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