Uppercase last n characters of every line in a wordlist regexp

Question

I'm looking for a way to uppercase the last n characters of every line in a wordlist, using regular expression. Example with n=3:

Input:

thisisatest
uppercasethelast3characters

Desired output:

thisisatEST
uppercasethelast3charactERS

Answer 1

Use this GNU sed:

sed -e 's/^\(.*\)\(.\{3\}\)$/\1\U\2/' file

With extended regex:

sed -r 's/^(.*)(.{3})$/\1\U\2/' file

Test:

$ sed -e 's/^\(.*\)\(.\{3\}\)$/\1\U\2/' file
thisisatEST
uppercasethelast3charactERS