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Write four different programs based on UNIX utilities: 1. mystat.c: Implement a version of the stat command that displays file size, block count, link count, permissions, and inode. 2. myls.c: List files in a directory, with optional detailed info when the -l flag is used, and default to the current directory if none is specified. 3. mytail.c: Print the last few lines of a file efficiently by seeking near the end and reading backwards. 4. mytree.c: Recursively traverse and print the directory tree starting from a given directory or current directory if none is provided. All programs must use appropriate system calls, include a makefile for compilation, and should be your original work with no copying from the internet. The code will be evaluated on correctness, API usage, organization, and style.

Sample Paper For Above instruction

In modern computing environments, understanding file system utilities is fundamental for system administrators, programmers, and advanced users. Writing custom versions of standard UNIX utilities deepens comprehension of underlying system calls, file handling, directory structures, and the Linux/UNIX operating system's API. This paper discusses the implementation of four essential utilities—mystat, myls, mytail, and mytree—each serving a unique purpose in file system analysis and navigation, emphasizing their design, functionality, and system interface utilization.

Introduction

File system utilities are vital tools that allow users to inspect, manipulate, and navigate the complex hierarchy of files and directories in an operating system. The UNIX environment provides a rich set of system calls that facilitate direct interaction with the file system, including stat(), opendir(), readdir(), and lseek(). Re-implementing these utilities enhances understanding of these system calls and how they can be leveraged to create powerful command-line tools. This paper presents the design and implementation considerations of four such utilities: mystat, myls, mytail, and mytree.

MyStat Implementation

The mystat utility aims to replicate the behavior of the UNIX stat command, which outputs detailed metadata about a file. The core of this implementation involves calling stat() on the provided filename or directory name. The stat() system call fills a struct stat with information such as size, blocks allocated, link count, permissions, and inode number.

To display the file size, the program accesses st_size. The number of blocks is obtained via st_blocks. The link count is stored in st_nlink. Permissions are decoded from st_mode using bit masks, translating into human-readable permission strings. The inode number is present in st_ino. The implementation involves parsing user input, handling errors gracefully, and formatting output for clarity.

MyLs Development

The myls utility mimics the behavior of ls, listing files within a specified directory. When invoked without arguments, it defaults to the current working directory, retrieved via getcwd(). Using opendir() and readdir(), it reads directory entries and prints only filenames initially. When called with the -l flag and an optional directory argument, it displays detailed information for each entry, fetching data via stat().

The detailed output includes owner and group IDs, permissions, size, and modification times. Permissions are decoded similarly to mystat. Ensuring correct handling of directory reading, especially with symbolic links and hidden files, is critical. The utility demonstrates proficient use of directory API functions and string formatting for output.

MyTail Strategy

The mytail utility reads the last N lines of a file efficiently. The approach involves opening the file with open(), then using lseek() to move near the end of the file. It reads a block of data into memory, then scans backwards to locate newline characters, counting lines until reaching the specified number.

This method minimizes disk I/O by avoiding reading the entire file when unnecessary. Once the lines are identified, they are printed from the first of the last N lines to the end, preserving order. The implementation handles edge cases, such as very small files or files without newline characters, ensuring robustness and performance.

MyTree Recursive Directory Traversal

The mytree utility implements recursive directory traversal, similar to the UNIX tree command. Starting from a given directory or the current directory if none is specified, it lists all entries. For each directory found, it recursively calls itself to print subdirectories and files, thereby displaying a hierarchical view of the filesystem.

This utility employs directory functions like opendir() and readdir(), and when encountering subdirectories, it calls itself recursively, passing the subdirectory path. To prevent infinite loops, it handles symbolic links appropriately. The output formatting visually indicates directory levels, aiding readability. This recursive approach underscores the importance of stack management and clean API use in system programming.

Conclusion

Implementing these UNIX-like utilities from scratch provides valuable insights into system call functionality, file metadata management, directory traversal, and efficient I/O handling. Each utility leverages specific system interfaces to perform its tasks effectively, illustrating the power and flexibility of UNIX API calls. Understanding these foundational tools enhances both practical skills and theoretical knowledge of operating systems and file management, essential in system administration and software development environments.

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