Unix Shell Script: Convert value of a variable to lowercase or uppercase

For example , we have a variable "check" as follows:

$ check="Unix Shell Script"

If you want to convert it into lowercase , it can be done as follows:

$ check=`echo $check | tr [:upper:] [:lower:]`

$ echo $check

unix shell script

Or if you want to convert it into uppercase , it can be done as follows:

 $ check=`echo $check | tr [:lower:] [:upper:]`

 impadmin@sourav:~$ echo $check

 UNIX SHELL SCRIPT