pv:tldr:74da6

This command is a pipeline command that consists of three parts, connected with the "|" operator.

The first part, "command1", represents the first command in the pipeline. It is the command that generates or provides input data.

The second part, "pv --size ${expected_amount_of_data_for_eta}", represents the middle command in the pipeline which uses a tool called "pv" (pipe viewer). The "--size" option is used to specify the expected amount of data that will be passed through the pipeline, and "${expected_amount_of_data_for_eta}" is a placeholder representing the actual expected amount of data (you would replace it with a real value). The purpose of using pv in this command is to show progress and estimated time of completion (ETA) as the data flows through the pipeline.

The third part, "command2", represents the final command in the pipeline. It is the command that receives the output from "command1" via the pipe and performs some further processing or action on the data.

Overall, this command allows data to flow from "command1" to "command2", while using pv to monitor the progress and estimate the time it will take for the data to complete its journey through the pipeline.