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NAME
erl - The Erlang Emulator
DESCRIPTION
The erl program starts an Erlang runtime system. The exact details (for
example, whether erl is a script or a program and which other programs
it calls) are system-dependent.
Windows users probably wants to use the werl program instead, which
runs in its own window with scrollbars and supports command-line
editing. The erl program on Windows provides no line editing in its
shell, and on Windows 95 there is no way to scroll back to text which
has scrolled off the screen. The erl program must be used, however, in
pipelines or if you want to redirect standard input or output.
EXPORTS
erl <arguments>
Starts an Erlang runtime system.
The arguments can be divided into emulator flags, flags and
plain arguments:
* Any argument starting with the character + is interpreted as
an emulator flag.
As indicated by the name, emulator flags controls the
behavior of the emulator.
* Any argument starting with the character - (hyphen) is
interpreted as a flag which should be passed to the Erlang
part of the runtime system, more specifically to the init
system process, see init(3).
The init process itself interprets some of these flags, the
init flags. It also stores any remaining flags, the user
flags. The latter can be retrieved by calling
init:get_argument/1.
It can be noted that there are a small number of "-" flags
which now actually are emulator flags, see the description
below.
* Plain arguments are not interpreted in any way. They are
also stored by the init process and can be retrieved by
calling init:get_plain_arguments/0. Plain arguments can
occur before the first flag, or after a -- flag.
Additionally, the flag -extra causes everything that follows
to become plain arguments.
Example:
%erl +W w -sname arnie +R 9 -s my_init -extra +bertie
(arnie@host)1>init:get_argument(sname).
{ok,[["arnie"]]}
(arnie@host)2>init:get_plain_arguments().
["+bertie"]
Here +W w and +R 9 are emulator flags. -s my_init is an init
flag, interpreted by init. -sname arnie is a user flag, stored
by init. It is read by Kernel and will cause the Erlang runtime
system to become distributed. Finally, everything after -extra
(that is, +bertie) is considered as plain arguments.
%erl -myflag 1
1>init:get_argument(myflag).
{ok,[["1"]]}
2>init:get_plain_arguments().
[]
Here the user flag -myflag 1 is passed to and stored by the init
process. It is a user defined flag, presumably used by some user
defined application.
Flags
In the following list, init flags are marked (init flag). Unless
otherwise specified, all other flags are user flags, for which the
values can be retrieved by calling init:get_argument/1. Note that the
list of user flags is not exhaustive, there may be additional,
application specific flags which instead are documented in the
corresponding application documentation.
-- (init flag):
Everything following -- up to the next flag (-flag or +flag) is
considered plain arguments and can be retrieved using
init:get_plain_arguments/0.
-Application Par Val:
Sets the application configuration parameter Par to the value Val
for the application Application, see app(4) and application(3).
-args_file FileName:
Command line arguments are read from the file FileName. The
arguments read from the file replace the ’-args_file FileName’
flag on the resulting command line.
The file FileName should be a plain text file and may contain
comments and command line arguments. A comment begins with a #
character and continues until next end of line character.
Backslash (\) is used as quoting character. All command line
arguments accepted by erl are allowed, also the -args_file
FileName flag. Be careful not to cause circular dependencies
between files containing the -args_file flag, though.
The -extra flag is treated specially. Its scope ends at the end
of the file. Arguments following an -extra flag are moved on the
command line into the -extra section, i.e. the end of the command
line following after an -extra flag.
-async_shell_start:
The initial Erlang shell does not read user input until the
system boot procedure has been completed (Erlang 5.4 and later).
This flag disables the start synchronization feature and lets the
shell start in parallel with the rest of the system.
-boot File:
Specifies the name of the boot file, File.boot, which is used to
start the system. See init(3). Unless File contains an absolute
path, the system searches for File.boot in the current and
$ROOT/bin directories.
Defaults to $ROOT/bin/start.boot.
-boot_var Var Dir:
If the boot script contains a path variable Var other than $ROOT,
this variable is expanded to Dir. Used when applications are
installed in another directory than $ROOT/lib, see
systools:make_script/1,2.
-code_path_cache:
Enables the code path cache of the code server, see code(3).
-compile Mod1 Mod2 ...:
Compiles the specified modules and then terminates (with non-zero
exit code if the compilation of some file did not succeed).
Implies -noinput. Not recommended - use erlc instead.
-config Config:
Specifies the name of a configuration file, Config.config, which
is used to configure applications. See app(4) and application(3).
-connect_all false:
If this flag is present, global will not maintain a fully
connected network of distributed Erlang nodes, and then global
name registration cannot be used. See global(3).
-cookie Cookie:
Obsolete flag without any effect and common misspelling for
-setcookie. Use -setcookie instead.
-detached:
Starts the Erlang runtime system detached from the system
console. Useful for running daemons and backgrounds processes.
-emu_args:
Useful for debugging. Prints out the actual arguments sent to the
emulator.
-env Variable Value:
Sets the host OS environment variable Variable to the value Value
for the Erlang runtime system. Example:
%erl -env DISPLAY gin:0
In this example, an Erlang runtime system is started with the
DISPLAY environment variable set to gin:0.
-eval Expr (init flag):
Makes init evaluate the expression Expr, see init(3).
-extra (init flag):
Everything following -extra is considered plain arguments and can
be retrieved using init:get_plain_arguments/0.
-heart:
Starts heart beat monitoring of the Erlang runtime system. See
heart(3).
-hidden:
Starts the Erlang runtime system as a hidden node, if it is run
as a distributed node. Hidden nodes always establish hidden
connections to all other nodes except for nodes in the same
global group. Hidden connections are not published on neither of
the connected nodes, i.e. neither of the connected nodes are part
of the result from nodes/0 on the other node. See also hidden
global groups, global_group(3).
-hosts Hosts:
Specifies the IP addresses for the hosts on which Erlang boot
servers are running, see erl_boot_server(3). This flag is
mandatory if the -loader inet flag is present.
The IP addresses must be given in the standard form (four decimal
numbers separated by periods, for example "150.236.20.74". Hosts
names are not acceptable, but a broadcast address (preferably
limited to the local network) is.
-id Id:
Specifies the identity of the Erlang runtime system. If it is run
as a distributed node, Id must be identical to the name supplied
together with the -sname or -name flag.
-init_debug:
Makes init write some debug information while interpreting the
boot script.
-instr (emulator flag):
Selects an instrumented Erlang runtime system (virtual machine)
to run, instead of the ordinary one. When running an instrumented
runtime system, some resource usage data can be obtained and
analysed using the module instrument. Functionally, it behaves
exactly like an ordinary Erlang runtime system.
-loader Loader:
Specifies the method used by erl_prim_loader to load Erlang
modules into the system. See erl_prim_loader(3). Two Loader
methods are supported, efile and inet. efile means use the local
file system, this is the default. inet means use a boot server on
another machine, and the -id, -hosts and -setcookie flags must be
specified as well. If Loader is something else, the user supplied
Loader port program is started.
-make:
Makes the Erlang runtime system invoke make:all() in the current
working directory and then terminate. See make(3). Implies
-noinput.
-man Module:
Displays the manual page for the Erlang module Module. Only
supported on Unix.
-mode interactive | embedded:
Indicates if the system should load code dynamically
(interactive), or if all code should be loaded during system
initialization (embedded), see code(3). Defaults to interactive.
-name Name:
Makes the Erlang runtime system into a distributed node. This
flag invokes all network servers necessary for a node to become
distributed. See net_kernel(3). It is also ensured that epmd runs
on the current host before Erlang is started. See epmd(1).
The name of the node will be Name@Host, where Host is the fully
qualified host name of the current host. For short names, use the
-sname flag instead.
-noinput:
Ensures that the Erlang runtime system never tries to read any
input. Implies -noshell.
-noshell:
Starts an Erlang runtime system with no shell. This flag makes it
possible to have the Erlang runtime system as a component in a
series of UNIX pipes.
-nostick:
Disables the sticky directory facility of the Erlang code server,
see code(3).
-oldshell:
Invokes the old Erlang shell from Erlang 3.3. The old shell can
still be used.
-pa Dir1 Dir2 ...:
Adds the specified directories to the beginning of the code path,
similar to code:add_pathsa/1. See code(3).
-pz Dir1 Dir2 ...:
Adds the specified directories to the end of the code path,
similar to code:add_pathsz/1. See code(3).
-remsh Node:
Starts Erlang with a remote shell connected to Node.
-rsh Program:
Specifies an alternative to rsh for starting a slave node on a
remote host. See slave(3).
-run Mod [Func [Arg1, Arg2, ...]] (init flag):
Makes init call the specified function. 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. See init(3).
-s Mod [Func [Arg1, Arg2, ...]] (init flag):
Makes init call the specified function. 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. See init(3).
-setcookie Cookie:
Sets the magic cookie of the node to Cookie, see
erlang:set_cookie/2.
-shutdown_time Time:
Specifies how long time (in milliseconds) the init process is
allowed to spend shutting down the system. If Time ms have
elapsed, all processes still existing are killed. Defaults to
infinity.
-sname Name:
Makes the Erlang runtime system into a distributed node, similar
to -name, but the host name portion of the node name Name@Host
will be the short name, not fully qualified.
This is sometimes the only way to run distributed Erlang if the
DNS (Domain Name System) is not running. There can be no
communication between nodes running with the -sname flag and
those running with the -name flag, as node names must be unique
in distributed Erlang systems.
-smp [enable|auto|disable]:
-smp enable and -smp starts the Erlang runtime system with SMP
support enabled. This may fail if no runtime system with SMP
support is available. -smp auto starts the Erlang runtime system
with SMP support enabled if it is available and more than one
logical processor are detected. -smp disable starts a runtime
system without SMP support. This is currently the default
behavior. -smp auto will probably be the default behavior some
time in the future.
NOTE: The runtime system with SMP support will not be available
on all supported platforms. See also the +S flag.
-version (emulator flag):
Makes the emulator print out its version number. The same as erl
+V.
Emulator Flags
erl invokes the code for the Erlang emulator (virtual machine), which
supports the following flags:
+a size:
Suggested stack size, in kilowords, for threads in the async-
thread pool. Valid range is 16-8192 kilowords. The default
suggested stack size is 16 kilowords, i.e, 64 kilobyte on 32-bit
architectures. This small default size has been chosen since the
amount of async-threads might be quite large. The default size is
enough for drivers delivered with Erlang/OTP, but might not be
sufficiently large for other dynamically linked in drivers that
use the driver_async() functionality. Note that the value passed
is only a suggestion, and it might even be ignored on some
platforms.
+A size:
Sets the number of threads in async thread pool, valid range is
0-1024. Default is 0.
+B [c | d | i]:
The c option makes Ctrl-C interrupt the current shell instead of
invoking the emulator break handler. The d option (same as
specifying +B without an extra option) disables the break
handler. The i option makes the emulator ignore any break signal.
If the c option is used with oldshell on Unix, Ctrl-C will
restart the shell process rather than interrupt it.
Note that on Windows, this flag is only applicable for werl, not
erl (oldshell). Note also that Ctrl-Break is used instead of
Ctrl-C on Windows.
+c: Disable compensation for sudden changes of system time.
Normally, erlang:now/0 will not immediately reflect sudden
changes in the system time, in order to keep timers (including
receive-after) working. Instead, the time maintained by
erlang:now/0 is slowly adjusted towards the new system time.
(Slowly means in one percent adjustments; if the time is off by
one minute, the time will be adjusted in 100 minutes.)
When the +c option is given, this slow adjustment will not take
place. Instead erlang:now/0 will always reflect the current
system time. Note that timers are based on erlang:now/0. If the
system time jumps, timers then time out at the wrong time.
+h Size:
Sets the default heap size of processes to the size Size.
+K true | false:
Enables or disables the kernel poll functionality if the emulator
supports it. Default is false (disabled). If the emulator does
not support kernel poll, and the +K flag is passed to the
emulator, a warning is issued at startup.
+l: Enables auto load tracing, displaying info while loading code.
+MFlag Value:
Memory allocator specific flags, see erts_alloc(3) for further
information.
+P Number:
Sets the maximum number of concurrent processes for this system.
Number must be in the range 16..134217727. Default is 32768.
+R ReleaseNumber:
Sets the compatibility mode.
The distribution mechanism is not backwards compatible by
default. This flags sets the emulator in compatibility mode with
an earlier Erlang/OTP release ReleaseNumber. The release number
must be in the range 7..<current release>. This limits the
emulator, making it possible for it to communicate with Erlang
nodes (as well as C- and Java nodes) running that earlier
release.
For example, an R10 node is not automatically compatible with an
R9 node, but R10 nodes started with the +R 9 flag can co-exist
with R9 nodes in the same distributed Erlang system, they are
R9-compatible.
Note: Make sure all nodes (Erlang-, C-, and Java nodes) of a
distributed Erlang system is of the same Erlang/OTP release, or
from two different Erlang/OTP releases X and Y, where all Y nodes
have compatibility mode X.
For example: A distributed Erlang system can consist of R10
nodes, or of R9 nodes and R9-compatible R10 nodes, but not of R9
nodes, R9-compatible R10 nodes and "regular" R10 nodes, as R9 and
"regular" R10 nodes are not compatible.
+r: Force ets memory block to be moved on realloc.
+S Number:
Sets the number of scheduler threads to use when SMP support has
been enabled. Valid range is 1-1024. If the Erlang runtime system
is able to determine the number of processor cores available, the
default value will equal the this value; otherwise, the default
value will be one.
This flag will be ignored if the emulator doesn’t have SMP
support enabled (see the -smp flag).
+T Level:
Enables modified timing and sets the modified timing level.
Currently valid range is 0-9. The timing of the runtime system
will change. A high level usually means a greater change than a
low level. Changing the timing can be very useful for finding
timing related bugs.
Currently, modified timing affects the following:
Process spawning:
A process calling spawn, spawn_link, spawn_monitor, or
spawn_opt will be scheduled out immediately after
completing the call. When higher modified timing levels are
used, the caller will also sleep for a while after being
scheduled out.
Context reductions:
The amount of reductions a process is a allowed to use
before being scheduled out is increased or reduced.
Input reductions:
The amount of reductions performed before checking I/O is
increased or reduced.
NOTE: Performance will suffer when modified timing is enabled.
This flag is only intended for testing and debugging. Also note
that return_to and return_from trace messages will be lost when
tracing on the spawn BIFs. This flag may be removed or changed at
any time without prior notice.
+V: Makes the emulator print out its version number.
+v: Verbose.
+W w | i:
Sets the mapping of warning messages for error_logger. Messages
sent to the error logger using one of the warning routines can be
mapped either to errors (default), warnings (+W w), or info
reports (+W i). The current mapping can be retrieved using
error_logger:warning_map/0. See error_logger(3) for further
information.
Environment variables
ERL_CRASH_DUMP:
If the emulator needs to write a crash dump, the value of this
variable will be the file name of the crash dump file. If the
variable is not set, the name of the crash dump file will be
erl_crash.dump in the current directory.
ERL_CRASH_DUMP_NICE:
Unix systems: If the emulator needs to write a crash dump, it
will use the value of this variable to set the nice value for the
process, thus lowering its priority. The allowable range is 1
through 39 (higher values will be replaced with 39). The highest
value, 39, will give the process the lowest priority.
ERL_CRASH_DUMP_SECONDS:
Unix systems: This variable gives the number of seconds that the
emulator will be allowed to spend writing a crash dump. When the
given number of seconds have elapsed, the emulator will be
terminated by a SIGALRM signal.
ERL_AFLAGS:
The content of this environment variable will be added to the
beginning of the command line for erl.
The -extra flag is treated specially. Its scope ends at the end
of the environment variable content. Arguments following an
-extra flag are moved on the command line into the -extra
section, i.e. the end of the command line following after an
-extra flag.
ERL_ZFLAGS and ERL_FLAGS:
The content of these environment variables will be added to the
end of the command line for erl.
The -extra flag is treated specially. Its scope ends at the end
of the environment variable content. Arguments following an
-extra flag are moved on the command line into the -extra
section, i.e. the end of the command line following after an
-extra flag.
See Also
init(3), erl_prim_loader(3), erl_boot_server(3), code(3),
application(3), heart(3), net_kernel(3), auth(3), make(3), epmd(1),
erts_alloc(3)
AUTHORS
Joe Armstrong - support@erlang.ericsson.se
Magnus Froberg - support@erlang.ericsson.se
Per Hedeland - support@erlang.ericsson.se
Sebastian Strollo - support@erlang.ericsson.se
Claes Wikstrom - support@erlang.ericsson.se
Mike Williams - support@erlang.ericsson.se
Robert Virding - support@erlang.ericsson.se
Rickard Green - support@erlang.ericsson.se