Erwatch

Erwatch is an Erlang/OTP application for tracking changes in a file system. It can be used with 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.

News

• 2016-03-08: Major change in Erwatch API.
  • Removed erwatch:add_wildcard/2 function. You have to specify the wildcards to erwatch:new/1 or erwatch:new/2 instead.
  • The initial changesets are not returned. Use filelib:wildcard/1 or filelib:wildcard/2 instead.

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]}.

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.

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
   ]},
...

Or, start it manually:

ok = application:start(erwatch).

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

$ rebar3 shell --apps rewatch

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

Use erwatch:new/1 to create a watch with default options, or erwatch:new/2 to create a watch with specified options. The list of wildcards is mandatory for both:

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

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

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.

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(["/tmp/foo1/*", "/tmp/bar2"]).

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(["/tmp/foo1/*", "/tmp/bar2"],
                          [{interval, 1000}]).

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/watch.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,
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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