早期的 Unix Shell 是否使用过 `chd` 命令来切换目录？
3 分•作者: damiaozi•7 个月前
我一直在探索早期的 Unix 系统，特别是使用 SIMH 模拟器的 *PDP-7 上的 Unix V0* 及其后继版本 *PDP-11 上的 Unix V1*。<p>有趣的是，现代 shell 中最常用的命令之一 `cd` 在这些早期版本中 *并不* 存在。<p>- 在 *Unix V0* 中，目录切换是通过一个名为 `ch` 的 shell 命令完成的，该命令与一个名为 `dd`（directory directory，目录目录）的特殊目录结合使用。例如，要进入 Ken 的主目录，需要输入 `ch dd ken`。这似乎反映出当时还没有实现完整的层次文件结构。我已经在 SIMH 模拟器中验证了这种行为。<p>- 在 *Unix V1* 中，方法变得更加熟悉：你使用 `chdir /usr/ken`，但仍然 *不是* `cd`。这也在 SIMH 上得到了验证。Dennis Ritchie 在《Unix 分时系统的演变》中提到：<p>> “顺便说一句，_chdir_ 被拼写为 _ch_；我不记得当我们转向 PDP-11 时为什么会扩展它。”<p>现在，有趣的地方来了：<p>在阅读 [Unix V0 shell 源代码 (`pbsh.s`)](https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbsh.s#L199C1-L210C18) 时，我发现了一些似乎在检查与字符串 `“chdir”` 匹配的内置命令的东西——但它比较的是前 3 个字符，而不是 2 个或 5 个：<p>```asm
" https://github.com/DoctorWkt/pdp7-unix/blob/master/src/other/pbsh.s#L199C1-L210C18<p>chdirstr:
<ch>;<di>;<r 040<p>. . . . . .<p>" 检查内置的 "chdir" 命令
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>这种逻辑表明它应该匹配类似 `chd` 的字符串——因为只比较了前 3 个字符（`argv0`、`argv0+1`、`argv0+2`）。<p>然而，当在 SIMH 中运行 Unix V0 时，我只能让 `ch` 工作——`chd` 似乎没有被识别为命令。这似乎与 shell 源代码所暗示的相矛盾。<p>有人在早期的 Unix shell 中看到过 `chd` 被记录或工作吗？<p>很想听听其他探索过这一层 Unix 考古学的人的意见。
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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.