Env var / dynamic way to determine the preview hidden state within a transformer

[ibhagwan]

Checklist

• I have read through the manual page (man fzf)
• I have searched through the existing issues
• For bug reports, I have checked if the bug is reproducible in the latest version of fzf

Output of fzf --version

0.56.2

OS

• Linux
• macOS
• Windows
• Etc.

Shell

• bash
• zsh
• fish

Problem / Steps to reproduce

Context: #3817 (comment).

Consider the example (from the above link):

TRANSFORMER='
  echo -n change-preview-window:
  if ((100 * FZF_COLUMNS / FZF_LINES >= 150)) && ((FZF_COLUMNS >= 120)); then
    echo "right,50%,border-left"
  elif ((FZF_LINES >= 40)); then
    echo "up,30%,border-bottom"
  else
    echo "hidden"
  fi
'

fzf --bind "start:transform($TRANSFORMER),resize:transform($TRANSFORMER)" --preview 'cat {}' --preview-window=hidden

There are a couple of issues with this:

• When running the above the transfomer doesn't take into account the preview hidden state, due to the transform running on start, the previewer opens in a visible state even though we specify hidden
• Hiding the previewer with a keybind and resizing the terminal causes the previewer to unhide

I tried the below transformer (using FZF_PREVIEW_COLUMNS) but the previewer opens hidden and also hides itself when triggering resize:

TRANSFORMER='
  echo -n change-preview-window:
  if ((FZF_PREVIEW_COLUMNS == 0)) then
      echo "hidden"
  elif ((100 * FZF_COLUMNS / FZF_LINES >= 150)) && ((FZF_COLUMNS >= 120)); then
    echo "right,50%,border-left"
  elif ((FZF_LINES >= 40)); then
    echo "up,30%,border-bottom"
  else
    echo "hidden"
  fi
'

Am I missing something? Is there an env var I can use to determine if the previewer is hidden?

[junegunn]

No, there currently isn't a way. FZF_PREVIEW_* env vars are only exported to preview processes.

[ibhagwan]

No, there currently isn't a way. FZF_PREVIEW_* env vars are only exported to preview processes.

Would you consider exporting these to the transform process? Could there be any downside?

[junegunn]

Will do. No downsides. The overhead for adding environment variables to other processes is going to be negligible.

[ibhagwan]

Ty @junegunn!