Make use of zsh/mapfile to avoid more subshells

[AndydeCleyre]

To find candidates for changing, try rg '\(<\$'

[AndydeCleyre]

$ zmodload zsh/mapfile

$ setopt extendedglob

$ non_empty_lines=(${(f)mapfile[lines.txt]%$'\n'})

$ without_comments=(${non_empty_lines:# #\###*})

$ man zshmodules