rerun a build or test command automatically when watched files change using entr instead of polling with inotifywait
domain: eradman.com · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Feed entr a list of file paths on stdin (typically from ls or find) plus the command to run: `ls *.c | entr make`, which re-executes the command whenever any listed file changes.
Restart a long-running process on change (rather than a one-shot command) using -r, which sends SIGTERM to the previous instance's own process group before starting a new one.
Track directories rather than only files, and exit if a new matching file is added, using -d.
Clear the terminal before each rerun for cleaner output using -c.
Use -s to run the command through the shell named in $SHELL, with /_ substituted for the path of the file that triggered the event, when the command needs to know which file changed.
Known gotchas
entr does not watch for new files added to a directory by default; the file list is fixed at startup, so newly created files won't trigger reruns unless -d is used and the file list is re-piped.
-r creates a process group specifically so scripts under it can't mask the SIGTERM used to stop the previous run; commands that trap or ignore SIGTERM in a way that escapes the process group may not restart cleanly.
entr relies on kqueue/inotify to avoid polling, so watching files over network filesystems that don't fully support these notification mechanisms can silently degrade to missed or delayed events.
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