Man Pages

ausearch-expression(5) - phpMan ausearch-expression(5) - phpMan

Command: man perldoc info search(apropos)  


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


       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  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
       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)