# erl_call

### COMMAND

erl_call

### COMMAND SUMMARY

Call/Start a Distributed Erlang Node

### DESCRIPTION

`erl_call` makes it possible to start and/or communicate with a distributed Erlang node. It is built upon the `erl_interface` library as an example application. Its purpose is to use an Unix shell script to interact with a distributed Erlang node. It performs all communication with the Erlang rex server, using the standard Erlang RPC facility. It does not require any special software to be run at the Erlang target node.

The main use is to either start a distributed Erlang node or to make an ordinary function call. However, it is also possible to pipe an Erlang module to `erl_call` and have it compiled, or to pipe a sequence of Erlang expressions to be evaluated (similar to the Erlang shell).

Options, which cause `stdin` to be read, can be used with advantage as scripts from within (Unix) shell scripts. Another nice use of `erl_call` could be from (http) CGI-bin scripts.

### EXPORTS

`erl_call <options>`

Each option flag is described below with its name, type and meaning.

-a [Mod [Fun [Args]]]]
  (optional): Applies the specified function and returns the result. `Mod` must be specified, however [] is assumed for unspecified `Fun` and `Args`. `Args` should be in the same format as for `erlang:apply/3`. Note that this flag takes exactly one argument, so quoting may be necessary in order to group `Mod`, `Fun` and `Args`, in a manner dependent on the behavior of your command shell.
-c Cookie
  (optional): Use this option to specify a certain cookie. If no cookie is specified, the `~/.erlang.cookie` file is read and its content are used as cookie. The Erlang node we want to communicate with must have the same cookie.
-d
  (optional): Debug mode. This causes all IO to be output to the file `~/.erl_call.out.Nodename`, where `Nodename` is the node name of the Erlang node in question.
-e
  (optional): Reads a sequence of Erlang expressions, separated by ',' and ended with a '.', from `stdin` until EOF (Control-D). Evaluates the expressions and returns the result from the last expression. Returns `{ok,Result}` if successful.
-h HiddenName
  (optional): Specifies the name of the hidden node that `erl_call` represents.
-m
  (optional): Reads an Erlang module from `stdin` and compiles it.
-n Node
  (one of `-n, -name, -sname` is required): Has the same meaning as `-name` and can still be used for backwards compatibility reasons.
-name Node
  (one of `-n, -name, -sname` is required): `Node` is the name of the node to be started or communicated with. It is assumed that `Node` is started with `erl -name`, which means that fully qualified long node names are used. If the `-s` option is given, an Erlang node will (if necessary) be started with `erl -name`.
-q
  (optional): Halts the Erlang node specified with the -n switch. This switch overrides the -s switch.
-r
  (optional): Generates a random name of the hidden node that `erl_call` represents.
-s
  (optional): Starts a distributed Erlang node if necessary. This means that in a sequence of calls, where the '`-s`' and '`-n Node`' are constant, only the first call will start the Erlang node. This makes the rest of the communication very fast. This flag is currently only available on the Unix platform.
-sname Node
  (one of `-n, -name, -sname` is required): `Node` is the name of the node to be started or communicated with. It is assumed that `Node` is started with `erl -sname` which means that short node names are used. If `-s` option is given, an Erlang node will be started (if necessary) with `erl -sname`.
-v
  (optional): Prints a lot of `verbose` information. This is only useful for the developer and maintainer of `erl_call`.
-x ErlScript
  (optional): Specifies another name of the Erlang start-up script to be used. If not specified, the standard `erl` start-up script is used.

### Examples

Starts an Erlang node and calls `erlang:time/0`.

    erl_call -s -a 'erlang time' -n madonna
    {18,27,34}

Terminates an Erlang node by calling `erlang:halt/0`.

    erl_call -s -a 'erlang halt' -n madonna

An apply with several arguments.

    erl_call -s -a 'lists map [{math,sqrt},[1,4,9,16,25]]' -n madonna

Evaluates a couple of expressions. The input ends with EOF (Control-D).

    erl_call -s -e -n madonna
    statistics(runtime),
    X=1,
    Y=2,
    {_,T}=statistics(runtime),
    {X+Y,T}.
    ^D
    {ok,{3,0}}

Compiles a module and runs it. Again, the input ends with EOF (Control-D). (In the example shown, the output has been formatted afterwards).

    erl_call -s -m -a lolita -n madonna
    -module(lolita).
    -compile(export_all).
    start() ->
            P = processes(),
            F = fun(X) -> {X,process_info(X,registered_name)} end,
            lists:map(F,[],P).
    ^D
    [{<madonna@chivas.du.etx.ericsson.se,0,0>,
                      {registered_name,init}},
     {<madonna@chivas.du.etx.ericsson.se,2,0>,
                      {registered_name,erl_prim_loader}},
     {<madonna@chivas.du.etx.ericsson.se,4,0>,
                      {registered_name,error_logger}},
     {<madonna@chivas.du.etx.ericsson.se,5,0>,
                      {registered_name,application_controller}},
     {<madonna@chivas.du.etx.ericsson.se,6,0>,
                      {registered_name,kernel}},
     {<madonna@chivas.du.etx.ericsson.se,7,0>,
                      []},
     {<madonna@chivas.du.etx.ericsson.se,8,0>,
                      {registered_name,kernel_sup}},
     {<madonna@chivas.du.etx.ericsson.se,9,0>,
                      {registered_name,net_sup}},
     {<madonna@chivas.du.etx.ericsson.se,10,0>,
                      {registered_name,net_kernel}},
     {<madonna@chivas.du.etx.ericsson.se,11,0>,
                      []},
     {<madonna@chivas.du.etx.ericsson.se,12,0>,
                      {registered_name,global_name_server}},
     {<madonna@chivas.du.etx.ericsson.se,13,0>,
                      {registered_name,auth}},
     {<madonna@chivas.du.etx.ericsson.se,14,0>,
                      {registered_name,rex}},
     {<madonna@chivas.du.etx.ericsson.se,15,0>,
                      []},
     {<madonna@chivas.du.etx.ericsson.se,16,0>,
                      {registered_name,file_server}},
     {<madonna@chivas.du.etx.ericsson.se,17,0>,
                      {registered_name,code_server}},
     {<madonna@chivas.du.etx.ericsson.se,20,0>,
                      {registered_name,user}},
     {<madonna@chivas.du.etx.ericsson.se,38,0>,
                      []}]

### AUTHORS

T.Törnkvist - support@erlang.ericsson.se

erl_interface 3.5.5
Copyright © 1991-2006 Ericsson AB