If you need to refer the matched substring somewhere outside the current regular expression (for example, in another regular expression as a replacement string), you can retrieve it using the dollar sign $num, where num = 1.n. If you need to use the matched substring within the same regular expression, you can retrieve it using the backreference \num, where num = 1.n. Thus, a regex operator can be applied to the entire group. If a part of a regular expression is enclosed in parentheses, that part of the regular expression is grouped together. Matches subexpression and remembers the match. Matches any single character except a newline character. For example, a?ve? matches the ve in never. Matches the preceding character zero or one time. For example, "zo+" matches zoo but not z. Matches the preceding character one or more times. For example, "zo*" matches either z or zoo. Matches the preceding character zero or more times. The sequence \\ matches \ and \( matches (. Marks the next character as either a special character or a literal.
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