modified tee test

mdup.c

#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#define check(v) \
    do { \
        if ((v) < 0) { \
            fprintf(stderr, "%s:%d: %s", __func__, __LINE__, strerror(errno)); \
            exit(EXIT_FAILURE); \
        } \
    } while (0)

void usage(const char* name)
{
    fprintf(stderr, "Usage: %s [-n 1/2] filename command\n", name);
    exit(EXIT_FAILURE);
}

int main(int argc, char **argv)
{
    int opt;
    int choosed_fileno = 1;
    while ((opt=getopt(argc, argv, "n:")) != -1) {
        switch (opt) {
        case 'n':
            choosed_fileno = atoi(optarg);
            if (choosed_fileno == 1 || choosed_fileno == 2)
                break;
        default:
            usage(argv[0]);
        }
    }
    if (optind >= argc) {
        usage(argv[0]);
    }
    int idx=optind;
    const char* filename = argv[idx];
    idx++;
    if (idx >= argc) {
        usage(argv[0]);
    }
    const char* comm_name = argv[idx];
    idx++;

    int pipe_fd[2], pipe_fd2[2];
    check(pipe(pipe_fd));
    check(pipe(pipe_fd2));

    const pid_t pid = fork();
    check(pid);
    if (pid == 0) {
        close(pipe_fd[0]);
        close(pipe_fd2[0]);
        dup2(pipe_fd[1],STDOUT_FILENO);
        dup2(pipe_fd2[1],STDERR_FILENO);
        execv(comm_name, &argv[idx]);
    } else {
        close(pipe_fd[1]);
        close(pipe_fd2[1]);
        FILE *logfile = filename? fopen(filename, "a") : NULL;
        if (filename && !logfile) {
            fprintf(stderr, "cannot open file: %s: %s\n", filename, strerror(errno));
            exit(EXIT_FAILURE);
        }

        char ch, ch2;
        int err, err2;
        err=read(pipe_fd[0],&ch,1);
        err2=read(pipe_fd2[0], &ch2, 1);
        do {
            if (err>0) {
                putchar(ch);
                if (ch == '\n')
                    fflush(stdout);
                if (choosed_fileno == 1) {
                    fputc(ch, logfile);
                    if (ch == '\n')
                        fflush(logfile);
                }
                err=read(pipe_fd[0],&ch,1);
            }
            if (err2>0) {
                putchar(ch2);
                if (ch2 == '\n')
                    fflush(stdout);
                if (choosed_fileno == 2) {
                    fputc(ch2, logfile);
                    if (ch2 == '\n')
                        fflush(logfile);
                }
                err2=read(pipe_fd2[0], &ch2, 1);
            }
        } while (err > 0 || err2 > 0);
        putchar('\n');
        fputc('\n', logfile);
        close(pipe_fd[0]);
        close(pipe_fd2[0]);
        fclose(logfile);
    }

    return EXIT_SUCCESS;
}