There are a few different ways to convert uppercase letters to lowercase.
One way is using the tr command. The example below demonstrates how you can use tr to convert to lowercase.
tr ‘[:upper:]’ ‘[:lower:]’ < myfile
This will convert this input file:
# cat myfile
ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz
to this:
abcdefghijklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxyz
An alternate way is using this syntax:
tr ‘[A-Z]’ ‘[a-z]’ < myfile