static wcstring path_create_data() {
    bool done = false;
    wcstring res;

    const env_var_t xdg_dir = env_get_string(L"XDG_DATA_HOME");
    if (!xdg_dir.missing()) {
        res = xdg_dir + L"/fish";
        if (!create_directory(res)) {
            done = true;
        }
    } else {
        const env_var_t home = env_get_string(L"HOME");
        if (!home.missing()) {
            res = home + L"/.local/share/fish";
            if (!create_directory(res)) {
                done = true;
            }
        }
    }

    if (!done) {
        res.clear();

        debug(0, _(L"Unable to create a data directory for fish. Your history will not be saved. "
                   L"Please set the $XDG_DATA_HOME variable to a directory where the current user "
                   L"has write access."));
    }
    return res;
}

/// Make sure the PATH variable contains something.
static void setup_path() {
    const env_var_t path = env_get_string(L"PATH");
    if (path.missing_or_empty()) {
        const wchar_t *value = L"/usr/bin" ARRAY_SEP_STR L"/bin";
        env_set(L"PATH", value, ENV_GLOBAL | ENV_EXPORT);
    }
}

static void update_export_array_if_necessary(bool recalc) {
    ASSERT_IS_MAIN_THREAD();
    if (recalc && !get_proc_had_barrier()) {
        set_proc_had_barrier(true);
        env_universal_barrier();
    }

    if (has_changed_exported) {
        std::map<wcstring, wcstring> vals;

        debug(4, L"env_export_arr() recalc");

        get_exported(top, &vals);

        if (uvars()) {
            const wcstring_list_t uni = uvars()->get_names(true, false);
            for (size_t i = 0; i < uni.size(); i++) {
                const wcstring &key = uni.at(i);
                const env_var_t val = uvars()->get(key);

                if (!val.missing() && val != ENV_NULL) {
                    // Note that std::map::insert does NOT overwrite a value already in the map,
                    // which we depend on here.
                    vals.insert(std::pair<wcstring, wcstring>(key, val));
                }
            }
        }

        std::vector<std::string> local_export_buffer;
        export_func(vals, local_export_buffer);
        export_array.set(local_export_buffer);
        has_changed_exported = false;
    }
}

static wcstring path_create_config() {
    bool done = false;
    wcstring res;

    const env_var_t xdg_dir = env_get_string(L"XDG_CONFIG_HOME");
    if (!xdg_dir.missing()) {
        res = xdg_dir + L"/fish";
        if (!create_directory(res)) {
            done = true;
        }
    } else {
        const env_var_t home = env_get_string(L"HOME");
        if (!home.missing()) {
            res = home + L"/.config/fish";
            if (!create_directory(res)) {
                done = true;
            }
        }
    }

    if (!done) {
        res.clear();

        debug(0, _(L"Unable to create a configuration directory for fish. Your personal settings "
                   L"will not be saved. Please set the $XDG_CONFIG_HOME variable to a directory "
                   L"where the current user has write access."));
    }
    return res;
}

/// Properly sets all locale information.
static void handle_locale(const wchar_t *env_var_name) {
    debug(2, L"handle_locale() called in response to '%ls' changing", env_var_name);
    const char *old_msg_locale = setlocale(LC_MESSAGES, NULL);
    const env_var_t val = env_get_string(env_var_name, ENV_EXPORT);
    const std::string &value = wcs2string(val);
    const std::string &name = wcs2string(env_var_name);
    debug(2, L"locale var %s='%s'", name.c_str(), value.c_str());
    if (val.empty()) {
        unsetenv(name.c_str());
    } else {
        setenv(name.c_str(), value.c_str(), 1);
    }

    char *locale = setlocale(LC_ALL, "");
    fish_setlocale();
    debug(2, L"handle_locale() setlocale(): '%s'", locale);

    const char *new_msg_locale = setlocale(LC_MESSAGES, NULL);
    debug(3, L"old LC_MESSAGES locale: '%s'", old_msg_locale);
    debug(3, L"new LC_MESSAGES locale: '%s'", new_msg_locale);
#ifdef HAVE__NL_MSG_CAT_CNTR
    if (strcmp(old_msg_locale, new_msg_locale)) {
        // Make change known to GNU gettext.
        extern int _nl_msg_cat_cntr;
        _nl_msg_cat_cntr++;
    }
#endif
}

/**
   When fishd isn't started, this function is provided to
   env_universal as a callback, it tries to start up fishd. It's
   implementation is a bit of a hack, since it evaluates a bit of
   shellscript, and it might be used at times when that might not be
   the best idea.
*/
static void start_fishd()
{
    struct passwd *pw = getpwuid(getuid());

    debug(3, L"Spawning new copy of fishd");

    if (!pw)
    {
        debug(0, _(L"Could not get user information"));
        return;
    }

    wcstring cmd = format_string(FISHD_CMD, pw->pw_name);

    /* Prefer the fishd in __fish_bin_dir, if exists */
    const env_var_t bin_dir = env_get_string(L"__fish_bin_dir");
    if (! bin_dir.missing_or_empty())
    {
        wcstring path = bin_dir + L"/fishd";
        if (waccess(path, X_OK) == 0)
        {
            /* The path command just looks like 'fishd', so insert the bin path to make it absolute */
            cmd.insert(0, bin_dir + L"/");
        }
    }
    parser_t &parser = parser_t::principal_parser();
    parser.eval(cmd, io_chain_t(), TOP);
}

/**
   Set up default values for various variables if not defined.
 */
static void env_set_defaults()
{

	if( env_get_string(L"USER").missing() )
	{
		struct passwd *pw = getpwuid( getuid());
		wchar_t *unam = str2wcs( pw->pw_name );
		env_set( L"USER", unam, ENV_GLOBAL );
		free( unam );
	}

	if( env_get_string(L"HOME").missing() )
	{
		const env_var_t unam = env_get_string( L"USER" );
		char *unam_narrow = wcs2str( unam.c_str() );
		struct passwd *pw = getpwnam( unam_narrow );
		wchar_t *dir = str2wcs( pw->pw_dir );
		env_set( L"HOME", dir, ENV_GLOBAL );
		free( dir );		
		free( unam_narrow );
	}	

	env_set_pwd();
	
}

/**
   Set up default values for various variables if not defined.
 */
static void env_set_defaults()
{

    if (env_get_string(L"USER").missing())
    {
        struct passwd *pw = getpwuid(getuid());
        if (pw->pw_name != NULL)
        {
            const wcstring wide_name = str2wcstring(pw->pw_name);
            env_set(L"USER", wide_name.c_str(), ENV_GLOBAL);
        }
    }

    if (env_get_string(L"HOME").missing())
    {
        const env_var_t unam = env_get_string(L"USER");
        char *unam_narrow = wcs2str(unam.c_str());
        struct passwd *pw = getpwnam(unam_narrow);
        if (pw->pw_dir != NULL)
        {
            const wcstring dir = str2wcstring(pw->pw_dir);
            env_set(L"HOME", dir.c_str(), ENV_GLOBAL);
        }
        free(unam_narrow);
    }

    env_set_pwd();

}

/// Insert a list of all dynamically loaded functions into the specified list.
static void autoload_names(std::set<wcstring> &names, int get_hidden) {
    size_t i;

    const env_var_t path_var_wstr = env_get_string(L"fish_function_path");
    if (path_var_wstr.missing()) return;
    const wchar_t *path_var = path_var_wstr.c_str();

    wcstring_list_t path_list;

    tokenize_variable_array(path_var, path_list);
    for (i = 0; i < path_list.size(); i++) {
        const wcstring &ndir_str = path_list.at(i);
        const wchar_t *ndir = (wchar_t *)ndir_str.c_str();
        DIR *dir = wopendir(ndir);
        if (!dir) continue;

        wcstring name;
        while (wreaddir(dir, name)) {
            const wchar_t *fn = name.c_str();
            const wchar_t *suffix;
            if (!get_hidden && fn[0] == L'_') continue;

            suffix = wcsrchr(fn, L'.');
            if (suffix && (wcscmp(suffix, L".fish") == 0)) {
                wcstring name(fn, suffix - fn);
                names.insert(name);
            }
        }
        closedir(dir);
    }
}

bool autoload_t::can_load(const wcstring &cmd, const env_vars_snapshot_t &vars) {
    const env_var_t path_var = vars.get(env_var_name);
    if (path_var.missing_or_empty()) return false;

    std::vector<wcstring> path_list;
    tokenize_variable_array(path_var, path_list);
    return this->locate_file_and_maybe_load_it(cmd, false, false, path_list);
}

void kill_add(const wcstring &str)
{
    ASSERT_IS_MAIN_THREAD();
    if (str.empty())
        return;

    wcstring cmd;
    wcstring escaped_str;
    kill_list.push_front(str);

    /*
       Check to see if user has set the FISH_CLIPBOARD_CMD variable,
       and, if so, use it instead of checking the display, etc.

       I couldn't think of a safe way to allow overide of the echo
       command too, so, the command used must accept the input via stdin.
    */

    const env_var_t clipboard_wstr = env_get_string(L"FISH_CLIPBOARD_CMD");
    if (!clipboard_wstr.missing())
    {
        escaped_str = escape(str.c_str(), ESCAPE_ALL);
        cmd.assign(L"echo -n ");
        cmd.append(escaped_str);
        cmd.append(clipboard_wstr);
    }
    else
    {
        /* This is for sending the kill to the X copy-and-paste buffer */
        if (!has_xsel())
        {
            return;
        }

        const env_var_t disp_wstr = env_get_string(L"DISPLAY");
        if (!disp_wstr.missing())
        {
            escaped_str = escape(str.c_str(), ESCAPE_ALL);
            cmd.assign(L"echo -n ");
            cmd.append(escaped_str);
            cmd.append(L" | xsel -i -b");
        }
    }

    if (! cmd.empty())
    {
        if (exec_subshell(cmd, false /* do not apply exit status */) == -1)
        {
            /*
               Do nothing on failiure
            */
        }

        cut_buffer = escaped_str;
    }
}

env_vars_snapshot_t::env_vars_snapshot_t(const wchar_t *const *keys) {
    ASSERT_IS_MAIN_THREAD();
    wcstring key;
    for (size_t i = 0; keys[i]; i++) {
        key.assign(keys[i]);
        const env_var_t val = env_get_string(key);
        if (!val.missing()) {
            vars[key] = val;
        }
    }
}

/// Properly sets all timezone information.
static void handle_timezone(const wchar_t *env_var_name) {
    debug(2, L"handle_timezone() called in response to '%ls' changing", env_var_name);
    const env_var_t val = env_get_string(env_var_name, ENV_EXPORT);
    const std::string &value = wcs2string(val);
    const std::string &name = wcs2string(env_var_name);
    debug(2, L"timezone var %s='%s'", name.c_str(), value.c_str());
    if (val.empty()) {
        unsetenv(name.c_str());
    } else {
        setenv(name.c_str(), value.c_str(), 1);
    }
    tzset();
}

/// Push all curses/terminfo env vars into the global environment where they can be found by those
/// libraries.
static void handle_curses(const wchar_t *env_var_name) {
    debug(2, L"handle_curses() called in response to '%ls' changing", env_var_name);
    const env_var_t val = env_get_string(env_var_name, ENV_EXPORT);
    const std::string &name = wcs2string(env_var_name);
    const std::string &value = wcs2string(val);
    debug(2, L"curses var %s='%s'", name.c_str(), value.c_str());
    if (val.empty()) {
        unsetenv(name.c_str());
    } else {
        setenv(name.c_str(), value.c_str(), 1);
    }
    // TODO: Modify input_init() to allow calling it when the terminfo env vars are dynamically
    // changed. At the present time it can be called just once. Also, we should really only do this
    // if the TERM var is set.
    // input_init();
}

wcstring expand_escape_variable(const env_var_t &var) {
    wcstring buff;
    wcstring_list_t lst;

    var.to_list(lst);
    if (lst.size() == 0) {
        ;  // empty list expands to nothing
    } else if (lst.size() == 1) {
        const wcstring &el = lst.at(0);

        if (el.find(L' ') != wcstring::npos && is_quotable(el)) {
            buff.append(L"'");
            buff.append(el);
            buff.append(L"'");
        } else {
            buff.append(escape_string(el, 1));
        }
    } else {
        for (size_t j = 0; j < lst.size(); j++) {
            const wcstring &el = lst.at(j);
            if (j) buff.append(L"  ");

            if (is_quotable(el)) {
                buff.append(L"'");
                buff.append(el);
                buff.append(L"'");
            } else {
                buff.append(escape_string(el, 1));
            }
        }
    }

    return buff;
}

/// Does this look like the escape sequence for setting a screen name.
static bool is_screen_name_escape_seq(const wchar_t *code, size_t *resulting_length) {
    bool found = false;
    if (code[1] == L'k') {
        const env_var_t term_name = env_get_string(L"TERM");
        if (!term_name.missing() && string_prefixes_string(L"screen", term_name)) {
            const wchar_t *const screen_name_end_sentinel = L"\x1b\\";
            const wchar_t *screen_name_end = wcsstr(&code[2], screen_name_end_sentinel);
            if (screen_name_end == NULL) {
                // Consider just <esc>k to be the code.
                *resulting_length = 2;
            } else {
                const wchar_t *escape_sequence_end =
                    screen_name_end + wcslen(screen_name_end_sentinel);
                *resulting_length = escape_sequence_end - code;
            }
            found = true;
        }
    }
    return found;
}

/**
   Check the X clipboard. If it has been changed, add the new
   clipboard contents to the fish killring.
*/
static void kill_check_x_buffer()
{
    if (!has_xsel())
        return;

    const env_var_t disp = env_get_string(L"DISPLAY");
    if (! disp.missing())
    {
        size_t i;
        wcstring cmd = L"xsel -t 500 -b";
        wcstring new_cut_buffer=L"";
        wcstring_list_t list;
        if (exec_subshell(cmd, list, false /* do not apply exit status */) != -1)
        {

            for (i=0; i<list.size(); i++)
            {
                wcstring next_line = escape_string(list.at(i), 0);
                if (i > 0) new_cut_buffer += L"\\n";
                new_cut_buffer += next_line;
            }

            if (new_cut_buffer.size() > 0)
            {
                /*
                  The buffer is inserted with backslash escapes,
                  since we don't really like tabs, newlines,
                  etc. anyway.
                */

                if (cut_buffer != new_cut_buffer)
                {
                    cut_buffer = new_cut_buffer;
                    kill_list.push_front(new_cut_buffer);
                }
            }
        }
    }
}

static void path_create(wcstring &path, const wcstring &xdg_var, const wcstring &which_dir,
                        const wcstring &custom_error_msg) {
    bool path_done = false;
    bool using_xdg = false;
    int saved_errno = 0;

    // The vars we fetch must be exported. Allowing them to be universal doesn't make sense and
    // allowing that creates a lock inversion that deadlocks the shell since we're called before
    // uvars are available.
    const env_var_t xdg_dir = env_get_string(xdg_var, ENV_GLOBAL | ENV_EXPORT);
    if (!xdg_dir.missing_or_empty()) {
        using_xdg = true;
        path = xdg_dir + L"/fish";
        if (create_directory(path) != -1) {
            path_done = true;
        } else {
            saved_errno = errno;
        }
    } else {
        const env_var_t home = env_get_string(L"HOME", ENV_GLOBAL | ENV_EXPORT);
        if (!home.missing_or_empty()) {
            path = home + (which_dir == L"config" ? L"/.config/fish" : L"/.local/share/fish");
            if (create_directory(path) != -1) {
                path_done = true;
            } else {
                saved_errno = errno;
            }
        }
    }

    if (!path_done) {
        maybe_issue_path_warning(which_dir, custom_error_msg, using_xdg, xdg_var, path,
                                 saved_errno);
        path.clear();
    }

    return;
}

//.........这里部分代码省略.........
                std::replace(val.begin(), val.end(), L':', ARRAY_SEP);
            }

            env_set(key, val.c_str(), ENV_EXPORT | ENV_GLOBAL);
        }
    }

    /* Set the given paths in the environment, if we have any */
    if (paths != NULL)
    {
        env_set(FISH_DATADIR_VAR, paths->data.c_str(), ENV_GLOBAL);
        env_set(FISH_SYSCONFDIR_VAR, paths->sysconf.c_str(), ENV_GLOBAL);
        env_set(FISH_HELPDIR_VAR, paths->doc.c_str(), ENV_GLOBAL);
        env_set(FISH_BIN_DIR, paths->bin.c_str(), ENV_GLOBAL);
    }

    /*
      Set up the PATH variable
    */
    setup_path();

    /*
      Set up the USER variable
    */
    if (env_get_string(L"USER").missing_or_empty())
    {
        const struct passwd *pw = getpwuid(getuid());
        if (pw && pw->pw_name)
        {
            const wcstring uname = str2wcstring(pw->pw_name);
            env_set(L"USER", uname.c_str(), ENV_GLOBAL | ENV_EXPORT);
        }
    }

    /*
      Set up the version variables
    */
    wcstring version = str2wcstring(get_fish_version());
    env_set(L"version", version.c_str(), ENV_GLOBAL);
    env_set(L"FISH_VERSION", version.c_str(), ENV_GLOBAL);

    /*
      Set up SHLVL variable
    */
    const env_var_t shlvl_str = env_get_string(L"SHLVL");
    wcstring nshlvl_str = L"1";
    if (! shlvl_str.missing())
    {
        wchar_t *end;
        long shlvl_i = wcstol(shlvl_str.c_str(), &end, 10);
        while (iswspace(*end)) ++end; /* skip trailing whitespace */
        if (shlvl_i >= 0 && *end == '\0')
        {
            nshlvl_str = to_string<long>(shlvl_i + 1);
        }
    }
    env_set(L"SHLVL", nshlvl_str.c_str(), ENV_GLOBAL | ENV_EXPORT);
    env_read_only.insert(L"SHLVL");

    /* Set up the HOME variable */
    if (env_get_string(L"HOME").missing_or_empty())
    {
        const env_var_t unam = env_get_string(L"USER");
        char *unam_narrow = wcs2str(unam.c_str());
        struct passwd *pw = getpwnam(unam_narrow);
        if (pw->pw_dir != NULL)
        {
            const wcstring dir = str2wcstring(pw->pw_dir);
            env_set(L"HOME", dir.c_str(), ENV_GLOBAL | ENV_EXPORT);
        }
        free(unam_narrow);
    }

    /* Set PWD */
    env_set_pwd();

    /* Set up universal variables. The empty string means to use the deafult path. */
    assert(s_universal_variables == NULL);
    s_universal_variables = new env_universal_t(L"");
    s_universal_variables->load();

    /* Set g_log_forks */
    env_var_t log_forks = env_get_string(L"fish_log_forks");
    g_log_forks = ! log_forks.missing_or_empty() && from_string<bool>(log_forks);

    /* Set g_use_posix_spawn. Default to true. */
    env_var_t use_posix_spawn = env_get_string(L"fish_use_posix_spawn");
    g_use_posix_spawn = (use_posix_spawn.missing_or_empty() ? true : from_string<bool>(use_posix_spawn));

    /* Set fish_bind_mode to "default" */
    env_set(FISH_BIND_MODE_VAR, DEFAULT_BIND_MODE, ENV_GLOBAL);

    /*
      Now that the global scope is fully initialized, add a toplevel local
      scope. This same local scope will persist throughout the lifetime of the
      fish process, and it will ensure that `set -l` commands run at the
      command-line don't affect the global scope.
    */
    env_push(false);
}

//.........这里部分代码省略.........
    global_env = top;
    global = &top->env;

    /*
      Now the environemnt variable handling is set up, the next step
      is to insert valid data
    */

    /*
      Import environment variables
    */
    for (char **p = (environ ? environ : __environ); p && *p; p++)
    {
        const wcstring key_and_val = str2wcstring(*p); //like foo=bar
        size_t eql = key_and_val.find(L'=');
        if (eql == wcstring::npos)
        {
            // no equals found
            env_set(key_and_val, L"", ENV_EXPORT);
        }
        else
        {
            wcstring key = key_and_val.substr(0, eql);
            wcstring val = key_and_val.substr(eql + 1);
            if (variable_can_be_array(val))
            {
                std::replace(val.begin(), val.end(), L':', ARRAY_SEP);
            }

            env_set(key, val.c_str(), ENV_EXPORT | ENV_GLOBAL);
        }
    }

    /* Set the given paths in the environment, if we have any */
    if (paths != NULL)
    {
        env_set(FISH_DATADIR_VAR, paths->data.c_str(), ENV_GLOBAL | ENV_EXPORT);
        env_set(FISH_SYSCONFDIR_VAR, paths->sysconf.c_str(), ENV_GLOBAL | ENV_EXPORT);
        env_set(FISH_HELPDIR_VAR, paths->doc.c_str(), ENV_GLOBAL | ENV_EXPORT);
        env_set(FISH_BIN_DIR, paths->bin.c_str(), ENV_GLOBAL | ENV_EXPORT);
    }

    /*
      Set up the PATH variable
    */
    setup_path();

    /*
      Set up the USER variable
    */
    const struct passwd *pw = getpwuid(getuid());
    if (pw && pw->pw_name)
    {
        const wcstring uname = str2wcstring(pw->pw_name);
        env_set(L"USER", uname.c_str(), ENV_GLOBAL | ENV_EXPORT);
    }

    /*
      Set up the version variables
    */
    wcstring version = str2wcstring(FISH_BUILD_VERSION);
    env_set(L"version", version.c_str(), ENV_GLOBAL);
    env_set(L"FISH_VERSION", version.c_str(), ENV_GLOBAL);

    const env_var_t fishd_dir_wstr = env_get_string(L"FISHD_SOCKET_DIR");
    const env_var_t user_dir_wstr = env_get_string(L"USER");

    wchar_t * fishd_dir = fishd_dir_wstr.missing()?NULL:const_cast<wchar_t*>(fishd_dir_wstr.c_str());
    wchar_t * user_dir = user_dir_wstr.missing()?NULL:const_cast<wchar_t*>(user_dir_wstr.c_str());

    env_universal_init(fishd_dir , user_dir ,
                       &start_fishd,
                       &universal_callback);

    /*
      Set up SHLVL variable
    */
    const env_var_t shlvl_str = env_get_string(L"SHLVL");
    wcstring nshlvl_str = L"1";
    if (! shlvl_str.missing())
    {
        long shlvl_i = wcstol(shlvl_str.c_str(), NULL, 10);
        if (shlvl_i >= 0)
        {
            nshlvl_str = to_string<long>(shlvl_i + 1);
        }
    }
    env_set(L"SHLVL", nshlvl_str.c_str(), ENV_GLOBAL | ENV_EXPORT);

    /* Set correct defaults for e.g. USER and HOME variables */
    env_set_defaults();

    /* Set g_log_forks */
    env_var_t log_forks = env_get_string(L"fish_log_forks");
    g_log_forks = ! log_forks.missing_or_empty() && from_string<bool>(log_forks);

    /* Set g_use_posix_spawn. Default to true. */
    env_var_t use_posix_spawn = env_get_string(L"fish_use_posix_spawn");
    g_use_posix_spawn = (use_posix_spawn.missing_or_empty() ? true : from_string<bool>(use_posix_spawn));
}