Transform

STR="HELLO WORLD!"
echo ${STR,}   # => hELLO WORLD!
echo ${STR,,}  # => hello world!
STR="hello world!"
echo ${STR^}   # => Hello world!
echo ${STR^^}  # => HELLO WORLD!
ARR=(hello World)
echo "${ARR[@],}" # => hello world
echo "${ARR[@]^}" # => Hello World