Monitoring File System Updates by VIM in Python

May 13, 2013

Due to the way VIM updates files event-based kernel hooks for file system updates are not triggered when a file is updated. This makes triggering automated build scripts tricky as the preferred method of file system monitoring does not work.

But it is still possible to monitor file system updates in VIM. Unix file systems (including those used on OS X and most Linux distros) track the last time a file was modified, a field which is updated when VIM saves.

In Python this information can be read using the standard library’s os.path.getmtime() method. Combined with a simple polling mechanism, it’s easy to monitor and trigger events based on file system updates by VIM.

For an example of this in action see my build-monitory.py script which is part of a build-assets repository on github. The build-monitor.py file uses polling to trigger Ant / Buildr scripts for tasks like compiling LESS, minifying CSS, and combining JavaScript files.

VIM is an Edge Case

The fact that VIM does not trigger a file change event is an edge case. Polling solutions are never ideal, requiring a compromise between resource use (short poll times) and latency after event (long poll times).

Whenever possible, using event-based file system monitoring is preferred. Each operating system has some system for event-based file system monitoring.

For cross-platform file system monitoring in Python Watchdog is highly recommended. Watchdog simplifies the varied APIs and obscurs platform specific idiosyncrasies involved in file system monitoring.