split() {
   # Usage: split "string" "delimiter"
   IFS=$'
' read -d "" -ra arr <<< "${1//$2/$'
'}"
   printf '%s
' "${arr[@]}"
}

$ split "apples,oranges,pears,grapes" ","
apples
oranges
pears
grapes

$ split "1, 2, 3, 4, 5" ", "
1
2
3
4
5

# Multi char delimiters work too!
$ split "hello---world---my---name---is---john" "---"
hello
world
my
name
is
john

lower() {
    # Usage: lower "string"
    printf '%s
' "${1,,}"
}

$ lower "HELLO"
hello

$ lower "HeLlO"
hello

$ lower "hello"
hello

upper() {
    # Usage: upper "string"
    printf '%s
' "${1^^}"
}

$ upper "hello"
HELLO

$ upper "HeLlO"
HELLO

$ upper "HELLO"
HELLO