() 
5. { 
6.     echo 'This is a Calculator:' 
7.     echo 'example: 3 + 90 x ( 9 - 5 ) / 3 - 23'  
8.     call 
9. } 
10.  
11.  
12. call() 
13. { 
14.     while [ 1 ];do 
15.         read str 
16.                 u=($str) 
17.         g1='no' 
18.         g2='no' 
19.                 nu=`echo $str | awk '{print NF}'` 
20.         for((i=0;i<$nu;i++));do 
21.             echo ${u[$i]} | grep -E '^[1-9]|+|-|x|/|\(|\)' > /dev/null 
22.             if (( $? == 0 ));then 
23.                 echo ${u[$i]} |grep -E '\(|\)' > /dev/null 
24.                                         if (( $? == 0 ));then 
25.                                                 echo ${u[$i]} |grep -w '(' > /dev/null 
26.                                                 if (( $? == 0 ));then 
27.                             g1=$i 
28.                             continue 
29.                         fi 
30.  
31.                                                 echo ${u[$i]} |grep -w ')' > /dev/null 
32.                                                 if (( $? == 0 ));then 
33.                                                         g2=$i 
34.                             if [ $g1 != 'no' ] || [ $g2 != 'no' ];then 
35.                                             compute $g1 $g2 
36.                                 u[$g1]=$? 
37.                                 for((p=$g1+1;p<$g2+1;p++));do 
38.                                     u[$p]='' 
39.                                 done                                 
40. #                               echo ${u[@]} 
41.                                 nu3=`echo ${u[@]} | awk '{print NF}'` 
42.                                 compute 0 $nu3 
43.                                 echo $?  
44.                                     fi 
45.                             continue 
46.                         fi 
47.                     fi 
48.                         else 
49.                                 echo 'Error: is not digital' 
50.             fi 
51.         done 
52.  
53.         if [ $g1 = 'no' ] || [ $g2 = 'no' ];then 
54.             compute 0 $nu 
55.             echo $? 
56.         fi 
57.     done 
58. } 
59.  
60. compute() 
61. { 
62.     s=(${u[@]}) 
63.     for((k=$1;k<$2;k++));do 
64.  
65.         echo ${s[$k]} |grep -E 'x|/' > /dev/null 
66.             if (( $? == 0 ));then 
67.                 echo ${s[$k]} |grep -w 'x' > /dev/null 
68.                 if (( $? == 0 ));then 
69.                     sum=`expr ${s[$k-1]} \* ${s[$k+1]}` 
70.                     s[$k+1]=$sum 
71.                     s[$k]='' 
72.                     s[$k-1]='' 
73.                     continue 
74.                 fi 
75.  
76.                                 echo ${s[$k]} |grep -w '/' > /dev/null 
77.                                 if (( $? == 0 ));then 
78.                                         sum=`expr ${s[$k-1]} \/ ${s[$k+1]}` 
79.                     s[$k+1]=$sum 
80.                                         s[$k]='' 
81.                                         s[$k-1]='' 
82.                                         continue 
83.  
84.                                  fi 
85.             fi 
86.         echo ${s[@]} |grep -E '+|-' > /dev/null 
87.             if (( $? == 0 ));then 
88.                 t=(${s[@]}) 
89.                 nu2=`echo ${t[@]} | awk '{print NF}'` 
90.                 for((j=$1;j<$2;j++));do 
91.                         echo ${t[$j]} |grep -E '+|-' > /dev/null 
92.                                 if (( $? == 0 ));then 
93.                                     echo ${t[$j]} |grep -w '+' > /dev/null 
94.                                         if (( $? == 0 ));then 
95.                                             sum=`expr ${t[$j-1]} + ${t[$j+1]}` 
96.                                                 t[$j+1]=$sum 
97.                             t[$j]='' 
98.                             t[$j-1]='' 
99.                                                     continue 
100.                                             fi 
101.  
102.                                             echo ${t[$j]} |grep -w '-' > /dev/null 
103.                                             if (( $? == 0 ));then 
104.                                                 sum=`expr ${t[$j-1]} - ${t[$j+1]}` 
105.                                                     t[$j+1]=$sum 
106.                                                     t[$j]='' 
107.                                                     t[$j-1]='' 
108.                                                     continue 
109.                                             fi       
110.                          
111.                     fi 
112.                 done 
113.             fi 
114.     done 
115.     return $sum 
116. } 

运行结果：

1. zhangbo@ufo:~/me/shell$ ./Calculator.sh  
2. This is a Calculator: 
3. example: 3 + 90 x ( 9 - 5 ) / 3 - 23 
4. 3 + 90 x ( 9 - 5 ) / 3 - 23        
5. 100 
6. 2 x ( 3 + 10 ) 
7. 26