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

       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.

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 any value is false.

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

AUTHOR

       Miloslav Trmac