POSIX Regular Expressions

POSIX (Portable Operating System Interface) defines a set of standard operating system interfaces based on the UNIX OS. In POSIX Basic Regex Expression (BRE) syntax, most characters are treated as literals (e.g. they match only themselves). However, some characters called metacharacters have special meaning.

The following table describes common POSIX BRE metacharacters:

Metacharacter	Description
.	Matches any single character. For example, a.c matches “abc”, but [a.c] matches only “a”, ”.”, or “c”
-	Used to define a range. For example, [a-c] will match characters a to c (both inclusive)
[]	Calculates and returns a value corresponding to the minimal metric in the same row from a set of values
^	Calculates and returns the maximum value
$	Calculates and returns a value corresponding to the maximum metric in the same row from a set of values
*	Calculates and returns the average value
{n}	Counts the number of rows
{n,m}	Calculates the boolean of all the boolean values in the aggregated group (returns FALSE if at least one of aggregated rows is FALSE )