Creating regular expressions

. (period)

matches any single character

*  (asterisk)

matches zero or more instances of the previous pattern item

+ (plus sign)

matches one or more instances of the previous pattern item

? (question mark)

matches zero or one instance of the previous pattern item

(\ ) (backslash and parenthesis)

groups a subpattern
The repetition and alternation operators apply to the whole proceeding subpattern.

| (backslash and vertical bar or pipe)

alternation

[ ] (brackets)

delimit a set of characters
Ranges are specified as [x-y]. If the first character in the set is ^, then there is a match if the remaining characters in the set are not present.

^ (caret)

anchors the pattern to the beginning of the string
When the caret is used in a regular expression, the search only returns matches where the pattern occurs at the beginning of the string. For example, ^ab matches ab in the string abcdef, but will not find a match in the string cdefab.

$ (dollar sign)

anchors the pattern to the end of the string
When the dollar sign is used in a regular expression, the search only returns matches where the pattern occurs at the end of the string.

\& (backslash and ampersand)

connects two or more regular expressions as an 'AND' operator.
Regular expressions are connected as (x ) \& (y , where 'x' and 'y' are valid regular expressions. The backslash and ampersand character is never used as a regular expression. It is always used and functions only as a connector between two or more regular expressions.