Re: DEBUG_CMD_LINE (Was Re: PATCH: skip command from debug trap)

[Peter Stephenson <pws@csr.com>]

On Thu, 7 Aug 2008 10:31:40 +0100
Stephane Chazelas <Stephane_Chazelas@yahoo.fr> wrote:
> On Thu, Aug 07, 2008 at 09:54:41AM +0100, Peter Stephenson wrote:
> [...]
> > It would be possible with a bit of fiddling to get the DEBUG trap to happen
> > at the level of elements of a sublist, i.e. commands separated by && and
> > ||, but I'm not sure if that's worth it.  Beyond that you run into the
> > hideous complexity of pipelines and I don't think it can be pushed that far
> > down.
> [...]
> 
> But see how PS4 is expanded for every command:
> $ zsh -o PROMPT_SUBST -c 'PS4="\$(od -vAn -N2 -x /dev/urandom) "
>                           set -x; : a | : b; : c && : d'
>  4542 : a
>  e866 : b
>  a7ad : c
>  6051 : d

Yes, there are printprompt4()'s scattered all over the code.  However, PS4
doesn't interact with code execution as debug traps do.

> BTW, shouldn't PROMPT_SUBST be enabled by default in sh and ksh
> emulation?

If they do that, then presumably yes.

> Is there a way to run shell code (other than assignments and
> arithmetic expansion) upon the expansion of PS4? I thought of
> /(e:code:), but in scalar context I couldn't find a way for
> globbing to be performed.

I don't see how this differs from the stuff in $(...), which is treated as
a complete command line.  Do you mean you need code to run within
the current shell?

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070