cp - copy files and directories
用法：
cp [OPTION] source dest
DESCRIPTION
Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.
-a 拷贝文件及属性
-i, --interactive
prompt before overwrite (overrides a previous -n option)
-l, --link
hard link files instead of copying
-n, --no-clobber
do not overwrite an existing file (overrides a previous -i option)
-R, -r, --recursive
copy directories recursively
-s, --symbolic-link
make symbolic links instead of copying
-u, --update
copy only when the SOURCE file is newer than the destination file or when the destination file is missing
-v, --verbose
explain what is being done
示例：
cp source dest
cp -a source dest
cp -r source/ dest/
