Shell 实现简单计算器功能

[root@nfs scripts]# cat jisuan.sh
#!/bin/bash
print_usage(){
printf $"USAGE:$0 NUM1 {+|-|*|/} NUM2\n"
exit 1
}

#判断传入的参数是不是3个
if [ $# -ne 3 ]
then
print_usage
fi

firstnum=$1
secondnum=$3
op=$2

#对传入的参数进行判断看是不是合理
if [ -n "`echo $firstnum|sed 's/[0-9]//g'`" ];then
print_usage
fi

if [ "$op" != "+" ]&&[ "$op" != "-" ]&&[ "$op" != "*" ]&&[ "$op" != "/" ];then
print_usage
fi

if [ -n "`echo $secondnum|sed 's/[0-9]//g'`" ];then
print_usage
fi

echo "${firstnum}${op}${secondnum}=$((${firstnum}${op}${secondnum}))"

[root@nfs scripts]# sh -x jisuan.sh 6 + 4
+ '[' 3 -ne 3 ']'
+ firstnum=6
+ secondnum=4
+ op=+
++ sed 's/[0-9]//g'
++ echo 6
+ '[' -n '' ']'
+ '[' + '!=' + ']'
++ sed 's/[0-9]//g'
++ echo 4
+ '[' -n '' ']'
+ echo 6+4=10
6+4=10
[root@nfs scripts]# sh -x jisuan.sh 5 \* 5
+ '[' 3 -ne 3 ']'
+ firstnum=5
+ secondnum=5
+ op='*'
++ sed 's/[0-9]//g'
++ echo 5
+ '[' -n '' ']'
+ '[' '*' '!=' + ']'
+ '[' '*' '!=' - ']'
+ '[' '*' '!=' '*' ']'
++ sed 's/[0-9]//g'
++ echo 5
+ '[' -n '' ']'
+ echo '5*5=25'
5*5=25