ERL_CALL(1) General Commands Manual ERL_CALL(1)

erl_call - Call/start a distributed Erlang node.

erl_call makes it possible to start and/or communicate with a distributed Erlang node. It is built on the Erl_Interface library as an example application. Its purpose is to use a 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.

Starts/calls Erlang.

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, start and [] are assumed for unspecified Fun and Args, respectively. Args is to be in the same format as for erlang:apply/3 in ERTS except only a subset of all terms are allowed. The allowed term types are: list (and string representation of list, that is "example"), tuple, atom and number.
Notice that this flag takes exactly one argument, so quoting can be necessary to group Mod, Fun, and Args in a manner dependent on the behavior of your command shell.
•
-address [Hostname:]Port - (One of -n, -name, -sname or -address is required.) Hostname is the hostname of the machine that is running the peer node that erl_call will communicate with. The default hostname is the hostname of the local machine. Port is the port number of the node that erl_call will communicate with. The -address flag cannot be combined with any of the flags -n, -name, -sname or -s.
The -address flag is typically useful when one wants to call a node that is running on machine without an accessible epmd instance.
The printed data is UTF-8 encoded.
This option is only relevant combined with the -a or -e option.
See the documentation of the I/O protocol for more information about the group leader concept.
Note
This option only works when erl_call is interacting with a node with a version greater or equal to OTP-24.

To start an Erlang node and call erlang:time/0:

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

To terminate an Erlang node by calling erlang:halt/0:

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

To apply with many arguments:

erl_call -s -a 'lists seq [1,10]' -n madonna

To evaluate some 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}}

To compile a module and run it (again, the input ends with EOF (Control-D)):

(In the example, the output has been formatted afterwards.)

erl_call -s -m -a procnames -n madonna
-module(procnames).
-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>,
                  []}]

To forward standard output without printing the result term (again, the input ends with EOF (Control-D)):

erl_call -s -e -sname madonna -fetch_stdout -no_result_term
io:format("Number of schedulers: ~p~n", [erlang:system_info(schedulers)]),
io:format("Number of logical cores: ~p~n", [erlang:system_info(logical_processors_available)]).
^D
Number of schedulers: 8
Number of logical cores: 8

January 2025