Allow specifying '{n}' as the OFFSET in the preview-window flag

[jaydee-coder]

This feature can be useful in scrolling to the selected line in the preview window.

For example, it can be used to use fzf as a quick filtering tool for large files while keeping an eye on the selected line as it shows up in the original file.

Example usage:

man fzf | tee /tmp/tmp.log | fzf \
  --reverse \
  --exact \
  --query 'position' \
  --preview 'bat --force-colorization /tmp/tmp.log --highlight-line $(({n}+1))' \
  --preview-window '+{n}/2'

[junegunn]

Merged, thanks!

[amariusz]

This is great! For really large text files, when bat fails to complete in reasonable time, I found such modified invocation especially useful:

man fzf | tee /tmp/tmp.log | fzf \
    --reverse \
    --exact \
    --query 'position' \
    --preview  'sed -n "$(( {n} - 150 )),$(( {n} + 150 ))p" /tmp/tmp.log | bat --force-colorization  --highlight-line 152 --language man' \
    --preview-window '+150/2'

This highlights and loads only a small relevant sample (300 lines) into preview window.
Of course swap man fzf with cat very_large_text_file | .. and use language of your choice.

Thanks!