#include <fcntl.h> #include <stdio.h> #include <string.h> #include <stdlib.h> #include <sys/stat.h> #define MAX_FILES 20 #define BUF_SIZE 1024 int main(int argc, char** argv) { int files[MAX_FILES] {}; size_t file_count = 0; int arg = 1; int oflag = O_WRONLY | O_CREAT; if (arg < argc && strcmp(argv[arg], "-a") == 0) { oflag |= O_APPEND; arg++; } else { oflag |= O_TRUNC; } for (int i = arg; i < argc; i++) { files[file_count] = open(argv[i], oflag, 0644); if (files[file_count] == -1) perror(argv[i]); else file_count++; if (file_count >= MAX_FILES) { fprintf(stderr, "only up to %d files are supported\n", MAX_FILES); break; } } char* buffer = (char*)malloc(BUF_SIZE); for (;;) { ssize_t nread = read(STDIN_FILENO, buffer, BUF_SIZE); if (nread == -1) perror("stdin"); if (nread <= 0) break; write(STDOUT_FILENO, buffer, nread); for (size_t i = 0; i < file_count; i++) write(files[i], buffer, nread); } free(buffer); if (ferror(stdin)) perror("stdin"); for (size_t i = 0; i < file_count; i++) close(files[i]); return 0; }