Erwatch

Erwatch is an Erlang/OTP application for tracking changes in a file system. It doesn't have any dependency other than a recent version of Erlang/OTP (17+ should be OK) and optionally rebar3. It is only tested on Linux/OSX, but only Erlang/OTP standard library functions are used, so it should work on any platform where Erlang/OTP runs.

Install

Erwatch uses rebar3 to build and tests and it is available on hex.pm. Just include the following in your rebar.config:

{deps, [erwatch]}.

Since Erwatch is an OTP application, it must be started before using. You can do that by including erwatch in your *.app.src or *.app file, like:

...
  {applications,
   [kernel,
    stdlib,
    erwatch
   ]},
...

rebar3 has a nice way of starting apps in the shell, you can try:

$ rebar3 shell --apps rewatch

Build

$ rebar3 compile

Usage

Warning! Erwatch (currently) uses polling to determine file system changes. Setting the poll interval too frequent (lower) is not recommended for wildcards which may return a large number of paths.

Erwatch supports both the synchronous/on demand and asynchronous/message based way of tracking changes.

Use erwatch:new/0 to create a watch with default options, or erwatch:new/1 to create a watch with specified options:

% on demand watch:
{ok, Watch} = erwatch:new(),
% a watch that fires every 3000 milliseconds, and sends a message on changes
{ok, AnotherWatch} = erwatch:new([{interval, 3000}]).

You can add any wildcard to the watch. See filelib:wildcard/1 documentation for available patterns. Note that, the given wildcard is relative to the current working directory.

erwatch:add_wildcard("/tmp/somedir/**/src/*.erl", Watch).

Whether you use synchronous or asynchronous watches, the change sets are in the form of list of {Action, Path} pairs, where Action is one of added, updated or deleted. Note that, the very first change set will contain all resolved paths in the given wildcards.

You can change the poll interval and switch between synchronous and asynchronous modes using erwatch:set_interval/2. An interval of 0 will make the watch synchronous and > 0 will make it asynchronous.

erwatch:set_interval(1000, Watch).

It is possible to pause an asynchronous watch using erwatch:pause/1 and resume it using erwatch:resume/1.

erwatch:pause(Watch),
% later...
erwatch:resume(Watch).

When the time comes, you can kill a watch with erwatch:remove/1:

erwatch:remove(Watch).

Synchronous / On Demand Usage

Create a watch:

{ok, Watch} = erwatch:new().

Add one or more wildcards to the watch:

erwatch:add_wildcard("/tmp/foo1/*", Watch),
erwatch:add_wildcard("/tmp/bar2", Watch),

Assuming /tmp/foo1 is a directory and /tmp/bar2 is a file, create, modify, delete directories, files in /tmp/foo1 and/or create, modify, delete /tmp/bar2.

Retrieve changes:

erwatch:get_changes(Watch).

Returns e.g.:

[{added,"/tmp/foo1/myfile"},
 {updated,"/tmp/foo1/yourfile"},
 {updated,"/tmp/foo1/x"},
 {deleted,"/tmp/bar2"}]

Asynchronous / Message Based Usage

In this mode, Erwatch will send erwatch@changes messages to the parent process (currently the process which created the watch) on file system changes.

Create a watch with an interval:

{ok, Watch} = erwatch:new([{interval, 1000}]).

Add one or more wildcards to the watch:

erwatch:add_wildcard("/tmp/foo1/*", Watch),
erwatch:add_wildcard("/tmp/bar2", Watch),

Assuming /tmp/foo1 is a directory and /tmp/bar2 is a file, create, modify, delete directories, files in /tmp/foo1 and/or create, modify, delete /tmp/bar2.

Receive changes:

loop() ->
    receive
        {erwatch@changes, Watch, ChangeSet} ->
            % do something with `ChangeSet`
            loop()
        _ ->
            % received some other message...
            loop()
    end.

The ChangeSet value might be:

[{added,"/tmp/foo1/myfile"},
 {updated,"/tmp/foo1/yourfile"},
 {updated,"/tmp/foo1/x"},
 {deleted,"/tmp/bar2"}]

Examples

See examples/erwatch.escript for a simple file watcher.

License

Copyright (c) 2016, Yuce Tekol <yucetekol@gmail.com>.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

* Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.

* The names of its contributors may not be used to endorse or promote
  products derived from this software without specific prior written
  permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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