Sort Numbers from File Using Unix Pipes in C

// C Program to illustrate how to sort numbers from file using unix pipes

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <fcntl.h>

#define buffer 1024

int main(int argc, char *argv[]) {
    int id, fd[2];
    char my_copy[buffer];

    // Check if the user provides the correct number of arguments
    if (argc != 2) {
        printf("Usage: %s <input_file>\n", argv[0]);
        exit(1);
    }

    // Create a pipe
    if (pipe(fd) == -1) {
        perror("Pipe creation failed");
        exit(2);
    }

    // Fork a child process
    id = fork();

    // Check for fork errors
    if (id == -1) {
        printf("An error occurred with fork\n");
        exit(3);
    }

    // Child process
    if (id == 0) {
        //Close read of the pipe
        close(fd[0]);

        //redirect stdout to pipe
        dup2(fd[1], STDOUT_FILENO);

        //execute 'sort' command
        execlp("sort", "sort", "-n", argv[1], NULL);
        perror("Error calling execl");
        exit(4);
    } else {
        // Parent process

        //Close write of the pipe 
        close(fd[1]);

        //wait for the child process to finish
        wait(NULL);

        // Open the read the pipe as a file
        FILE *pipe_fd = fdopen(fd[0], "r");

        // Checking if the pipe is null
        if (pipe_fd == NULL) {
            perror("fdopen");
            exit(5);
        }
        
        // Reading the data from the pipe and print them
        while ((fgets(my_copy, sizeof(my_copy), pipe_fd)) != NULL) {
            //Checks when there is a line break and prints the data
            if (strchr(my_copy, '\n') != NULL) {
                printf("Data received through pipe:%s", my_copy);
            }
        }

        // Close the FILE 
        fclose(pipe_fd);
    }

    return 0;
}