If you get a memory message via the terminal during execution. For example : Allowed memory size of 134217728 bytes exhausted.
That allows you to force memory during output. You do this by using php instead of php, for example, this line php -dmemory_limit=512M
Example (indexing):
Normal: php bin/magento indexer:reindex
With memory limit: php -dmemory_limit=512M bin/magento indexer:reindex