Snort - the de facto standard for intrusion detection/prevention
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Format

pcre:[!]"(/<regex>/|m<delim><regex><delim>)[ismxAEGRUB]";
The post-re modifiers set compile time flags for the regular expression.

Table: Perl compatible modifiers
i case insensitive
s include newlines in the dot metacharacter
m By default, the string is treated as one big line of characters. ^ and $ match at the beginning and ending of the string. When m is set, ^ and $ match immediately following or immediately before any newline in the buffer, as well as the very start and very end of the buffer.
x whitespace data characters in the pattern are ignored except when escaped or inside a character class

Table: PCRE compatible modifiers
A the pattern must match only at the start of the buffer (same as ^ )
E Set $ to match only at the end of the subject string. Without E, $ also matches immediately before the final character if it is a newline (but not before any other newlines).
G Inverts the "greediness" of the quantifiers so that they are not greedy by default, but become greedy if followed by "?".

Table: Snort specific modifiers
R Match relative to the end of the last pattern match. (Similar to distance:0;)
U Match the decoded URI buffers (Similar to uricontent)
B Do not use the decoded buffers (Similar to rawbytes)

The modifiers R and B should not be used together.


next up previous contents
Next: Example Up: pcre Previous: pcre   Contents
Steven Sturges 2006-12-08