JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year SCRIPTING LANGUAGES Previous Question Paper (February/March - 2022 - R18)

In UNIX, a directory file is a specialized file that acts as a container for other files and directories. Unlike regular files that contain data, a directory file contains a list of mappings that associate filenames with their corresponding inode numbers.

The structure of a directory file is essentially a table with two primary columns: the filename and the inode number. When a user accesses a file by name, the system kernel reads the directory file to find the associated inode number, which then provides the metadata and physical location of the file on the disk.

Key characteristics include:

• It maintains the hierarchical structure of the file system.
• Every directory contains at least two entries: . (representing the current directory) and .. (representing the parent directory).
• Only the kernel can directly modify the contents of a directory file, while users interact with it through system calls like mkdir or rmdir.

The following commands are essential for directory management in UNIX environments:

• mkdir: Used to create a new directory.
  Example:

  mkdir project_files

  This creates a directory named 'project_files' in the current location.
• rmdir: Used to remove an empty directory. It will fail if the directory contains any files.
  Example:

  rmdir temp_folder

• chdir (cd): Used to change the current working directory to a specified path.
  Example:

  cd /home/user/documents

  This moves the user into the 'documents' folder.
• getcwd: This is typically a system call or a function used in programming (like Python or C) to retrieve the absolute path of the current working directory.
  Example (Python):

  import os
  print(os.getcwd())

  This prints the full path of the directory where the script is currently executing.