unix – mkdir的“-p”选项

-p,--parents
    no error if existing,make parent directories as needed

用例示例：假设我要创建目录hello / goodbye但不存在：

$mkdir hello/goodbye
mkdir:cannot create directory 'hello/goodbye': No such file or directory
$mkdir -p hello/goodbye
$

-p同时创建，你好和再见

这意味着该命令将创建所有必需的目录来满足您的请求，如果该目录存在，则不返回任何错误。

关于rlidwka，Google对缩写词有非常好的记忆:)。我的搜索返回，例如：http://www.cs.cmu.edu/~help/afs/afs_acls.html

Directory permissions

l (lookup)
    Allows one to list the contents of a directory. It does not allow the reading of files. 
i (insert)
    Allows one to create new files in a directory or copy new files to a directory. 
d (delete)
    Allows one to remove files and sub-directories from a directory. 
a (administer)
    Allows one to change a directory's ACL. The owner of a directory can always change the ACL of a directory that s/he owns,along with the ACLs of any subdirectories in that directory. 

File permissions

r (read)
    Allows one to read the contents of file in the directory. 
w (write)
    Allows one to modify the contents of files in a directory and use chmod on them. 
k (lock)
    Allows programs to lock files in a directory.

因此，rlidwka意味着：所有权限。

值得一提的是，作为@KeithThompson在评论中指出，并不是所有的Unix系统都支持ACL。所以rididwka概念可能不适用于此。