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
\regexp 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 followed 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
string. If field is not present or does not define an "interpreted" string, the result of the compari‐
son 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 vir‐
tual 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 \regexp regexp-or-string, the current audit record is taken as a string (without inter‐
preting field values), and matched against regexp-or-string. regexp-or-string is an extended regular expres‐
sion, 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 evaluation 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:
\timestamp
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.
\record_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
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