Patterns define the characters that match at a particular location by specifying a "character range". Character ranges are specified with a "bracket expression", which defines the allowed characters. For example, the following specifies that the character must be one of "a", "b", or "c":

[abcdef]

As a simple demonstration, a pattern that matches either grey or gray would be:

gr[ae]y

Contiguous ranges

When a range includes a contiguous sequence of characters the "-" operator can be used to express all characters in the specified range. For example, the preceding character range can also be expressed in the more compact form:

[a-f]

To include a literal "-" in a character range, place the "-" at either the beginning or the of the range. For example, to define range consisting of lower-case letters and a hyphen:

[a-z-]

Inverted Ranges

It can often be convenient to specify which characters do not match, by specifing an "inverted range". A range is inverted when the first character of a range is a "^" For example, to match words that do not include a, b, or c, one could use the character range:

[^a-c]

Character escapes

Character ranges can include some non-printable characters.

Pre-defined Ranges

Character ranges are a very convenient way to represent groups of characters. Some ranges are so common that there is an even shorter notation for them.

Meta-characters