Note that you can also use

  opam config exec --switch=<SWITCH> -- <COMMAND>

to execute a command with a local switch choice. This is very helpful in
contexts where you don't exactly remember how to setup the environment (eg.
when prompted for an in-Emacs compilation command), or you want to play
with several versions alternatively in a single terminal (testing a
regression in new OCaml versions).

On Fri, Sep 19, 2014 at 9:21 AM, Louis Gesbert <louis.gesbert@ocamlpro.com>
wrote:

>  Le jeudi 18 septembre 2014, 17:20:37 Yotam Barnoy a écrit :
>
> > I have a question about opam. I would like to play with certain compiler
>
> > versions, but I don't want the switch to happen globally, because I still
>
> > need to compile regular code. Is it possible to switch to another
> compiler
>
> > locally (within a particular shell session) via environment variables,
>
> > while using my regular compiler in another shell session?
>
> >
>
> > If this is the way things work already, I apologize in advance -- it
>
> > appeared to me that running opam switch modifies some global state that
>
> > directly affects other pre-existing shell sessions.
>
> >
>
> > -Yotam
>
> >
>
> >
>
>
>
> This is already in our new FAQ [1] :)
>
> We're just waiting for 1.2 to be out before we post the new doc pages,
> because some of it doesn't apply to the current 1.1 stable release. OPAM
> 1.2 is still in RC stage.
>
>
>
>
>
> [1]
>
>
> http://opam.ocaml.org/doc/1.2/FAQ.html#CanIworkondifferentswitchesatthesametimeindifferentshells
>