用python的cmd模块写一个简单的shell

 from cmd import *
class MyShell(Cmd):
    def preloop(self):
        print "print this line before entering the loop"
            
    def postloop(self):
        print "print this line after leaving the loop"
    
    def precmd(self, line):
        print "print this line before do a command"
        return Cmd.precmd(self, line)
    
    def postcmd(self, stop, line):
        print "print this line after do a command"
        return Cmd.postcmd(self, stop, line)   
            
    def do_test(self, line):
        ''' test command, just print the arguments except some special ones'''
        if line == "exit":
            exit()
        else:
            print line
    
MyShell().cmdloop()
#继承cmd模块的Cmd类实现
#shell中的命令xx在类中对应的函数名为do_xx
#line是shell中输入的命令行参数