sed is a common Linux/Unix utility used to parse and transform text. Below are examples of uppercasing and lowercasing text with sed:

Uppercasing Text with sed

sed 's/[a-z]/\U&/g'

[a-z] is the regular expression which will match lowercase letters. \U& is used to replace these lowercase letters with the uppercase version.

Lowercasing Text with sed

sed 's/[A-Z]/\L&/g'

[A-Z] is the regular expression which will match uppercase letters. \L& is used to replace these uppercase letters with the lowercase version.