Appendix: Regular Expressions

In This Section:

Regular Expression Syntax

This table shows the Check Point implementation of standard regular expression metacharacters.

Metacharacter	Name	Description
\	Backslash	escape metacharacters non-printable characters character types
[ ]	Square Brackets	character class definition
( )	Parenthesis	sub-pattern, to use metacharacters on the enclosed string
{min[,max]}	Curly Brackets	min/max quantifier {n} - exactly n occurrences {n,m} - from n to m occurrences {n,} - at least n occurrences
.	Dot	match any character
?	Question Mark	zero or one occurrences (equals {0,1})
*	Asterisk	zero or more occurrences of preceding character
+	Plus Sign	one or more occurrences (equals {1,})
\|	Vertical Bar	alternative
^	Circumflex	anchor pattern to beginning of buffer (usually a word)
$	Dollar	anchor pattern to end of buffer (usually a word)
-	hyphen	range in character class

To use non-printable characters in patterns, escape the reserved character set.

Character	Description
\a	alarm; the BEL character (hex code `07`)
\cX	"control-X", where X is any character
\e	escape (hex code `1B`)
\f	formfeed (hex code `0C`)
\n	newline (hex code `0A`)
\r	carriage return (hex code `0D`)
\t	tab (hex code `09`)
\ddd	character with octal code `ddd`
\xhh	character with hex code `hh`

To specify types of characters in patterns, escape the reserved character.

Character	Description
\d	any decimal digit [0-9]
\D	any character that is not a decimal digit
\s	any whitespace character
\S	any character that is not whitespace
\w	any word character (underscore or alphanumeric character)
\W	any non-word character (not underscore or alphanumeric)

Select URLs are defined as Regular Expression only if the application or site URL is entered as a regular expression using the correct syntax.

The meaning of the asterisk ( * ) depends on its use.

In regular expressions, the asterisk is a metacharacter for zero or more instances of the preceding character.
Without regular expressions, the asterisk is a wildcard, for zero or more instances of any character.

For example, to block a domain that ends with "example.com" (such as www.example.com):

Regular Expression	`.*\.example\.com`
Wildcard	`*.example.com`	Important! If you use this string as a regular expression, policy install fails. The gateway cannot resolve the regular expression to a URL, because there is no preceding character to find.

More examples of regular expressions:

To match subdomains of mydomain.com: (^|.*\.)mydomain\.com

To match domain and subdomains of mydomain.com: (^|.*\.)*mydomain\.com