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NAME | OVERVIEW | LEXICAL STRUCTURE | EXPRESSION SYNTAX | VIRTUAL FIELDS | SEMANTICS | EXAMPLES | FUTURE DIRECTIONS | AUTHOR | COLOPHON |
AUSEARCH-EXPRESSION(5) Linux Audit AUSEARCH-EXPRESSION(5)
ausearch-expression - audit search expression format
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.
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.
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
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 \regexp 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
evaluation priorities. Note that ! field op value is interpreted as
!(field op value), not as (!field) op value.
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.
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.
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.
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 \timestamp virtual field may
be added.
Miloslav Trmac
This page is part of the audit (Linux Audit) project. Information
about the project can be found at
⟨http://people.redhat.com/sgrubb/audit/⟩. If you have a bug report
for this manual page, send it to linux-audit@redhat.com. This page
was obtained from the project's upstream Git repository
⟨https://github.com/linux-audit/audit-userspace.git⟩ on 2017-07-05.
If you discover any rendering problems in this HTML version of the
page, or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
Red Hat Feb 2008 AUSEARCH-EXPRESSION(5)
Pages that refer to this page: ausearch_add_expression(3), ausearch_add_interpreted_item(3), ausearch_add_item(3), ausearch_add_timestamp_item(3), ausearch_add_timestamp_item_ex(3)