init

Command Line Flags

The support for loading of code from archive files is experimental. The sole purpose of releasing it before it is ready is to obtain early feedback. The file format, semantics, interfaces etc. may be changed in a future release. The -code_path_choice flag is also experimental.

The init module interprets the following command line flags:

Everything following -- up to the next flag is considered plain arguments and can be retrieved using get_plain_arguments/0.

-code_path_choice Choice

This flag can be set to strict or relaxed. It controls whether each directory in the code path should be interpreted strictly as it appears in the boot script or if init should be more relaxed and try to find a suitable directory if it can choose from a regular ebin directory and an ebin directory in an archive file. This flag is particular useful when you want to elaborate with code loading from archives without editing the boot script. See script(4) for more information about interpretation of boot scripts. The flag does also have a similar affect on how the code server works. See code(3).

-eval Expr

Scans, parses and evaluates an arbitrary expression Expr during system initialization. If any of these steps fail (syntax error, parse error or exception during evaluation), Erlang stops with an error message. Here is an example that seeds the random number generator:

% erl -eval '{X,Y,Z}' = now(), random:seed(X,Y,Z).'

This example uses Erlang as a hexadecimal calculator:

% erl -noshell -eval 'R = 16#1F+16#A0, io:format("~.16B~n", [R])' \\
-s erlang halt
BF

If multiple -eval expressions are specified, they are evaluated sequentially in the order specified. -eval expressions are evaluated sequentially with -s and -run function calls (this also in the order specified). As with -s and -run, an evaluation that does not terminate, blocks the system initialization process.

-extra

Everything following -extra is considered plain arguments and can be retrieved using get_plain_arguments/0.

-run Mod [Func [Arg1, Arg2, ...]]

Evaluates the specified function call during system initialization. Func defaults to start. If no arguments are provided, the function is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, taking the list [Arg1,Arg2,...] as argument. All arguments are passed as strings. If an exception is raised, Erlang stops with an error message.

Example:

% erl -run foo -run foo bar -run foo bar baz 1 2

This starts the Erlang runtime system and evaluates the following functions:


foo:start()
foo:bar()
foo:bar(["baz", "1", "2"]).

The functions are executed sequentially in an initialization process, which then terminates normally and passes control to the user. This means that a -run call which does not return will block further processing; to avoid this, use some variant of spawn in such cases.

-s Mod [Func [Arg1, Arg2, ...]]

Evaluates the specified function call during system initialization. Func defaults to start. If no arguments are provided, the function is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, taking the list [Arg1,Arg2,...] as argument. All arguments are passed as atoms. If an exception is raised, Erlang stops with an error message.

Example:

% erl -s foo -s foo bar -s foo bar baz 1 2

This starts the Erlang runtime system and evaluates the following functions:


foo:start()
foo:bar()
foo:bar([baz, '1', '2']).

The functions are executed sequentially in an initialization process, which then terminates normally and passes control to the user. This means that a -s call which does not return will block further processing; to avoid this, use some variant of spawn in such cases.

Due to the limited length of atoms, it is recommended that -run be used instead.

% erl -- a b -children thomas claire -ages 7 3 -- x y ... 1> init:get_plain_arguments(). ["a","b","x","y"] 2> init:get_argument(children). {ok,[["thomas","claire"]]} 3> init:get_argument(ages). {ok, [["7","3"]]} 4> init:get_argument(silly). error