什么是“邮件”，它是如何导航的？

Question

该程序位于/usr/bin/mail. 执行后，Version 8.1.2 01/15/2001显示。

输入list产品：

Commands are:
next, alias, print, type, Type, Print, visual, top, touch, preserve, 
delete, dp, dt, undelete, unset, mail, mbox, pipe, |, more, page, More, 
Page, unread, Unread, !, copy, chdir, cd, save, source, set, shell, 
version, group, write, from, file, folder, folders, ?, z, headers, 
help, =, Reply, Respond, reply, respond, edit, echo, quit, list, xit, 
exit, size, hold, if, else, endif, alternates, ignore, discard, retain, 
saveignore, savediscard, saveretain, core, #, inc, new

输入?产品：

Mail Command               Description
-------------------------  --------------------------------------------
t [message list]           type message(s).
n                          goto and type next message.
e [message list]           edit message(s).
f [message list]           give head lines of messages.
d [message list]           delete message(s).
s [message list] <file>    append message(s) to file.
u [message list]           undelete message(s).
R [message list]           reply to message sender(s).
r [message list]           reply to message sender(s) and all recipients.
p [message list]           print message list.
pre [message list]         make messages go back to /var/mail.
m <recipient list>         mail to specific recipient(s).
q                          quit, saving unresolved messages in mbox.
x                          quit, do not remove system mailbox.
h                          print out active message headers.
!                          shell escape.
| [msglist] command        pipe message(s) to shell command.
pi [msglist] command       pipe message(s) to shell command.
cd [directory]             chdir to directory or home if none given
fi <file>                  switch to file (%=system inbox, %user=user's
                           system inbox).  + searches in your folder
                           directory for the file.
set variable[=value]       set Mail variable.

Enterz显示消息列表的结尾 - 但该命令未显示在?帮助页面中。

1. 这是什么程序？
2. 有使用教程吗？
3. 有哪些常用命令和有用的技巧？
4. 如何导航（与 相反z）或刷新消息列表？

说明：这个问题是关于交互式程序的，而不是关于可编写脚本的命令——即在mail没有标志或参数的情况下在终端中输入的结果。

Answer 1

这个页面详细描述了交互式命令，实际上是一个相当全面的教程。描述诸如z和 之类的命令z-：

If there is more than a screenful of messages, then z will
show the next screenful, and z- will show the previous screenful.

Answer 2

mail不是松树；它只是mail。在一个完美的世界中，您的版本mail应该与POSIX/SUS 的mailx程序兼容（最相关的文档在“扩展描述”标题下），但是，像往常一样，确定与完美的偏差留给读者作为练习。