Capturing STDOUT without subshells or file I/O

[Ben Klein <robobenklein@gmail.com>]

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Hello Zshellers,

I have an interesting predicament, I with to capture the STDOUT (builtin
printf) of a ZSH function to a variable, in which the function should be
running in the current shell context.

Currently, I have this:

  p10k_render_prompt_from_spec p10k_left p10k_opts > $tmpd/prompt
  read -d $'\0' _P10K_RENDERED_OUTPUT_PROMPT < $tmpd/prompt
  p10k_render_prompt_from_spec p10k_right p10k_opts right > $tmpd/prompt
  read -d $'\0' _P10K_RENDERED_OUTPUT_RPROMPT < $tmpd/prompt

And that involves creating a temporary file (/tmp) which might be
mounted on a spinning drive, so performance might take a hit.

The other route using a pipe:

p10k_render_prompt_from_spec p10k_left p10k_opts | read -d $'\0'
_P10K_RENDERED_OUTPUT_PROMPT

Causes environment variables and changes made during the `render_prompt`
call to be ignored. (Ends up in a subshell...?)

Is there some way I can use a virtual FD, or perhaps Zsh provides some
kind of buffer I could use instead?

In the end, I'm looking for a way to connect STDOUT to STDIN between ZSH
functions/builtins without any subshells or file I/O. (It's fine if it
gets buffered until close-of-stream.)

-- 
*\Ben Klein*
Founder and Owner of Robosane, robobenklein@robosane.net
You can find me elsewhere online as 'robobenklein'.
If you need to contact me securely, I am also reachable via GPG, or on
Keybase.

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