Because the default linux shell: when / bin / bash, at run time there will be a lot of default is a character special symbols or parameters, so in order to create an ordinary file a special function symbols, they need to be changed
for example want to create a contained '-a' Trivial file
first method:
· './'相当于重新创建了一个新的shell，不继承当前shell的环境变量的值，同样若在程序中改变了环境变量的值，不会同步到默认的shell中；
· 新的shell不会把'-a'当成是一个参数，而是普通的字符处理；
The second method:
