symwatch

Watches a symlink and runs a command when the target of the symlink changes.

Installation

go get github.com/tomnomnom/symwatch

Usage

Usage:
  symwatch <symlink> <command> [<pollInterval>]

Options:
  symlink	An absolute or relative path to a symlink
  command	The command to run when the symlink target changes
  pollInterval	The number of milliseconds to wait between polling the symlink (default 500)

Notes:
  * If the symlink is unreadable for more than 5 attempts the process will exit
  * Commands are passed to `sh -c`

Exit Codes:
  0	OK
  1	Invalid Arguments
  2	Invalid Symlink
  3	Symlink Went Away

Example:
  symwatch /var/www/current 'service apache2 graceful' 500

Motivation

It's a fairly common pattern to use a symlink to point to the current version of a codebase. Sometimes it's neccesary to restart processes or clear caches when the version of a codebase changes.

Why not use inotify?

It's not portable. In particular it does not work if the symlink being polled is on an NFS share.