JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III LINUX PROGRAMMING Previous Question Paper (March - 2021 - R15)

These utilities are used for file comparison but serve different purposes:

• cmp: Performs a byte-by-byte comparison of two files. It is the fastest way to check if files are identical. It outputs the byte and line number where the first difference occurs and exits silently if the files are identical.
• diff: Performs a line-by-line comparison. It provides a detailed list of instructions (add, change, delete) required to transform one file into the other. It is primarily used for generating patches or viewing textual differences.
• comm: Compares two sorted files line-by-line and produces a three-column output: lines unique to the first file, lines unique to the second file, and lines common to both. It requires the input files to be pre-sorted.

A directory in Linux is a special file that contains a list of mappings between filenames and their corresponding inode numbers. Each entry in this list consists of the filename and the inode index, which links to the actual file metadata and data blocks on the disk.

The cp, mv, and rm commands update these directory entries as follows:

• cp: Creates a new entry in the destination directory with a new inode number. It allocates new data blocks and copies the contents of the source file into them.
• mv: If moving within the same filesystem, it simply renames the entry by updating the directory list (changing the filename associated with the existing inode). If moving across filesystems, it behaves like a cp followed by an rm.
• rm: Removes the filename entry from the directory list and decrements the link count of the associated inode. If the link count reaches zero, the system marks the inode and its associated data blocks as free for future use.