regex to remove particular string code example

Example 1: regex exclude character

[^a]	#any character except 'a'
[^aA]	#any character except 'a' or 'A'
[^a-z]	#any character except a lower case character
[^.]	#any character not a period

Example 2: deletes lines including regex match

Use d option at the end of sed replace definition for deleting line of matches.
sed -i "" "s/matching_pattern/d" file.txt