watcherp

watcherp will watch for port binding changes (ports started or stopped binding on a network addresss) and will execute specified commands or shell scripts (-a, -d) depending on the event. Once all events have happened during one round (-i), a trigger command can be executed (-t). Note, the trigger command will only be execute when at least one add or delete command has succeeded with exit code 0.

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If you need the same functionality to monitor file system changes, check out watcherd.

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Modes

watcherp can either use netstat or ss to watch for binding port changes. The default is to use netstat.

Placeholders

There are two placeholders available that make it easier to use custom commands/scripts for the add (-a) or delete (-d) action.:

• %p Port that started or stopped binding
• %n The network address the port started or stopped binding to

You can specify the placeholders as many times as you want. See the following example section for usage.

Examples

By using vhost_gen.py (which is capable of creating Nginx or Apache vhost config files for normal vhosts or reverse proxies), the following example will create new Nginx reverse proxy vhosts on-the-fly. watcherp uses its add command to parse network address and port to vhost_gen.py which will create a configuration file and reloads Nginx.

# %n will be replaced by watcherp with the network address the port started binding to
# %p will be replaced by watcherd with the port that started binding
# -p 80 Ignores the web server port itself.
watcherp -v \
  -p 80 \
  -a "vhost_gen.py -r 'http://%n:%p' -l / -n 'proxy-%p.example.com' -s" \
  -d "rm /etc/nginx/conf.d/proxy-%p.example.com.conf" \
  -t "nginx -s reload"

Usage

Usage: watcherp -a <cmd> -d <cmd> [-p <ports> -t <cmd> -w <str> -i <int> -v]
       watcherp --help
       watcherp --version

watcherp will look for port binding changess (added and removed port bindings)
and will execute specified commands or shell scripts (-a, -d) depending on the event.
Once all events have happened during one round (-i), a trigger command can be executed (-t).
Note, the trigger command will only be execute when at least one add or delete command has succeeded with exit code 0.

Required arguments:
  -a <cmd>      Command to execute when a port started to bind on an address.
                You can also append the following placeholders to your command string:
                %p The port that started binding.
                %n The network address the port binded on.
                Example: -a "script.sh -f %p -c %n -a %p"
  -d <cmd>      Command to execute when a binding port was removed from an address.
                You can also append the following placeholders to your command string:
                %p The port that started binding.
                %n The network address the port binded on.
                Example: -b "script.sh -f %p -c %n -a %p"

Optional arguments:
  -p <ports>    Comma separated list of ports to ignore.
  -t <cmd>      Command to execute after all binding ports have been added or removed during one round.
                No argument will be appended.
  -w <str>      The port binding watcher to use. Valid values are:
                'netstat': Uses netstat binary to watch for binding changes.
                'ss':      Uses ss binary to watch for binding changes.
                The default is to use 'netstat' as the watcher.
  -i <int>      Specify the interval in seconds for how often to look for port changes.
  -v            Verbose output.

Misc arguments:
  --help        Show this help screen.
  --version     Show version information.