Filters and substitution rewrite rules can use regular expressions. In regular expressions, the characters ()[].*?+^$|\ are used as special symbols. Depending on how you want to use these characters and which quotation mark you use, these characters must be used differently, as summarized below.
Strings between single quotes ('string') are treated literally and are not interpreted at all, you do not have to escape special characters. For example, the output of '\x41' is \x41 (characters as follows: backslash, x(letter), 4(number), 1(number)). This makes writing and reading regular expressions much more simple: it is recommended to use single quotes when writing regular expressions.
When enclosing strings between double-quotes ("string"), the string is interpreted and you have to escape special characters, that is, to precede them with a backslash (\) character if they are meant literally. for example, the output of the "\x41" is simply the letter a. Therefore special characters like \(backslash) or "(quotation mark) must be escaped (\\ and \"). The following expressions are interpreted: \a, \n, \r, \t, \v. For example, the \$40 expression matches the $40 string. Backslashes have to be escaped as well if they are meant literally, for example, the \\d expression matches the \d string.
TIP: If you use single quotes, you do not need to escape the backslash, for example, match("\\.") is equivalent to match('\.').
Enclosing alphanumeric strings between double-quotes ("string") is not necessary, you can just omit the double-quotes. for example, when writing filters, match("sometext") and match(sometext) will both match for the sometext string.
NOTE: Only strings containing alphanumerical characters can be used without quotes or double quotes. If the string contains whitespace or any special characters (()[].*?+^$|\ or ;:#), you must use quotes or double quotes.
When using the ;:# characters, you must use quotes or double quotes, but escaping them is not required.
By default, all regular expressions are case sensitive. To disable the case sensitivity of the expression, add the flags(ignore-case) option to the regular expression.
filter demo_regexp_insensitive {
host("system" flags(ignore-case));
};
NOTE:Adding the flags(ignore-case) option to glob patterns does not disable case sensitivity.
The regular expressions can use up to 255 regexp matches (${1} ... ${255}), but only from the last filter and only if the flags("store-matches") flag was set for the filter. For case-insensitive searches, use the flags("ignore-case") option.
This chapter lists regular expressions supported by syslog-ng Open Source Edition (syslog-ng OSE) and their available supported type() and flags() options.
By default, syslog-ng OSE uses PCRE-style regular expressions. To use other expression types, add the type() option after the regular expression.
The syslog-ng OSE application supports the following regular expression type() options:
By default, syslog-ng OSE uses PCRE-style regular expressions, which are supported on every platform starting with syslog-ng OSE version 3.1. To use other expression types, add the type() option after the regular expression.
The syslog-ng OSE application supports the following type() options:
Description: Uses Perl Compatible Regular Expressions (PCRE). If the type() parameter is not specified, syslog-ng OSE uses PCRE regular expressions by default.
For more information about the flags() options of PCRE regular expressions, see The flags() options of regular expressions.
Description: Matches the strings literally, without regular expression support. By default, only identical strings are matched. For partial matches, use the flags("prefix") or the flags("substring") flags.
For more information about the flags() options of literal string searches, see The flags() options of regular expressions.
Description: Matches the strings against a pattern containing * and ? wildcards, without regular expression and character range support. The advantage of glob patterns to regular expressions is that globs can be processed much faster.
*: matches an arbitrary string, including an empty string
?: matches an arbitrary character
The wildcards can match the / character.
You cannot use the * and ? literally in the pattern.
Similarly to the type() options, the flags() options are also optional within regular expressions.
The following list describes each type() option's flags() options.
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