Re: [9front] Re: /bin/"" use of rc -c instead of eval

[sirjofri <sirjofri+ml-9front@sirjofri.de>]

06.07.2024 11:43:32 Romano <me+unobe@fallglow.com>:
> Maybe I did not give enough context in my reply: I know
> that " lists *previous* commands and "" executes them. So
> 'cd /sys/src' was something I had previously run in that
> window. Here's a comparison of the current "" functionality:
>
> |cpu% cd /sys/src
> |cpu% cd /sys
> |cpu% pwd
> |/sys
> |cpu% " cd
> |   cpu% cd /sys/src
> |   cpu% cd /sys
> |cpu% "" cd.*src
> |    cpu% cd /sys/src
> |cpu% pwd
> |/sys
> |cpu%
>
> And here it is using "" as a fn with eval:
>
> |cpu% fn "" {
> |       PROMPT='[^  ]*(%|;)+[   ]+'
> |       _x=`{
> |           " $*|tail -1
> |       }
> |       if(~ $#_x 0){
> |           >[1=2]echo no such command found
> |           exit notfound
> |       }
> |       >[1=2]echo '    ' $_x
> |       _x=`{
> |           echo -n 'eval '''; echo $_x|sed 's/^'^$PROMPT^'//; s/''/''''/g; s/$/''/'
> |       }
> |       eval $"_x
> |   }
> |cpu% cd /sys/src
> |cpu% cd /sys
> |cpu% pwd
> |/sys
> |cpu% " cd
> |   cpu% cd /sys/src
> |   cpu% cd /sys
> |cpu% "" cd.*src
> |    cpu% cd /sys/src
> |cpu% pwd
> |/sys/src
> |cpu%
>
> Did you think I was saying it worked differently?

Initially, it sounded like that, but with that context you're right.

> My main point is that built-in rc commands don't
> like other commands with "". That is, even tho'
> it'll happily print out the cd command, it has
> no effect in the shell since it's run in a
> subshell. The most I could do is then copy-and-
> paste if I wanted to use it. AFAICT a handful
> would really make a difference with the fn-form
> of "": cd, eval, flag, fn, and '.'.

I don't think this has much to do with builtins or not, but with the subshell. Cd is changing "the namespace". I wonder how "" works with mounts/binds: do they also only change the namespace of the subshell? I'd guess they do.

>> Note that I never tested cd'ing with "", which means a lot. It's probably not as useful in most cases, which makes sense if you think about it: you use cd to switch to another directory. When you're there, running it again is a no-op at best, or it fails.
>
> Switching back and forth between different directories
> is a common occurrence during development for me, so
> I wanted something akin to bash-like 'cd -' or '^R cd'
> without having to use the mouse.

I usually have a single rc command at the end of my test scripts (or I run it manually). That way I can investigate/analyze the results, and just use ^D to fall back to my main shell. Sure that's not ideal for everyone, but when I call a program I wouldn't expect it to change my directory at all.

I often have a ramfs behind an rfork n, so I build my test scripts like this:

> #!/bin/rc
> rfork en
> ramfs
> # test...
> cd /tmp
> rc

sirjofri