How to set a Spring Boot property with an underscore in its name via Environment Variables?

This is an old question but I'll answer it in case somebody else (like me) ends up here looking for this information.

HIBERNATE_FORMAT_SQL should do the trick

Actually it is not the OS environment variable that is "translated" but rather the Spring property name that is.

The name is translated in several ways and looked up against available environment variables. E.g. "hibernate.format.sql" is looked up as:

1. hibernate.format.sql (as is)
2. hibernate_format_sql (dots replaced with underscores)
3. hibernate_format_sql (dashes replaced with underscores, the same in your case)
4. hibernate_format_sql (dashes & dots replaced with underscores, the same in your case)

Then the same with UPPERCASE:

5. HIBERNATE.FORMAT.SQL (as is)
6. HIBERNATE_FORMAT_SQL (dots replaced with underscores)
7. HIBERNATE_FORMAT_SQL (dashes replaced with underscores, the same again)
8. HIBERNATE_FORMAT_SQL (dashes & dots replaced with underscores, the same again)

Although you cannot set an environment variable with a dot in the name with the set or export commands it is however possible with the env command. I defer judgement whether this is a good idea or not:

env "my.dotted.name=\"a value\"" the-command-you-want-to-run

Have a look at SystemEnvironmentPropertySource.java for details. I link to a specific version but you should make sure to look at the version you are using.

To troubleshoot these kinds of problems in a production environment you could try turning on debug logging for the property resolving code:

logging:
  level:
    org.springframework.core.env: DEBUG

... or by setting the appropriate environment variable :)

Edit: I highly recommend being familiar with the relevant Spring Boot documentation topic: https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-external-config

For the more tricky examples in the comments here, e.g. spring.jpa.properties.hibernate.criteria.literal_handling_mode, there might be different solutions available depending on how you launch you application.

You could set the variable as JSON, embedded in an environment variable.

env SPRING_APPLICATION_JSON='{"spring":{"jpa":{"properties":{"hibernate":{"criteria":{"literal_handling_mode":"BIND"}}}}}}' ./gradlew bootRun

Simply setting the variable as is might work also:

env spring.jpa.properties.hibernate.criteria.literal_handling_mode=BIND ./gradlew bootRun

Both of the above worked in my setup in so far as I was able to get the value in the running Spring Boot application this way:

@Value("${spring.jpa.properties.hibernate.criteria.literal_handling_mode}")
private String testSettingThroughEnvVariable;

Hope this helps! YMMV