Very fast yes command (4x as fast as gnu coreutils)

yes

#include <cstdio>
#include <cstring>
#include <string>
#include "unistd.h"
 
#ifndef _BUF_SZ__
#define _BUF_SZ__ 1 << 16
#endif
 
int main(int argc, char *argv[]) {
    const char *val(argc > 1 ? argv[1]: "y");
    std::string data;
    while(data.size() + std::strlen(val) < _BUF_SZ__) data += val, data += '\n';
    while(write(STDOUT_FILENO, data.data(), data.size()));
    return EXIT_FAILURE;
}