This message was deleted.

3. a new task that extracts the specific line from the file and puts it in a temporary file, then configure your original task to use that temporary file as input

Great idea!

by the way, it is possible for your task to handle this internally: https://docs.gradle.org/current/userguide/custom_tasks.html#sec:storing_incremental_task_state but unless you have specific needs otherwise, I think using a pre-processing task is easier