4.16. How do I convert a string to all lowercase or capital letters?

The easiest method is to use a new version of GNU sed, ssed, sedmod or sed16 and employ the \U, \L, or other switches on the right side of an s/// command. For example, to convert any word which begins with "reg" or "exp" into solid capital letters:

       sed -r "s/\<(reg|exp)[a-z]+/\U&/g"              # gsed4.+ or ssed
       sed "s/\<reg[a-z]+/\U&/g; s/\<exp[a-z]+/\U&/g"  # sed16 and sedmod

As you can see, sedmod and sed16 do not support alternation (|), but they do support case conversion. If none of these versions of sed are available to you, some sample scripts for this task are available from the Seder's Grab Bag:

       https://sed.sourceforge.net/grabbag/scripts

Note that some case conversion scripts are listed under "Filename manipulation" and others are under "Text formatting."