"Fallback" alias/function in zsh

"Fallback" alias/function in zsh

[Paul Moore]

Hi,
Is it possible to define a function which gets used whenever zsh's
normal alias/function/builtin/path lookup fails? The best example I can
give of what I'm after is using zsh for Win32 (which is version 3.0.5).
There, I'd like to have access to the good old CMD.EXE builtins, like
DIR (at the moment, I don't have a working Unix-like ls). So, I thought,
how about defining a function to be called "when all else fails" which
does "CMD /C <the command I typed>"? But I couldn't find a way of doing
this.

Is it possible, or if not, would it be a useful addition?

Paul Moore

Re: "Fallback" alias/function in zsh

[Bart Schaefer]

On Dec 8, 10:04pm, Paul Moore wrote:
> Subject: "Fallback" alias/function in zsh
>
> Is it possible to define a function which gets used whenever zsh's
> normal alias/function/builtin/path lookup fails?

In 3.1.5, there's the preexec() function, in which you could do something
like this:

  function preexec() {
    command=("$@")
  }
  function precmd() {
    (($?)) && CMD /C "$command[@]"
  }

That means, before executing the command, save it in $command; then, after
executing it (and just before printing the prompt) if the exit status was
nonzero, attempt to execute the command with CMD /C.

This will do unusual things when you execute compound commands (separated
with ; && || etc.) and won't work for backgrounded commands (&) but should
do what you want for simple commands typed at the prompt.

Of course, 3.1.5 isn't ported to Windows yet ...

Re: "Fallback" alias/function in zsh

[Phil Pennock]

Typing away merrily, Bart Schaefer produced the immortal words:
> In 3.1.5, there's the preexec() function, in which you could do something
> like this:
> 
>   function preexec() {
>     command=("$@")
>   }
>   function precmd() {
>     (($?)) && CMD /C "$command[@]"
>   }
[...]
> This will do unusual things when you execute compound commands (separated
> with ; && || etc.) and won't work for backgrounded commands (&) but should
> do what you want for simple commands typed at the prompt.

That seems dangerous.  The problem looks to be 'if path lookup fails'
not 'if path lookup fails or program returns non-zero'; could be fun to
run a grep(1) port and have it run twice if no matches were found ...
-- 
--> Phil Pennock ; GAT d- s+:+ a22 C++(++++) UL++++/I+++/S+++/H+ P++@ L+++
E-@ W(+) N>++ o !K w--- O>+ M V !PS PE Y+ PGP+ t-- 5++ X+ R !tv b++>+++ DI+ D+
G+ e+ h* r y?

Re: "Fallback" alias/function in zsh

[Bart Schaefer]

On Dec 9,  1:19am, Phil Pennock wrote:
} Subject: Re: "Fallback" alias/function in zsh
}
} Typing away merrily, Bart Schaefer produced the immortal words:
} > In 3.1.5, there's the preexec() function, in which you could do something
} > like this:
} > 
} >   function preexec() {
} >     command=("$@")
} >   }
} >   function precmd() {
} >     (($?)) && CMD /C "$command[@]"
} >   }
} 
} That seems dangerous.  The problem looks to be 'if path lookup fails'
} not 'if path lookup fails or program returns non-zero'; could be fun to
} run a grep(1) port and have it run twice if no matches were found ...

Easily enough adjusted:

  function precmd() {
    (($?)) && { whence "$command[1]" >& /dev/null || CMD /C "$command[@]" }
  }

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com