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    Simple Log Service:Flow control functions

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    Simple Log Service:Flow control functions

    Last Updated:May 17, 2024

    This topic describes the syntax and parameters of flow control functions. This topic also provides examples on how to use the functions.

    Functions

    Function

    Description

    e_compose

    Combines multiple operations.

    • The function is commonly used in the e_if, e_switch, or e_if_else function.

    • The function performs specified operations on a log in sequence and returns the result.

    • If the function performs an operation that deletes a log, the function no longer performs other operations on the log.

    This function can be used in combination with other functions. For more information, see Transform complex JSON data.

    e_if

    Performs an operation if a specified condition is met. You can specify multiple condition-operation pairs.

    • If a condition is met, the function performs the operation that corresponds to the condition. If the condition is not met, the function does not perform the operation, but evaluates the next condition.

    • If the function performs an operation that deletes a log, the function no longer performs other operations on the log. 

    e_if(
    e_has("a"), e_output("target-a"), 
    e_has("b"), e_output("target-b"),
)

    The preceding example of the function is equivalent to the following Python code:

    if e_has("a"):
    e_output("target-a")
if e_has("b"):
    e_output("target-b")

    This function can be used in combination with other functions. For more information, see Transform complex JSON data.

    e_if_else

    Performs an operation based on the evaluation result of a specified condition. 

    e_if_else(e_has("a"), e_output("target-a"), e_output("target-b"))

    The preceding example of the function is equivalent to the following Python code:

    if e_has("a"):
    e_output("target-a")
else:
    e_output("target-b")

    e_switch

    Performs an operation if a specified condition is met. You can specify multiple condition-operation pairs.

    • If a condition is met, the function performs the operation that corresponds to the condition and returns the result. If the condition is not met, the function does not perform the operation, but evaluates the next condition.

    • If no specified conditions are met and the default parameter is configured, the function performs the operation that is specified by the default parameter and returns the result.

    • If the function performs an operation that deletes a log, the function no longer performs other operations on the log. 

    e_switch(
    e_has("a"), e_output("target-a"), 
    e_has("b"), e_output("target-b"),
    default=e_output("target-default"), 
)

    The preceding example of the function is equivalent to the following Python code:

    if e_has("a"):
    e_output("target-a")
elif e_has("b"):
    e_output("target-b")
else:
    e_output("target-default")

    This function can be used in combination with other functions. For more information, see Distribute data to multiple destination Logstores.

    e_compose

    The e_compose function combines multiple operations.

    • Syntax

      e_compose(Operation 1, Operation 2, ...)

    • Parameters

      Parameter

      Type

      Required

      Description

      Operation 1

      Global processing function

      Yes

      A global processing function or a combination of global processing functions.

      Operation 2

      Global processing function

      No

      A global processing function or a combination of global processing functions.

    • Response

      A log on which the specified operations are performed is returned.

    • Examples

      If the value of the content field is 123, delete the age and name fields and then change the value of the content field to ctx.

      • Raw log

        content: 123
age: 23
name: twiss

      • Transformation rule

        e_if(
    e_search("content==123"),
    e_compose(e_drop_fields("age|name"), e_rename("content", "ctx")),
)

      • Result

        ctx: 123

    • References

      This function can be used in combination with other functions. For more information, see Transform complex JSON data.

    e_if

    The e_if function performs an operation if a specified condition is met.

    • Syntax

      e_if(Condition, Operation)
e_if(Condition 1, Operation 1, Condition 2, Operation 2, ...)
      Note

      You must specify the Condition and Operation parameters in pairs.

    • Parameters

      Parameter

      Type

      Required

      Description

      Condition

      Arbitrary

      Yes

      An expression or a combination of expressions. If the result is not a Boolean value, the system evaluates whether the condition is true or false.

      Operation

      Global processing function

      Yes

      A global processing function or a combination of global processing functions.

    • Response

      A log on which the specified operations are performed is returned.

    • Examples

      • Example 1: Match a field value against specified values and perform an operation.

        If the value of the result field is failed or failure, set the __topic__ field to login_failed_event. 

        e_if(e_match("result", r"failed|failure"), e_set("__topic__", "login_failed_event"))

      • Example 2: Perform evaluation based on a field value and perform an operation.

        If the request_body field exists and the field is not empty, call the field processing function e_json to expand the value of the request_body field into multiple values. 

        e_if(v("request_body"), e_json("request_body"))

      • Example 3: Perform advanced evaluation and perform an operation.

        If the value of the valid field is failed in lowercase, discard the log. 

        e_if(op_eq(str_lower(v("valid")), "failed"), DROP)

      • Example 4: Perform multiple operations in sequence based on specified conditions. 

        e_if(True, e_set("__topic__", "default_login"), 
     e_match("valid", "failed"), e_set("__topic__", "login_failed_event")
  )

    • References

      This function can be used in combination with other functions. For more information, see Transform complex JSON data.

    e_if_else

    The e_if_else function performs an operation based on the evaluation result of a specified condition.

    • Syntax

      e_if_else(Condition, Operation 1 if Condition evaluates to true, Operation 2 if Condition evaluates to false)

    • Parameters

      Parameter

      Type

      Required

      Description

      Condition

      Arbitrary

      Yes

      An expression or a combination of expressions. If the result is not a Boolean value, the system evaluates whether the condition is true or false.

      Operation 1 if Condition evaluates to true

      Global processing function

      Yes

      A global processing function or a combination of global processing functions.

      Operation 2 if Condition evaluates to false

      Global processing function

      Yes

      A global processing function or a combination of global processing functions.

    • Response

      A log on which an operation is performed based on the evaluation result of the specified condition is returned.

    • Examples

      If the value of the result field is ok or pass or if the value of the status field is 200, retain the log.

      • Raw log

        result: ok
status: 400
        result: Pass
status: 200
        result: failure
status: 500

      • Transformation rule

        e_if_else(
    op_or(e_match("result", r"(?i)ok|pass"), e_search("status== 200")), KEEP, DROP
)

      • Result: The first two logs are retained. The third log is discarded. 

        result: ok
status: 400
        result: Pass
status: 200

    e_switch

    The e_switch function performs an operation if a specified condition is met.

    • Syntax

      e_switch(Condition 1, Operation 1, ..., default=None)
      Note

      You must specify the Condition and Operation parameters in pairs.

    • Parameters

      Parameter

      Type

      Required

      Description

      Condition

      Arbitrary

      Yes

      An expression or a combination of expressions. If the result is not a Boolean value, the system evaluates whether the condition is true or false.

      Operation

      Global processing function

      Yes

      A global processing function or a combination of global processing functions.

      default

      Global processing function

      No

      A global processing function or a combination of global processing functions. If no specified conditions are met, the operation specified by the default parameter is performed.

    • Response

      A log on which the specified operations are performed is returned.

    • Examples

      • If the value of the content field is 123, set the __topic__ field to Number. If the value of the data field is 123, set the __topic__ field to PRO.

        • Raw log

          __topic__:  
age: 18
content: 123
name: maki
data: 342
          __topic__:  
age: 18
content: 23
name: maki
data: 123

        • Transformation rule

          e_switch(
    e_search("content==123"),
    e_set("__topic__", "Number", mode="overwrite"),
    e_search("data==123"),
    e_set("__topic__", "PRO", mode="overwrite"),
)

        • Result

          __topic__: Number
age: 18
content: 123
name: maki
data: 342
          __topic__: PRO
age: 18
content: 23
name: maki
data: 123

      • You can combine the e_switch and e_output functions to ship the logs that meet specified conditions to different Logstores. If you specify default=e_drop(), the logs that do not meet specified conditions are discarded and not shipped. If you do not configure the default parameter, the logs that do not meet specified conditions are shipped to the first Logstore that you specify.

        • Raw log

          __topic__: sas-log-dns
test: aliyun

__topic__: aegis-log-network
test:ecs

__topic__: local-dns
test:sls

__topic__: aegis-log-login
test: sls

        • Transformation rule

          e_switch(e_match("__topic__","sas-log-dns"),e_output(name="target1"),
e_match("__topic__","sas-log-process"),e_output(name="target2"),
e_match("__topic__","local-dns"),e_output(name="target3"),
e_match("__topic__","aegis-log-network"),e_output(name="target4"),
e_match("__topic__","aegis-log-login"),e_output(name="target5"),
default=e_drop())

    • References

      This function can be used in combination with other functions. For more information, see Distribute data to multiple destination Logstores.