entr

Run command when file changes

$ ls [*.py] | entr [python test.py]

$ ls [*.md] | entr -c [make html]

$ ls [main.go] | entr -r [go run main.go]

$ ls [config.yml] | entr -p [./deploy.sh]

$ ls [*.js] | entr -s '[eslint /_]'

entr [options] command [args...]

entr runs commands when files change. It watches files listed on stdin and executes the specified command whenever any change is detected.
The tool is ideal for development workflows: rerunning tests, rebuilding projects, or restarting servers on source changes. The -r flag handles processes that need restart rather than re-execution.
entr uses efficient kernel file notification mechanisms (kqueue, inotify) rather than polling.

COMMAND

Command to run when files change.

Clear screen before running.

Restart persistent process.

Postpone first execution.

Execute with shell.

Track directories for new files.

Exit on process completion.

Placeholder for changed file.

File list is fixed at startup (use -d for new files). stdin must list files. Some editors may not trigger events properly. Maximum file count limited by system.

entr was created by Eric Radman as a simple, Unix-philosophy tool for file watching. It focuses on doing one thing well: running commands when files change.

inotifywait(1), watchexec(1), fswatch(1)