How to convert a string to lower case in Bash?

Question

Is there a way in bash to convert a string into a lower case string?

For example, if I have:

a=\"Hi all\"

I want to convert it to:<

Answer 1

Using GNU sed:

sed 's/.*/\L&/'

Example:

$ foo="Some STRIng";
$ foo=$(echo "$foo" | sed 's/.*/\L&/')
$ echo "$foo"
some string

Answer 2

In bash 4 you can use typeset

Example:

A="HELLO WORLD"
typeset -l A=$A