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I have a script at /venv/bin/activate that sets some environment variables. I’m looking for a way to start zsh, have it source this script, and then continue with a normal interactive session. When I exit this session, the session I return to should not know about any of the environment changes that activate made. How can I invoke zsh like this?

(This is pretty much the same question as this one, except that I’m using zsh instead of bash.)

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If the activate script only sets environment variables, you can read it in one shell, then execute a new, interactive zsh instance.

sh -c '. /venv/bin/activate; exec zsh -i'

The wrapper shell sh can be replaced by any shell that is able to parse /venv/bin/activate, including zsh if the activate script is compatible with it.

In addition to environment variables, the interactive zsh instance will inherit the process ID and a few other process settings such as resource limits (ulimit …) and ignored signals (trap '' …). On the other hand, settings of the shell itself are not preserved: shell variables (var=… if var is not exported), shell options (set -… or shopt …), key bindings, alias and function definitions, etc.

  • This is a good solution as long as you don’t need to return to the original shell afterward (and as long as the effects of activate fall into only the categories you mentioned). – bdesham Sep 6 at 20:45
  • @bdesham Yes, I meant that you should run that as a separate shell script but I can see that it isn't clear, I'll clarify. – Gilles 'SO- stop being evil' Sep 6 at 20:56
  • Oh, even better. Thanks for clarifying. – bdesham Sep 6 at 21:40
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Using ZDOTDIR

Create a (possibly temporary) directory at, say, /venv_startup that contains two files, .zshenv and .zshrc. The .zshenv file consists of

source ~/.zshenv
source /venv/bin/activate

while .zshrc says

source ~/.zshrc

Now, invoke zsh via

ZDOTDIR=/venv_startup zsh

This says to zsh, “instead of starting out by sourcing the .zshenv and .zshrc files in $HOME, source the files of those names in /venv_startup instead.” Since the versions in /venv_startup source the ones in $HOME anyway, the net effect is that the shell will run

source /venv/bin/activate

in between executing your zshenv and your zshrc. After that, it will be a normal interactive session.

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