bionic (5) ausearch-expression.5.gz

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