Convert all characters to lowercase
sed 's/\(.*\)/\L\1/g' some-file.txt
Convert all characters to uppercase
sed 's/\(.*\)/\U\1/g' some-file.txt
Capitalize first word, making everything lowercase
sed 's/\(.\)\(.*\)/\U\1\L\2/g' some-file.txt
Capitalize first letter of each word
sed 's/\b\(.\)/\U\1/g' some-file.txt
Find words and group them inside parenthesis
$ cat input.txt | sed 's/[A-Za-z]*/(&)/g'
(The) (quick) (brown) (fox) (jumps) (over) (the) (lazy) (dog)