logbackspring-logback

What is the meaning of colon dash ":-" on spring logback pattern layout configuration?


and how it differs from just a colon?

Example

<property name="CONSOLE_LOG_PATTERN" value="${CONSOLE_LOG_PATTERN:-%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}}"/>

Citing references would be much appreciated. Thank you.


Solution

  • As mentioned in the documentation

    Under certain circumstances, it may be desirable for a variable to have a default value if it is not declared or its value is null. As in the Bash shell, default values can be specified using the ":-" operator. For example, assuming the variable named aName is not defined, "${aName:-golden}" will be interpreted as "golden".