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.
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.
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:
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).
As an alternative to -pa, if several directories are
to be prepended to the code and the directories have a
common parent directory, that parent directory could be
specified in the ERL_LIBS environment variable.
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.
By default -smp auto will be used unless a conflicting
parameter has been passed, then -smp disable will be
used. Currently only the -hybrid parameter conflicts
with -smp auto.
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.
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.
-
+d
-
If the emulator detects an internal error (or runs out of memory),
it will by default generate both a crash dump and a core dump.
The core dump will, however, not be very useful since the content
of process heaps is destroyed by the crash dump generation.
The +d option instructs the emulator to only produce a
core dump and no crash dump if an internal error is detected.
Calling erlang:halt/1 with a string argument will still
produce a crash dump.
-
+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 Schedulers:SchedulerOnline
-
Sets the amount of scheduler threads to create and scheduler
threads to set online when SMP support has been enabled.
Valid range for both values are 1-1024. If the
Erlang runtime system is able to determine the amount
of logical processors configured and logical processors available,
Schedulers will default to logical processors configured,
and SchedulersOnline will default to logical processors
available; otherwise, the default values will be 1. Schedulers
may be omitted if :SchedulerOnline is not and vice versa. The
amount of schedulers online can be changed at run time via
erlang:system_flag(schedulers_online, SchedulersOnline).
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.