ps 명령어의 원리?

    dir = opendir("/proc");
    if (!dir)
        error_msg_and_die("Can't open /proc");

    printf("%5s %-7s %-8s %6s %5s %s\n", "PID", "TTY", "Uid",
            "Size", "State", "Command");
    while ((entry = readdir(dir)) != NULL) {
        if (!isdigit(*entry->d_name))
            continue;
        sprintf(path, "/proc/%s/status", entry->d_name);
        if ((file2str(path, sbuf, sizeof sbuf)) != -1) {
            parse_proc_status(sbuf, &p);
        }

        sprintf(path, "/proc/%s/stat", entry->d_name);
        if ((file2str(path, sbuf, sizeof sbuf)) != -1) {
            parse_proc_stat(sbuf, &p);
        }

        /* Make some adjustments as needed */
        my_getpwuid(uidName, p.ruid);
        if (*uidName == '\0')
            sprintf(uidName, "%d", p.ruid);

        sprintf(path, "/proc/%s/cmdline", entry->d_name);
        file = fopen(path, "r");
        if (file == NULL)
            continue;
        i = 0;
        len = printf("%5d %-7s %-8s %6d   %c   ",
                p.pid, p.ttyname, uidName, p.vmsize, p.state);
        while (((c = getc(file)) != EOF) && (i < (terminal_width-len))) {
            i++;
            if (c == '\0')
                c = ' ';
            putc(c, stdout);
        }
        fclose(file);
        if (i == 0)
            printf("[%s]", p.cmd);
        putchar('\n');
    }
    closedir(dir);

snipped out from busybox.