1erl_call(1) User Commands erl_call(1)
2
6 erl_call - Call/start a distributed Erlang node.
7
9 erl_call makes it possible to start and/or communicate with a distrib‐
10 uted Erlang node. It is built upon the Erl_Interface library as an ex‐
11 ample application. Its purpose is to use a Unix shell script to inter‐
12 act with a distributed Erlang node. It performs all communication with
13 the Erlang rex server, using the standard Erlang RPC facility. It does
14 not require any special software to be run at the Erlang target node.
15 The main use is to either start a distributed Erlang node or to make an
17 ordinary function call. However, it is also possible to pipe an Erlang
18 module to erl_call and have it compiled, or to pipe a sequence of Er‐
19 lang expressions to be evaluated (similar to the Erlang shell).
20 Options, which cause stdin to be read, can be used with advantage, as
22 scripts from within (Unix) shell scripts. Another nice use of erl_call
23 could be from (HTTP) CGI-bin scripts.
24
26 erl_call <options>
27 Starts/calls Erlang.
29 Each option flag is described below with its name, type, and
31 meaning.
32 -a [Mod [Fun [Args]]]]:
34 (Optional.) Applies the specified function and returns the
35 result. Mod must be specified. However, start and [] are as‐
36 sumed for unspecified Fun and Args, respectively. Args is to
37 be in the same format as for erlang:apply/3 in ERTS except
38 only a subset of all terms are allowed. The allowed term
39 types are: list (and string representation of list, that is
40 "example"), tuple, atom and number.
41 Notice that this flag takes exactly one argument, so quoting
43 can be necessary to group Mod, Fun, and Args in a manner de‐
44 pendent on the behavior of your command shell.
45 -address [Hostname:]Port:
47 (One of -n, -name, -sname or -address is required.) Hostname
48 is the hostname of the machine that is running the peer node
49 that erl_call shall communicate with. The default hostname
50 is the hostname of the local machine. Port is the port num‐
51 ber of the node that erl_call shall communicate with. The
52 -address flag cannot be combined with any of the flags -n,
53 -name, -sname or -s.
54 The -address flag is typically useful when one wants to call
56 a node that is running on machine without an accessible epmd
57 instance.
58 -c Cookie:
60 (Optional.) Use this option to specify a certain cookie. If
61 no cookie is specified, the ~/.erlang.cookie file is read
62 and its content is used as cookie. The Erlang node we want
63 to communicate with must have the same cookie.
64 -d:
66 (Optional.) Debug mode. This causes all I/O to be output to
67 the ~/.erl_call.out.Nodename file, where Nodename is the
68 node name of the Erlang node in question.
69 -e:
71 (Optional.) Reads a sequence of Erlang expressions, sepa‐
72 rated by comma (,) and ended with a full stop (.), from
73 stdin until EOF (Control-D). Evaluates the expressions and
74 returns the result from the last expression. Returns {ok,Re‐
75 sult} on success.
76 -fetch_stdout:
78 (Optional.) Executes the code, specified with the -a or -e
79 option, in a new process that has a group leader that for‐
80 wards all stdout (standard output) data so that it is
81 printed to stdout of the erl_call process. This means that
82 stdout data that are written during the execution of the
83 called code, by the code and by descendant processes, will
84 be forwarded (given that the group leader has not been
85 changed by a call to erlang:group_leader/2).
86 The printed data is UTF-8 encoded.
88 This option is only relevant together with the option -a or
90 -e.
91 See the documentation of the I/O protocol, for more informa‐
93 tion about the group leader concept.
94 Note:
96 This option only works when erl_call is interacting with a
97 node with a version greater or equal to OTP-24.
98 -h HiddenName:
101 (Optional.) Specifies the name of the hidden node that
102 erl_call represents.
103 -m:
105 (Optional.) Reads an Erlang module from stdin and compiles
106 it.
107 -n Node:
109 (One of -n, -name, -sname or -address is required.) Has the
110 same meaning as -name and can still be used for backward
111 compatibility reasons.
112 -name Node:
114 (One of -n, -name, -sname or -address is required.) Node is
115 the name of the peer node to be started or communicated
116 with. It is assumed that Node is started with erl -name,
117 which means that fully qualified long node names are used.
118 If option -s is specified, an Erlang node will (if neces‐
119 sary) be started with erl -name.
120 -no_result_term:
122 (Optional.) Do not print the result term. This option is
123 only relevant together with the options -a and -e.
124 -q:
126 (Optional.) Halts the Erlang node specified with switch -n.
127 This switch overrides switch -s.
128 -r:
130 (Optional.) Generates a random name of the hidden node that
131 erl_call represents.
132 -R:
134 (Optional.) Request a dynamic random name, of the hidden
135 node that erl_call represents, from the peer node. Supported
136 since OTP 23. Prefer -R over -r when doing repeated requests
137 toward the same peer node.
138 -s:
140 (Optional.) Starts a distributed Erlang node if necessary.
141 This means that in a sequence of calls, where '-s' and '-n
142 Node' are constant, only the first call starts the Erlang
143 node. This makes the rest of the communication very fast.
144 This flag is currently only available on Unix-like platforms
145 (Linux, Mac OS X, Solaris, and so on).
146 -sname Node:
148 (One of -n, -name, -sname or -address is required.) Node is
149 the name of the peer node to be started or communicated
150 with. It is assumed that Node is started with erl -sname,
151 which means that short node names are used. If option -s is
152 specified, an Erlang node is started (if necessary) with erl
153 -sname.
154 -timeout Seconds:
156 (Optional.) Aborts the erl_call process after the timeout
157 expires. Note that this does not abort commands that have
158 already been started with -a, -e, or similar.
159 -v:
161 (Optional.) Prints a lot of verbose information. This is
162 only useful for the developer and maintainer of erl_call.
163 -x ErlScript:
165 (Optional.) Specifies another name of the Erlang startup
166 script to be used. If not specified, the standard erl
167 startup script is used.
168
170 To start an Erlang node and call erlang:time/0:
171 erl_call -s -a 'erlang time' -n madonna
173 {18,27,34}
174 To terminate an Erlang node by calling erlang:halt/0:
177 erl_call -s -a 'erlang halt' -n madonna
179 To apply with many arguments:
182 erl_call -s -a 'lists seq [1,10]' -n madonna
184 To evaluate some expressions (the input ends with EOF (Control-D)):
187 erl_call -s -e -n madonna
189 statistics(runtime),
190 X=1,
191 Y=2,
192 {_,T}=statistics(runtime),
193 {X+Y,T}.
194 ^D
195 {ok,{3,0}}
196 To compile a module and run it (again, the input ends with EOF (Con‐
199 trol-D)):
200 (In the example, the output has been formatted afterwards.)
202 erl_call -s -m -a procnames -n madonna
204 -module(procnames).
205 -compile(export_all).
206 start() ->
207 P = processes(),
208 F = fun(X) -> {X,process_info(X,registered_name)} end,
209 lists:map(F,[],P).
210 ^D
211 [{<madonna@chivas.du.etx.ericsson.se,0,0>,
212 {registered_name,init}},
213 {<madonna@chivas.du.etx.ericsson.se,2,0>,
214 {registered_name,erl_prim_loader}},
215 {<madonna@chivas.du.etx.ericsson.se,4,0>,
216 {registered_name,error_logger}},
217 {<madonna@chivas.du.etx.ericsson.se,5,0>,
218 {registered_name,application_controller}},
219 {<madonna@chivas.du.etx.ericsson.se,6,0>,
220 {registered_name,kernel}},
221 {<madonna@chivas.du.etx.ericsson.se,7,0>,
222 []},
223 {<madonna@chivas.du.etx.ericsson.se,8,0>,
224 {registered_name,kernel_sup}},
225 {<madonna@chivas.du.etx.ericsson.se,9,0>,
226 {registered_name,net_sup}},
227 {<madonna@chivas.du.etx.ericsson.se,10,0>,
228 {registered_name,net_kernel}},
229 {<madonna@chivas.du.etx.ericsson.se,11,0>,
230 []},
231 {<madonna@chivas.du.etx.ericsson.se,12,0>,
232 {registered_name,global_name_server}},
233 {<madonna@chivas.du.etx.ericsson.se,13,0>,
234 {registered_name,auth}},
235 {<madonna@chivas.du.etx.ericsson.se,14,0>,
236 {registered_name,rex}},
237 {<madonna@chivas.du.etx.ericsson.se,15,0>,
238 []},
239 {<madonna@chivas.du.etx.ericsson.se,16,0>,
240 {registered_name,file_server}},
241 {<madonna@chivas.du.etx.ericsson.se,17,0>,
242 {registered_name,code_server}},
243 {<madonna@chivas.du.etx.ericsson.se,20,0>,
244 {registered_name,user}},
245 {<madonna@chivas.du.etx.ericsson.se,38,0>,
246 []}]
247 To forward standard output without printing the result term (again, the
250 input ends with EOF (Control-D)):
251 erl_call -s -e -sname madonna -fetch_stdout -no_result_term
253 io:format("Number of schedulers: ~p~n", [erlang:system_info(schedulers)]),
254 io:format("Number of logical cores: ~p~n", [erlang:system_info(logical_processors_available)]).
255 ^D
256 Number of schedulers: 8
257 Number of logical cores: 8
258Ericsson AB erl_interface 5.3 erl_call(1)