syslog-ng Open Source Edition 3.30 - Administration Guide

Regular expressions

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));
};

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.

Options of regular expressions

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:

• Perl Compatible Regular Expressions (pcre)

• Literal string searches (string)

• Glob patterns without regular expression support (glob)

The type() options of regular expressions

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:

The flags() options of regular expressions

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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