Symantec™ Security Gateways Reference Guide - Sawmill

Controlling service accessContent filtering73Table 5-1SymbolSupported regular expression symbols (Continued)Description- Specifies a range of characters in a set. If you wish to make this character one of the matchablecharacters in a set, it must be used in a context where it cannot possibly indicate a range. Thiscan either be at the beginning of the set, or immediately after a range.^Beginning anchor character and matches the blank space at the beginning of a line. It must beplaced before the pattern that you want to match. It matches if that pattern appears at thebeginning of the line.$ End anchor character and matches the blank space at the end of a line. You must place itimmediately after the pattern that you are looking to match. It matches if that pattern appears atthe end of the line.| This is the Boolean OR character and requires two patterns, one preceding the | and onefollowing it. It matches either the preceding pattern or the following pattern./ Requires two patterns, one preceding the / and one following it. This character says to match thepreceding pattern only if it is followed by the second pattern.“...” Tells the parser to interpret literally everything inside of the “ ”.() Used to group a series of regular expressions to form a new, single expression.{} Used to specify exactly how many occurrences of the preceding pattern should be matched. Ifjust a single number is type (such as {2}), the number of occurrences of the pattern must matchexactly (2 times in this case). If a comma is used (such as {1,3}), it specifies an upper and lowerbound, with the pattern occurring at least as many occurrences as the first number, but no morethan the second number. Leaving off the first number designates no minimum occurrence forthe pattern, and leaving off the last number designates no maximum occurrence.\b Matches a word boundary.\B Matches a non-word boundary.\n Matches a newline character.\w Matches any alphanumeric character, including the underscore (same as [A-Za-z0-9_]).\W Matches any non-word character (same as [^A-Za-z0-9_]).\< Anchors the pattern to the beginning of a word.\> Anchors the pattern to the end of a word.‘ Marks the beginning of a buffer.\’ You must use this character combination to terminate a buffer. If a single quote is used again,everything in between the two single quotes is interpreted literally.For example, let’s say that you want to prevent employees from browsing Web sites with adult material.One common combination of letters to see in a adult Web site URL might be “xxx.” To restrict URLs withthis three letter combination, you could put together an expression that looks likexxxThis expression tells the security gateway to look for the combination of three lowercase xs in a URL, and iffound, deny the request. This rather simplistic expression is fine if the URL does not use uppercase letters,and if the URL has a minimum of 3 xs in it.It may be impossible to match the patterns of all sites you want to exclude with one expression, so it iscommon to add additional expressions. For example,XXX