tr for Upper/Lower, Use ${foo,,}Seriously, if you are using Bash in 2021 or later you should be ashamed
of yourself for using tr subprocesses just to change the case of
something when they have been in Bash 4.0 parameter expansion since
the year 2009.
Here’s a reminder:
foo=${foo,,} # all lower
foo=${foo,} # initial lower
foo=${foo^^} # all upper
foo=${foo^} # initial upper
Of course if you don’t have that there’s always the POSIX compliant variety:
foo=$(echo "$foo" | tr "[:upper:]" "[:lower:]")