find string between characters
(?<=This is)(.*)(?=sentence)
I used lookbehind (?<=) and look ahead (?=) so that "This is" and "sentence" is not included in the match, but this is up to your use case, you can also simply write This is(.*)sentence.
(?<=src=")(.*)(?=")
https://stackoverflow.com/questions/6109882/regex-match-all-characters-between-two-strings