[erlang-questions] Can werl be detached?

Dan Gudmundsson <>
Tue May 31 08:25:26 CEST 2016


On Mon, May 30, 2016 at 11:49 PM John R. Ashmun <>
wrote:

> Now, running under R18.2 and Windows 10, I get a popup error message
> window that says
>
> "Werl
>
> Failed to execute erl:  The system cannot find the file specified."
>
> unless the current directory for the command prompt is "c:\Program
> Files\erl7.3\erts-7.3\bin".
>
> This is really similar to the restriction that Danial Goertzen pointed out
> about R15 albeit with an error message about a different file that's in
> ...\erts-(Vsn)\bin.  Could werl be changed to look in the directory near
> its own location rather than the current directory?  Further, it appears
> that erl.exe and werl.exe are each duplicated between ..\erl7.3\bin and
> ..erl7.3\erts-7.3\bin, for what purpose I am unsure, yet if werl were able
> to find itself, it could certainly find erl.exe.
>
> When the current directory is set to ..\erts-7.3\bin and I enter
>
> werl -detached -run wx demo
>
> the demo runs admirably, but after I close its window, a Windows process
> "erl" continues to run.  Doubtless this is the detached VM, but how do I
> explain to naive game users its continuation and the need to stop it using,
> e.g., Task Manager?
>
> These startup questions have led me to the init module and its boot/1 and
> stop/0 & stop/1 functions.  I think I would like my release's init process
> to call stop( ) when my game stops.  Is there a handy example of the use of
> init:stop( )?
>
>
Calling erlang:halt() will halt the erlang machine, but we can not call
that for obvious reasons in wx demo.


> Regards,
> John Ashmun
>
>
> On Wed, May 25, 2016 at 1:22 PM, Dan Gudmundsson <> wrote:
>
>> Hmm,
>> It works fine for me on Windows 10 from msys2 with erlang in the path
>> and from cmd shell without erlang in the path:
>>
>> C:\Users\familjen>"c:\Program Files (x86)\erl7.3\bin\werl" -run wx demo
>>
>> C:\Users\familjen>"c:\Program Files (x86)\erl7.3\bin\werl" -detached -run
>> wx demo
>>
>> Oh noticed the version you are running...
>>
>> It also works for me with 17.0 i.e. erl-6.0 which is the oldest I have
>> installed here at home.
>>
>> Why are you using an old version of erlang?
>> Can you try a newer version and see if that works?
>>
>>
>> On Wed, May 25, 2016 at 9:49 PM John Ashmun <>
>> wrote:
>>
>>> I just found time to try what you suggested with the wx demo, but I got
>>> the same pop up Windows error message as when I try to run my release with
>>> -detached.
>>>
>>> I added ...\erts-5.9\bin to %Path% and tried again but it failed again
>>> with the same error message.
>>>
>>> Sent from my iPhone
>>>
>>> On May 18, 2016, at 12:02 AM, Dan Gudmundsson <> wrote:
>>>
>>> At least this works as it should:
>>>
>>> werl -detached -run wx demo
>>>
>>>
>>> On Wed, May 18, 2016 at 3:48 AM John R. Ashmun <>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Tue, May 17, 2016 at 6:32 PM, zxq9 <> wrote:
>>>>
>>>>> On Tuesday 17 May 2016 16:47:35 John R. Ashmun wrote:
>>>>> > Perhaps my subject is not quite the correct question.  Here's my
>>>>> context:
>>>>> >
>>>>> > I'm beginning to recreate in Erlang on Microsoft Windows 10 a public
>>>>> domain
>>>>> > program I used to enjoy on my Commodore Amiga:  mATC was a game in
>>>>> which
>>>>> > the user acted as a military Air Traffic Controller.  I am using a wx
>>>>> > window to draw the player's map with aircraft data blocks overlaid.
>>>>> I
>>>>> > don't have a use for the initial window that opens when werl is
>>>>> started.
>>>>>
>>>>> Awesome!
>>>>>
>>>>> > If I use this Command Prompt batch file, mATC.bat:
>>>>> >
>>>>> > werl -pa ebin -pa mATC_app\ebin -detached -boot mATC -config sys
>>>>> >
>>>>> > a Windows error message window appears that says:
>>>>> >
>>>>> > "Failed to execute C:\Program Files\erl5.9\erts5.9\bin\beam.smp.dll
>>>>> >  The system cannot find the file specified."
>>>>> >
>>>>> > The DLL is actually present at that location, and of course
>>>>> everything runs
>>>>> > well when I don't use -detached.
>>>>>
>>>>> Hrm... that seems odd, but I have to admit I have no experience running
>>>>> actual releases on Windows. What I usually do instead is have the
>>>>> runtime
>>>>> installed on the Windows machine, unpack project code and kick things
>>>>> off
>>>>> with an escript that builds and then launches the code I want to run.
>>>>>
>>>>> Changing from releases to from-source build->run may require a bit of
>>>>> shuffling -- and may or may not be worth it depending on the project.
>>>>> But this has been very effective and lightweight for my purposes.
>>>>>
>>>>> Like everything else on Windows there are a few quirks to making
>>>>> escripts
>>>>> a click-to-run experience (specifying full path to "escript.exe"
>>>>> instead
>>>>> of "escript" in your launcher, space for unheeded shebang, etc.). I've
>>>>> wanted for a few years now to formalize and simplify a solution to
>>>>> this...
>>>>> but real life gets in the way of the things I wish I could do as
>>>>> community
>>>>> project work. :-(
>>>>>
>>>>> The escript-to-bootstrap approach has made my Erlang GUI experience on
>>>>> Windows fairly painless -- I can develop on Linux or BSD and almost
>>>>> always
>>>>> get away with relying on anything that works there (to include wx)
>>>>> working
>>>>> pretty much the same way on Windows.
>>>>>
>>>>> I have not tried this on Windows 10 yet, but I assume it will continue
>>>>> to
>>>>> work the same way it does on Windows 7 and 8.1.
>>>>>
>>>>> -Craig
>>>>> _______________________________________________
>>>>> erlang-questions mailing list
>>>>> 
>>>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>>>
>>>>
>>>> I will look into escript, thanks.
>>>>
>>>> John
>>>> _______________________________________________
>>>> erlang-questions mailing list
>>>> 
>>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>>
>>>
>
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