[erlang-questions] [Erlang-Q] What does Ctrl+G do for the Eshell?

Barco You <>
Tue Oct 4 08:31:21 CEST 2011


Such a fabulous facility! Thank-you for telling!
On Oct 4, 2011 6:13 AM, "Anders Ramsell" <> wrote:
> Barco You wrote:
>> Hello Erlangers,
>>
>> When starting a erl shell, we will see a printout as:
>> Eshell V5.8.4 (abort with ^G)
>>
>>
>> then, I tried to press Ctrl+G and got:
>> User switch command
>> --> ls
>> Unknown command
>> --> q().
>> Unknown command
>> -->
>>
>> I can do nothing with the prompt "-->". How to quit from it? and
>> what's "Ctrl+G" used for?
>>
>>
> The words "abort with ^G" are in fact hiding an extremely useful
> function called JCL (job control mode) [1]. I overlooked this
> function for years. Now I use it on a near daily basis and just
> love it.
>
> [1] http://www.erlang.org/doc/man/shell.html
>
> Assume you have an Erlang node named '' running as a
> service/daemon on your system. Wouldn't it be great if you could
> run interactive commands on this node just like you do in a
> shell? JCL let's you do that with ease.
>
> Start up a new shell '' and hit ctrl-G to enter JCL.
> Now start a remote shell to ''.
>
> | ()1>
> | User switch command
> | --> r 
> | --> j
> | 1* {shell,start,[init]}
> | 2 {,shell,start,[]}
>
> You now have a local shell with id=1 and a remote shell with
> id=2. Connect to the remote shell:
>
> | --> c 2
> |
> | ()1>
>
> Now you have a shell on the server node where you can run any
> command you want. This means you can call any exported function
> in all modules loaded on the server. That kind of interaction
> with a running system can be invaluable when trying to figure out
> why it doesn't behave quite the way you planned.
>
> Now of course there is a backside to the story. Doing something
> wrong may cause your system to crash. So hey - let's be careful
> out there.
>
> /Anders
>
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