HOW TO distiguish between command input and forked subshell ?

HOW TO distiguish between command input and forked subshell ?

[C. v. Stuckrad]

On Thu, 5 Sep 1996, Bart Schaefer ANSWERED:

> Subject: Re: HOW TO distiguish between command input and forked subshell ?

> On Sep 6, 12:47am, C. v. Stuckrad ASKED:
> > Subject: HOW TO distiguish between command input and forked subshell ?

> > Exactly, I want to have the function 'chpwd' give some output
> > if triggered by 'cd' or 'chdir' BUT TO GIVE NO OUTPUT
> > if triggered by cases like  '... $(cd somewhere; ls)...' 
*** this was exactly enough specified ***

> chpwd() {
>     if [[ -t 1 ]]
>     then
> 	print By golly, my standard output is a terminal.
>     fi
> }

OK, thanks for explaining (again), and this works perfectly well
in this case of ... $(cd ...)... !

The User who aked was a typical beginner, who used a macro/function
   chpwd () { ...to change x-window-title to the current dir... }
and now the title is no longer changed by cd-ing inside of $()
expansions. BUT if you just type '(cd somwhere; do_something)'
you again get the title changed to 'somewhere' instead of staying
where the zsh stood and stayed !

Does somebody see a chance to distinguish the two cases ?
I first thought $SHLVL, but it stays the same!
Does ...; ( something ) ; ...
the same as ... { something  } ; ...  ???

Again clueless (this time on zsh-users :-)  Stucki

Christoph von Stuckrad       * *  | talk to  | <stucki@math.fu-berlin.de> \
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Re: HOW TO distiguish between command input and forked subshell ?

[Bart Schaefer]

On Sep 7,  6:30pm, C. v. Stuckrad wrote:
} Subject: HOW TO distiguish between command input and forked subshell ?
}
} The User who aked was a typical beginner, who used a macro/function
}    chpwd () { ...to change x-window-title to the current dir... }
} and now the title is no longer changed by cd-ing inside of $()
} expansions. BUT if you just type '(cd somwhere; do_something)'
} you again get the title changed to 'somewhere' instead of staying
} where the zsh stood and stayed !

Don't change the title bar in chpwd().  Change the title bar in precmd().
If you want to avoid changing it "too frequently" for some reason, use

	if [[ ${oldPWD:=.} != $PWD ]]
	then
	    # ... change title bar and ...
	    oldPWD=$PWD
	fi

} Does somebody see a chance to distinguish the two cases ?
} I first thought $SHLVL, but it stays the same!

In older Bourne shells you used to be able to distinguish by using

	foo=$$; (if [ $$ -ne $foo ] ... ; )

because $$ would change inside the subshell.  But zsh doesn't do a new
getpid() for every $$ reference, so that doesn't work.  (This causes
other problems, because you used to be able to have a subshell kill
itself with `kill -1 $$` but in zsh that kills the parent.)

I don't know of any way to detect subshell-ness, having played with
it a bit in the past.



-- 
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