uppercase to lowercase in bash on a mac

in bash, you can use nocaseglob

shopt -s nocaseglob
for file in *.jpg *.jpeg *.gif
do
  echo "$file"
done
#turn off
shopt -u nocaseglob

in general to convert cases, various ways

echo "stRING" | awk '{print toupper($0)}'

echo "STRING" | tr "[A-Z]" "[a-z]" # upper to lower

echo "StrinNG" | sed 'y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/' #lower to upper

this is built into bash:

to convert $y into uppercase:

y="this Is A test"
echo "${y^^}"

and to convert $y into lowercase:

y="THIS IS a TeSt"
echo "${y,,}"

$ echo 'this IS some TEXT' | tr '[:upper:]' '[:lower:]'
this is some text