CODEWITHSUNDEEP
unixfilesystemsinode
DMAN
DMAN

Reputation: 13

Are the period commands "." and ".." actually referencing a file?

Since everything in Unix is a file, when we call "cd ." are we actually cding into the directory . ? Is it a protected symbolic reference to the parent directory of each directory?

Upvotes: 0

Views: 44

Answers (1)

hrishi
hrishi

Reputation: 433

Yes, everything in Unix, is a file. Like any directory, a file of any type, any device(speaker, keyboard,. etc.) and even a file-system itself, all act like a file for OS. In Unix every file has a inode attached with it, which contains the file metadata like info about permissions, size, time-stamps and most importantly file data block pointers which point to data block containing actual file data.

Hence each Directory(being a file) also has a inode. The content of the directory is the sequence of records. Each record has at least two fields which are filename and the inode number. 

file1name  file1_inode_number

Exact structure of record depends on the filesystem implementation. So basically directory file contain a (record)entry corresponding to each file and immediate sub-directory inside it. In addition to that, Directory file also contain 2 more entries which are 

.    :  mapped with self inode 
and 
..   :  mapped with parent's inode

so all over directory structure looks like 

.          inode_number_of_self
..         inode_number_of_parent_dir
file1name  inode_number_of_file1
file2name  inode_number_of_file2
.
.
so on

So whenever you cd ./ or cd ../ OS is referring current or parent directory(respectively) relative to your current directory.

Upvotes: 2

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