008_file manage

1. cp : copy files and directories
    1.1 Basic use of cp  :   cp SRC DEST
        SRC is a single file：
            If DEST does not exist ：create DEST and copy the content of SRC to DEST；
            If DEST exists：
                If DEST is a file ：overwrite DEST , and -i option is recommanded；
                If DEST is a directory ：Create a file named SRC in the directory of DEST,and fill the new file with the content of source SRC；
        SRC are multiple files：
            DEST must exist and is a directory
        If SRC is a directory ：-r option is recommanded.
            If DEST does not exist ：Create a directory named DEST and copy all of the files in SRC to DEST.
            If DEST exists ：
                If DEST is a file ：An error is reported.
                If DEST is a directory：copy all of the files in SRC to DEST.
    1.2 Commondly used options
        -i：interactive
            -r, -R: recursion
        -a: 归档，相当于-dR --preserv=all

             The original state and attributes of copied files are not always saved,for example ,if you copy a symlink file,it actually copies not the symlink file itself,but create a file with the same name as the symlink file and then fill the new file with the content of the file linked by the symlink file.  -a is used to resolve this problem.    

        -p: --preserv=mode,ownership,timestamp
        -v: --verbose
            -f: --force
2. mv : move (rename) files
    2.1 The same basic use as cp
    2.2 Commondly used options
        -i: interactive
               -f: forced
3. rm : remove files or directories
    3.1 Basic use of rm：rm [OPTION]... FILE...
    3.2 Commondly used options
        -i: interactive
            -f: forced
            -r: recursion
            rm -rf