These are basically the special characters or escape characters. The backslash character (\) in a regular expression indicates that the character that follows it either is a special character or should be interpreted literally.
The following table lists the escape characters:
| Escaped character | Description | Pattern | Matches |
|---|
| \a | Matches a bell character, \u0007. | \a | "\u0007" in "Warning!" + '\u0007' |
| \b | In a character class, matches a backspace, \u0008. | [\b]{3,} | "\b\b\b\b" in "\b\b\b\b" |
| \t | Matches a tab, \u0009. | (\w+)\t | "Name\t", "Addr\t" in "Name\tAddr\t" |
| \r | Matches a carriage return, \u000D. (\r is not equivalent to the newline character, \n.) | \r\n(\w+) | "\r\nHello" in "\r\Hello\nWorld." |
| \v | Matches a vertical tab, \u000B. | [\v]{2,} | "\v\v\v" in "\v\v\v" |
| \f | Matches a form feed, \u000C. | [\f]{2,} | "\f\f\f" in "\f\f\f" |
| \n | Matches a new line, \u000A. | \r\n(\w+) | "\r\nHello" in "\r\Hello\nWorld." |
| \e | Matches an escape, \u001B. | \e | "\x001B" in "\x001B" |
| \ nnn | Uses octal representation to specify a character (nnn consists of up to three digits). | \w\040\w | "a b", "c d" in "a bc d" |
| \x nn | Uses hexadecimal representation to specify a character (nn consists of exactly two digits). | \w\x20\w | "a b", "c d" in "a bc d" |
| \c X \c x | Matches the ASCII control character that is specified by X or x, where X or x is the letter of the control character. | \cC | "\x0003" in "\x0003" (Ctrl-C) |
| \u nnnn | Matches a Unicode character by using hexadecimal representation (exactly four digits, as represented by nnnn). | \w\u0020\w | "a b", "c d" in "a bc d" |
| \ | When followed by a character that is not recognized as an escaped character, matches that character. | \d+[\+-x\*]\d+\d+[\+-x\*\d+ | "2+2" and "3*9" in "(2+2) * 3*9"
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