Re: "jobs" command within substitution

["Matt Wozniski" <godlygeek@gmail.com>]

On 3/8/07, Micah Cowan wrote:
> Matt Wozniski wrote:
> > On 3/8/07, Micah Cowan wrote:
> >> Hello, all. This is my first post to this group.
> >>
> >> I scoured the manpages and list archives, but could not find the answer
> >> I seek.
> >>
> >> My question, in a nutshell, is: How can I effectively use the "jobs"
> >> builtin command in producing the interactive prompt?
> >
> > Rather than trying to parse the output of the 'jobs' command, you
> > might find yourself better suited by manipulating the variables
> > $jobdirs, $jobstates, and $jobtexts.  You correctly identified the
> > problem that you're hitting - $(jobs) is running in a subshell that
> > doesn't have any jobs in its job table.  I agree, however, that (jobs)
> > should also be blank, since it's also running in a subshell.  If,
> > however, you're dead-set on parsing the output of 'jobs', you could
> > use a syntax like 'jobs > >(read jobtext; echo $jobtext)', which is a
> > clever way to run jobs in the current shell and do the parsing in a
> > subshell via process substitution.
>
> Myself, I'd prefer to see both subshells produce the same output as the
> "current shell", as bash, pdksh and ksh do. However, dash goes the other
> way and makes ( jobs ) emit nothing (for all its claims of being a POSIX
> shell, though, dash is fairly broken in some respects, such as broken
> arithmetic expansion and lack of a line-editor [which POSIX requires]).
> I'd be interested in seeing what the OpenGroup committee has to say
> about it, since the standard is far from clear on the subject.
>
> I was not familiar with the variables you mention above. However, I'm
> not sure they solve the problem, as yet again, invoking them within a
> command-substitution will produce no information. The same problem would
> be true of using the other syntax you describe: I still have no
> available means to run the commands every time the prompt is issued,
> apart from within command substitution, which will kill the job-state
> info. Is there any way to get what I want executing in the "current" shell?
>
> Also, had you meant to post this reply to the list? It appears to have
> been sent to me only.

Yes, of course, I had meant to send it to the list.  My mistake.
*sheepish grin*.  So, you're right - the special variable $jobtexts
wouldn't match up in the subshell, but you could do something like
this:

$ function precmd {
export jt=""
for i in ${(kv)jobtexts}; jt="$jt:${i%% *}"
jt=${jt#:}
}

$ echo $jt
1:find:2:sleep

$ echo $(echo $jt)
1:find:2:sleep

And then you have a not-special, not-array version of jobtexts
exported into the environment of subshells that you can manipulate
however you want - and it even lets you remove the ugly dependence on
awk.  ;-)

(precmd is a function that gets called every time the editor is about
to display a prompt, FYI).

Like I said, though - even though this should take no effort
whatsoever to do with zsh - no more than 5 lines or so - it would be
difficult to maintain compatibility with bash.

The best way I can think of to do what you want, off the top of my
head, is the following:

function precmd {
  psvar[1]=""
  # For each key and each value in jobtexts
  for i in ${(kv)jobtexts}; do
    # Come up with a separator between psvar[1] and this text
    if [[ $sep == " " ]]; then
      sep=":"
    else
      sep=" "
    fi
    # Then tack it on to the end of psvar[1] - Removing from
    # the first space to the end of the element, if it has a space
    psvar[1]="${psvar[1]}$sep${i%% *}"
  done
  # Remove leading space we accidentally inserted
  psvar[1]=${psvar[1]# }
}

and

# Tell the prompt to reference psvar[1] (%?v == psvar[?])
PS1='micah(%1v)'

You don't even need to use prompt_subst.

Frankly, I'd just make your script check for ZSH right off the bat and
do it the simple way, leaving the complicated stuff for shells that
don't give you an elegant solution.

~Matt