Quoting "dotenv" files.

_builtin.sh

dotenv list --format=shell

quote-dotenv.sed

#!/usr/bin/env -S sed -Ef

# Delete blank and commented-out lines.
/^[[:space:]]*(#|$)/ d

# Replace single quotes with the "unquote-escape-quote" trick:
#   1'2'3  →  '1'\''2'\''3'
# i.e. the concatenation of:
#   '1'  \'  '2'  \'  '3'
s/'/'\\''/g

# Wrap the right-hand side of each key=value line with single quotes.
s/=(.*)/='\1'/g

quote-dotenv.zsh

#!/usr/bin/env zsh

zmodload zsh/regex
setopt err_exit no_unset warn_create_global warn_nested_var re_match_pcre

function _quote_dotenv {
	local MATCH MBEGIN MEND    # created by =~
	local -a match mbegin mend # created by =~
	local line
	while read -r line; do
		if [[ ! "$line" =~ '^[[:space:]]*(#|$)' ]]; then
			print -r -- "${line%%=*}=${(q)${line#*=}}"
		fi
	done
}

if (( $# > 0 )); then
	for arg in "${@}"; do
		_quote_dotenv < "$arg"
	done
else
	_quote_dotenv
fi