Shell Implements simple calculator function

The Shell implements a simple calculator function with the following script:

[[email protected] scripts]# Cat Jisuan.sh#!/bin/bashprint_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_usagefifirstnum=$1secondnum=$3op=$2# to determine the incoming parameters to see if it is reasonable if [-n "' Echo $firstnum |s Ed ' s/[0-9]//g ' "];then print_usagefiif [" $op "! =" + "]&&[" $op "! ="-"]&&[" $op "! =" * "]&& ["$op"! = "/"];then Print_usagefiif [-N "' Echo $secondnum |sed ' s/[0-9]//g '"];then Print_usagefiecho "${firstnum} ${op}${secondnum}=$ ((${firstnum}${op}${secondnum})) "

Debugging:

[[email protected] 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=106+4=10[[email protected] scripts]# sh -x jisuan.sh 5 \* 5+   ' ['  3 -ne 3  '] ' + firstnum=5+ secondnum=5+ op= ' * ' ++ sed  ' s/[ 0-9]//g ' ++ echo 5+  ' ['  -n  '   '] ' +  ' ['   ' * '   '! = '  +  '] ' +   ' ['   ' * '   '! = '  -  '] ' +  ' ['   ' * '   '! = '   ' * '   '] ' ++ sed  ' /[0-9]//g ' ++ echo 5+  ' ['  -n  '   '] ' + echo  ' 5*5=25 ' 5*5=25 

Attention:

1. "-X" means debugging, and you can see the steps performed

2. The corresponding "*" needs to be escaped with "\"

This article is from the "Knowledge Change Destiny" blog, please be sure to keep this source http://ahtornado.blog.51cto.com/4826737/1927919

Shell Implements simple calculator function