Options of regular expressions

This chapter lists regular expressions supported by AxoSyslog and their available supported type() and flags() options.

By default, AxoSyslog uses PCRE-style regular expressions. To use other expression types, add the type() option after the regular expression.

The AxoSyslog application supports the following regular expression type() options:

• Perl Compatible Regular Expressions (pcre)
• Literal string searches (string)
• Glob patterns without regular expression support (glob)

By default, AxoSyslog uses PCRE-style regular expressions, which are supported on every platform starting with AxoSyslog version 3.1. To use other expression types, add the type() option after the regular expression.

Perl Compatible Regular Expressions (pcre)

Description: Uses Perl Compatible Regular Expressions (PCRE). If the type() parameter is not specified, AxoSyslog uses PCRE regular expressions by default.

PCRE flags

PCRE-style regular expressions have the following flags() options:

• disable-jit: Switches off the just-in-time compilation function for PCRE regular expressions.

• dupnames: Allows using duplicate names for named subpatterns. Configuration example:

  filter { match("(?<DN>foo)|(?<DN>bar)" value(MSG) flags(store-matches, dupnames)); };
  ...
  destination { file(/dev/stdout template("$DN\n")); };
  

• global: Usable only in rewrite rules, flags("global") matches for every occurrence of the expression, not only the first one.

• ignore-case: Disables case-sensitivity.

• newline:

  When configured, it changes the newline definition used in PCRE regular expressions to accept either of the following:

  • a single carriage-return
  • linefeed
  • the sequence carriage-return and linefeed (\\r, \\n and \\r\\n, respectively)

  This newline definition is used when the circumflex and dollar patterns (^ and $) are matched against an input. By default, PCRE interprets the linefeed character as indicating the end of a line. It does not affect the \\r, \\n or \\R characters used in patterns.

• store-matches: Stores the matches of the regular expression into the $0, ... $255 variables. The $0 stores the entire match, $1 is the first group of the match (parentheses), and so on. Named matches (also called named subpatterns), for example, (?<name>...), are stored as well. Matches from the last filter expression can be referenced in regular expressions.

  Note To convert match variables into a AxoSyslog list, use the $* macro, which can be further manipulated using List manipulation, or turned into a list in type-aware destinations.

• unicode:

  Use Unicode support for UTF-8 matches: UTF-8 character sequences are handled as single characters.

• utf8: An alias for the unicode flag.

Literal string searches (string)

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.

String search flags

Literal string searches have the following flags() options:

• global: Usable only in rewrite rules, flags("global") matches for every occurrence of the expression, not only the first one.

• ignore-case: Disables case-sensitivity.

• prefix: During the matching process, patterns (also called search expressions) are matched against the input string starting from the beginning of the input string, and the input string is matched only for the maximum character length of the pattern. The initial characters of the pattern and the input string must be identical in the exact same order, and the pattern’s length is definitive for the matching process (that is, if the pattern is longer than the input string, the match will fail).

• store-matches: Stores the matches of the regular expression into the $0, ... $255 variables. The $0 stores the entire match, $1 is the first group of the match (parentheses), and so on. Named matches (also called named subpatterns), for example, (?<name>...), are stored as well. Matches from the last filter expression can be referenced in regular expressions.

  Note To convert match variables into a AxoSyslog list, use the $* macro, which can be further manipulated using List manipulation, or turned into a list in type-aware destinations.

• substring: The given literal string will match when the pattern is found within the input. Unlike flags("prefix"), the pattern does not have to be identical with the given literal string.

Glob patterns without regular expression support (glob)

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.

Glob patterns don’t support any flags.