Any character used in a search or matching expression. For example, to find ind in windows the ind is a literal string; each character plays a part in the expression – it is literally the string you are searching for.

One or more special characters that have a unique meaning and are NOT used as literals. For example, in the search expression, the character ^ (circumflex or caret) is a metacharacter.

A way of indicating that you want to use a metacharacter as a literal. In a regular expression an escape sequence involves placing the metacharacter \ (backslash) in front of the metacharacter to be used as a literal. For example, to find ^ind in w^indow, use the search string \^ind. To find \\file in the string c:\\file, use the search string \\\\file, that is, each \ you are searching for (a literal) is preceded by an escape sequence \.

Term used to describe the string being searched for by the expression. In other words, the string in which you want to find a match or search pattern.

Term used to describe the expression being used to search the target string, that is, the pattern you use to find what you want.

Match anything inside the square brackets for one character position once and only once. For example, [12] means match the target to either 1 or 2 while [0123456789] means match to any character in the range 0 to 9.

When used inside square brackets acts as the 'range separator' and allows you to define a range. In the example above of [0123456789] you could rewrite it as [0-9]. You can define more than one range inside a list. For example, [0-9A-C] means check for 0 to 9 and A to C (but not a to c). Note: To test for a Dash inside brackets (as a literal), the Dash must come first or last. For example, [-0-9] will test for - (the Dash) and 0 to 9.

When used inside square brackets negates the expression (there is an alternate use for the circumflex/caret outside square brackets later). For example, [^Ff] means anything except upper or lower case F and [^a-z] means everything except lower case a to z.

When used outside square brackets, this symbol means look only at the beginning of the target string. For example, ^Win will not find Windows in STRING1 but ^Moz will find Mozilla.

The dollar symbol means look for the preceding text at the end of any line. For example, 'fox$' will match ‘silver fox’.

A “.” matches any character - though it does require that there is a character to match.

Matches the preceding character 0 or 1 times only. For example, colou?r will find both color and colour.

Matches the preceding character 0 or more times. For example, tr* will find tree and tread and trough.

Matches the previous character 1 or more times. For example, tre+ will find tree and tread but not trough.

Matches the preceding character n times exactly. For example, to find a local phone number, [0-9]{3}-[0-9]{4} would find any number of the form 123-4567.

The ( (open parenthesis) and ) (close parenthesis) may be used to group (or bind) parts of search expressions together, as shown in the examples.

Technically called alternation, this character means find the left hand OR right hand values. For example, gr(a|e)y will find gray or grey.