Merge pull request #1 from LYC1929/master

simple shell function
add Iteration_2_History_Pipe folder, which contain a C program to implement history and pipe functions
Delete .DS_Store
Delete ._.DS_Store
Delete ._History_Pipe.c
Delete ._README.md
Merge pull request #6 from shilianzhu/master

Add Iteration_2_History_Pipe folder, which contain a C program to implement history and pipe functions