Shortest match in regex from end

by

Use negative lookahead assertion.

foo(?:(?!foo).)*?boo

DEMO

(?:(?!foo).)*? – Non-greedy match of any character but not of foo zero or more times. That is, before matching each character, it would check that the character is not the letter f followed by two o‘s. If yes, then only the corresponding character will be matched.

Why the regex foo.*?boo matches the complete string fooxxxxxxfooxxxboo?

Because the first foo in your regex matches both the foo strings and the following .*? will do a non-greedy match upto the string boo, so we got two matches fooxxxxxxfooxxxboo and fooxxxboo. Because the second match present within the first match, regex engine displays only the first.

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