AUSEARCH-EXPRESSION(5)						    Linux Audit 					    AUSEARCH-EXPRESSION(5)

NAME

       ausearch-expression - audit search expression format

OVERVIEW

       This man page describes the format of "ausearch expressions".  Parsing and evaluation of these expressions is provided by libauparse and is
       common to applications that use this library.

LEXICAL STRUCTURE

       White space (ASCII space, tab and new-line characters) between tokens is ignored.  The following tokens are recognized:

       Punctuation
	      ( ) 

       Logical operators
	      ! && ||

       Comparison operators
	      < <= == > >= !== i= i!= r= r!=

       Unquoted strings
	      Any non-empty sequence of ASCII letters, digits, and the _ symbol.

       Quoted strings
	      A sequence of characters surrounded by the " quotes.  The  character starts an escape sequence.	The only defined escape  sequences
	      are \ and ".  The semantics of other escape sequences is undefined.

       Regexps
	      A  sequence  of  characters  surrounded  by  the	/ characters.  The  character starts an escape sequence.  The only defined escape
	      sequences are \ and /.	The semantics of other escape sequences is undefined.

       Anywhere an unquoted string is valid, a quoted string is valid as well, and vice versa.	In particular, field names may be specified  using
       quoted strings, and field values may be specified using unquoted strings.

EXPRESSION SYNTAX

       The primary expression has one of the following forms:

	      field comparison-operator value

	      
egexp string-or-regexp

       field  is  either  a string, which specifies the first field with that name within the current audit record, or the  escape character fol-
       lowed by a string, which specifies a virtual field with the specified name (virtual fields are defined in a later section).

       field is a string.  operator specifies the comparison to perform

       r= r!= Get the "raw" string of field, and compare it to value.  For fields in audit records, the "raw" string is the exact string stored in
	      the  audit  record  (with  all escaping and unprintable character encoding left alone); applications can read the "raw" string using
	      auparse_get_field_str(3).  Each virtual field may define a "raw" string.	If field is not present or does not define a "raw" string,
	      the result of the comparison is false (regardless of the operator).

       i= i!= Get  the "interpreted" string of field, and compare it to value.	For fields in audit records, the "interpreted" string is an "user-
	      readable" interpretation of the field value; applications can read the "interpreted" string using auparse_interpret_field(3).   Each
	      virtual field may define an "interpreted" string.  If field is not present or does not define an "interpreted" string, the result of
	      the comparison is false (regardless of the operator).

       < <= == > >= !==
	      Evaluate the "value" of field, and compare it to value.  A "value" may be defined for any field or virtual field, but no "value"	is
	      currently  defined  for  any audit record field.	The rules of parsing value for comparing it with the "value" of field are specific
	      for each field.  If field is not present, the result of the comparison is false (regardless of the operator).   If  field  does  not
	      define a "value", an error is reported when parsing the expression.

       In  the	special  case  of 
egexp regexp-or-string, the current audit record is taken as a string (without interpreting field values), and
       matched against regexp-or-string.  regexp-or-string is an extended regular expression, using a string or  regexp  token	(in  other  words,
       delimited by " or /).

       If E1 and E2 are valid expressions, then !  E1, E1 && E2, and E1 || E2 are valid expressions as well, with the usual C semantics and evalu-
       ation priorities.  Note that !  field op value is interpreted as !(field op value), not as (!field) op value.

VIRTUAL FIELDS

       The following virtual fields are defined:

       	imestamp
	      The value is the timestamp of the current event.	value must have the ts:seconds.milli format, where seconds and milli  are  decimal
	      numbers specifying the seconds and milliseconds part of the timestamp, respectively.

       
ecord_type
	      The value is the type of the current record.  value is either the record type name, or a decimal number specifying the type.

SEMANTICS

       The expression as a whole applies to a single record.  The expression is true for a specified event if it is true for any record associated
       with the event.

EXAMPLES

       As a demonstration of the semantics of handling missing fields, the following expression is true if field is present:

	      (field r= "") || (field r!= "")

       and the same expression surrounded by !( and ) is true if field is not present.

FUTURE DIRECTIONS

       New escape sequences for quoted strings may be defined.

       For currently defined virtual fields that do not define a "raw" or "interpreted" string, the definition may  be	added.	 Therefore,  don't
       rely on the fact that comparing the "raw" or "interpreted" string of the field with any value is false.

       New formats of value constants for the 	imestamp virtual field may be added.

AUTHOR

       Miloslav Trmac

Red Hat 							     Feb 2008						    AUSEARCH-EXPRESSION(5)