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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 _  sym-
              bol.

       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 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_inter-
              pret_field(3).  Each virtual field may define  an  "interpreted"
              string.   If  field is not present or does not define an "inter-
              preted" string, the result of the comparison is  false  (regard-
              less 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 reg-
       ular expression, using a string or regexp token (in other words, delim-
       ited 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 evalua-
       tion 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 be
              formatted as:
                   ts:seconds.milli
              where seconds and milli are decimal numbers specifying the  sec-
              onds and milliseconds part of the timestamp, respectively.

       \timestamp_ex
              This  is  similar  to  \timestamp  but also includes the event's
              serial number.  value must be formatted as:
                   ts:seconds.milli:serial
              where serial is a decimal number specifying the  event's  serial
              number.

       \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

Red Hat                            Feb 2008             AUSEARCH-EXPRESSION(5)