A regular expression is a formalism used to specify a set of strings with a single expression. Since the implementation of regular expressions comes from the Java standard library, the syntax of expressions is the same as in Java: see http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html.
Example 66.27. Regular Expressions Examples
means the string has to be exactly five characters long and it can only contain the
this example expression matches any string which starts with a character
^ sign means exception;
a-d means characters from
these characters can be followed by
zero or more (
*) other characters;
the dot stands for an arbitrary character.
For more detailed explanation of how to use regular expressions, see the
Java documentation for
The meaning of regular expressions can be modified using embedded flag expressions. The expressions include the following:
.matches any character, including line terminators.
$to express the beginning and end of the line, respectively (this includes at the beginning and end of the entire expression).
Further reading and description of other flags can be found at http://docs.oracle.com/javase/tutorial/essential/regex/pattern.html.