Logical Operations

User-entered logical operations are a key component of Salem's learning architecture and are referred to in the Salem nomenclature as "eval strings." These operations are created by users to inform Salem actions related to context-building workloads, alert categorization, and other logic-based evaluations.

eval strings

Definition: Eval strings are logical operations used by Salem to add and apply context to alerts based on their details. Salem can be taught to evaluate complex Boolean expressions using the and and or operators and the match() function. These expressions can be used to filter alerts, extract relevant information, and generate new context.

Basic Eval Actions

• == - Equal to operator.

• != - Not equal to operator.

• > - Greater than operator.

• < - Less than operator.

Advanced Eval Actions

bool(exp)

Evaluates to true or False

len(obj)

Returns the length of the object provided

round(num,pos)

Returns a num rounded to pos digits

coalesce(*args)

Returns the first non null value

if_then(bool,true,false)

If the bool statement evaluates to true, the value of the true case is returned, otherwise the value of the false case is returned

join(list,str)

Returns a string comprised of the list values concatenated by the value of str

match(type,match_exp,match_field)

Returns True or False based on the evaluation of the match expression.

Match types:

• in <list>: Returns true if the test is contained in the object.

• is <str>: Returns true if the test is equal to the object.

• beginsWith <str> : Returns true if the object starts with the test.

• endsWith <str>: Returns true if the object ends with the test.

• contains <str>: Returns true if the object contains the test.

• regex <str>: Returns true if the object matches the test regular expression.

• bool <str>: Returns true if the test evaluates to true.

• CIDR <str>: Returns true if the object’s IP address is within the CIDR range specified by the test.

• eval <func>: Returns true if the test evaluates to True when evaluated in the context of the object.

match('endsWith','.com',src)

now(seconds)

Returns a date object that is the current UTC time offset by the value of seconds

rex(exp,str)

returns a match value based on the regex exp evaluated over str

split(str,exp)

returns a list of str components split by the value of exp

split('10.0.0.1','.')
# returns: [10,0,0,1]

strftime(time,format)

Accepts a datetime object and a time format string. Returns a str representing time in the format provided

strptime(str,format)

Accepts a time str and format, and returns a datetime object

to_dict(json_str)

Accepts a JSON formatted string and returns an object

to_json(obj)

Accepts and object and returns a JSON formatted string

to_str(obj)

Accepts an object and returns a str formatted version of that object

url_decode(url_string)

Accepts a url quoted string and returns a unquoted version

url_encode(str)

Accepts a string and returns a url quoted version of that string

Eval Use Cases

• match actions

• webhook actions

• alert filters

• alert parsing