https://opensource.com/article/18/3/creating-bash-completion-script
an array variable used to store the completions. The completion mechanism uses this variable to display its contents as completions
COMPREPLY=( $(compgen -W "now tomorrow never" -- ${COMP_WORDS[COMP_CWORD]}) ) # propose given words at each let choose the first completion from given words and repeat it after (replace)
COMPREPLY=( $(compgen -W "now tomorrow never" "${COMP_WORDS[1]}") ) # let choose the first completion from given words and repeat it after (replace)