pv

pv is a Unix pipeline utility for monitoring and shaping data as it moves between commands or files. It adds progress, rate, ETA, and transfer controls without changing the rest of the pipeline.

• Show progress, throughput, bytes transferred, and ETA for long-running copy, compression, backup, disk-image, or log-processing pipelines.
• Throttle or reshape transfers with rate limits, buffer sizing, store-and-forward, sparse output, discard mode, and read-error skipping for bulk data moves.
• Watch file descriptors opened by another process, or query and retune a running pv instance with --watchfd, --query, and --remote.

• Fits shell loops well because it sits inline in existing pipelines and exposes direct flags for inspect and control instead of an interactive UI.
• Machine-readable output exists, but only through --numeric and custom --format strings; default progress output is human-oriented text on stderr.
• Best as a support primitive around data-moving commands such as tar, dd, gzip, or custom producers and consumers, not as a standalone service-control CLI.

• --watchfd is documented for Linux and macOS only.
• --remote and --query require writable IPC paths such as /run/user/<uid>/ or $HOME/.pv/.