Expression Description \t Tab character. \n New line. . Matches any character. | Either expression on its left and right side matches the target string. For example, “a|b” matches “a” and “b”. [] Any of the enclosed characters may match the target character. For example, “[ab]” matches “a” and “b”. “[0-9]” matches any digit. [^] None of the enclosed characters may match the target character. For example, “[^ab]” matches all character EXCEPT “a” and “b”. “[^0-9]” matches any non-digit character. * Character to the left of asterisk in the expression should match 0 or more times. For example “be*” matches “b”, “be” and “bee”. + Character to the left of plus sign in the expression should match 1 or more times. For example “be+” matches “be” and “bee” but not “b”. ? Character to the left of question mark in the expression should match 0 or 1 time. For example “be?” matches “b” and “be” but not “bee”. ^ Expression to the right of ^ matches only when it is at the beginning of line. For example “^A” matches an “A” that is only at the beginning of line. $ Expression to the left of $ matches only when it is at the end of line. For example “e$” matches an “e” that is only at the end of line. () Affects evaluation order of expression and also used for tagged expression. \ scape character. If you want to use character “\” itself, you should use “\\”.