tee.c

/**
 * Print size and contents of a PIPE
 * Author: David Coles <coles.david@gmail.com>
 */

#define _GNU_SOURCE

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>

#include <stdio.h>
#include <errno.h>
#include <string.h>

#define ERROR(FORMAT, ...) do { fprintf(stderr, "ERROR: " FORMAT "\n", __VA_ARGS__); } while(0)

int main(int argc, char* argv[])
{
    if (argc < 2) {
        fprintf(stderr, "usage: %s PIPE\n", argv[0]);
        return 2;
    }

    int fd = open(argv[1], O_RDONLY|O_NONBLOCK);
    if (fd < 0) {
        ERROR("open %s (%d)", strerror(errno), errno);
        return 1;
    }

    int size = -1;
    if (ioctl(fd, FIONREAD, &size) != 0) {
        ERROR("ioctl(FIONREAD) %s (%d)", strerror(errno), errno);
        close(fd);
        return 1;
    }

    printf("%d\n", size);
    if (size > 0) {
        ssize_t sz = tee(fd, STDOUT_FILENO, (int)-1, SPLICE_F_NONBLOCK);
        if (sz < 0) {
            ERROR("tee %s (%d)", strerror(errno), errno);
        }
    }

    close(fd);
    return 0;
}