A lightweight utility that executes commands whenever your files change, using efficient system-level monitoring instead of polling. Built with kqueue(2) on BSD/Mac and inotify(7) on Linux, entr delivers instant feedback for developers working on the command line.

Key capabilities:

Automatically rebuild projects when source files are modified
Auto-reload development servers with the -r flag
Clear screen and re-run commands with -c option
Restart processes on file changes using -z flag
Limit output and chain commands for cleaner workflows
Works across BSD, Mac OS, Linux, Docker, and WSL environments

Common use cases include rebuilding projects with live output limiting, launching auto-reloading Node.js servers, re-executing database queries when SQL scripts update, and monitoring directories for new or modified files. The tool integrates seamlessly into development workflows, eliminating manual re-runs and accelerating the edit-test cycle. Perfect for test runners, build systems, and any development process requiring immediate feedback on file changes.