早期的Unix Shell是否曾使用`chd`命令来更改目录？
我一直在探索早期的Unix系统，特别是*PDP-7上的Unix V0*及其后继版本*PDP-11上的Unix V1*，并使用SIMH模拟器进行研究。
有趣的是，在这些早期版本中，现代最常用的shell命令之一`cd`并不存在。
- 在*Unix V0*中，目录的更改是通过一个名为`ch`的shell命令来完成的，结合一个特殊的目录`dd`（directory directory）使用。例如，要进入Ken的主目录，可以输入`ch dd ken`。这似乎反映出当时尚未实现完整的层次文件结构。我已经在SIMH模拟器中验证了这一行为。
- 在*Unix V1*中，方法变得更加熟悉：你可以使用`chdir /usr/ken`，但仍然*不是*`cd`。这一点在SIMH中也得到了验证。丹尼斯·里奇在《Unix时间共享系统的演变》中提到：
> “顺便提一下，_chdir_被拼写为_ch_；我不记得为什么在转到PDP-11时要扩展这个名称。”
现在事情变得有趣了：
在阅读[Unix V0的shell源代码（`pbsh.s`）](https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbsh.s#L199C1-L210C18)时，我发现了一些似乎是在检查与字符串`"chdir"`匹配的内置命令的代码——但它比较的是前3个字符，而不是2个或5个：
```asm
chdirstr:
<ch>;<di>;<r 040
. . . . .
" check for built-in "chdir" command
lac argv0
sad chdirstr
skp
jmp 1f
lac argv0+1
sad chdirstr+1
skp
jmp 1f
lac argv0+2
sad chdirstr+2
jmp changedir
```
这个逻辑表明它会匹配像`chd`这样的字符串——因为只比较了前3个字符（`argv0`，`argv0+1`，`argv0+2`）。
然而，当我在SIMH中运行Unix V0时，我只能让`ch`工作——`chd`似乎并没有被识别为命令。这似乎与shell源代码所暗示的相矛盾。
有没有人见过`chd`在早期Unix shell中被记录或工作的情况？
我很想听听其他探索过这一层Unix考古学的人的看法。
查看原文
I've been exploring early Unix systems, particularly *Unix V0 on the PDP-7* and its successor, *Unix V1 on the PDP-11*, using the SIMH emulator.<p>Interestingly, one of the most common modern shell commands, `cd`, did *not* exist in these early versions.<p>- In *Unix V0*, directory changes were done via a shell command called `ch`, used in combination with a special directory called `dd`（directory directory）. For example, to enter Ken's home directory, one would type `ch dd ken`. This seems to reflect that a full hierarchical file structure hadn't been implemented yet. I've verified this behavior in the SIMH emulator.<p>- In *Unix V1*, the method becomes more familiar: you use `chdir /usr/ken`, though still *not* `cd`. This is also verified on SIMH. Dennis Ritchie mentioned in _"The Evolution of the Unix Time-sharing System"_:<p>> "Incidentally, _chdir_ was spelled _ch_; why this was expanded when we went to the PDP-11 I don't remember."<p>Now here's where it gets curious:<p>While reading the [Unix V0 shell source code (`pbsh.s`)](https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbsh.s#L199C1-L210C18), I found something that seems to check for a built-in command matching the string `"chdir"` — but compares the first 3 characters, NOT 2 or 5:<p>```asm
" https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbsh.s#L199C1-L210C18<p>chdirstr:
<ch>;<di>;<r 040<p>. . . . . .<p>" check for built-in "chdir" command
lac argv0
sad chdirstr
skp
jmp 1f
lac argv0+1
sad chdirstr+1
skp
jmp 1f
lac argv0+2
sad chdirstr+2
jmp changedir
```<p>This logic suggests it would match a string like `chd` — since only the first 3 characters are compared (`argv0`, `argv0+1`, `argv0+2`).<p>However, when running the Unix V0 in SIMH, I can only get `ch` to work — `chd` doesn't appear to be recognized as a command. This seems contradictory with what the shell source implies.<p>Has anyone seen `chd` documented or working in early Unix shells?<p>Would love to hear from others who have explored this layer of Unix archaeology.