The erlc program provides a common way to run all compilers in the Erlang
system. Depending on the extension of each input file, erlc invokes the
appropriate compiler. Regardless of which compiler is used, the same flags are
used to provide parameters, such as include paths and output directory.
The current working directory, ".", is not
included in the code path when running the compiler. This is to avoid
loading Beam files from the current working directory that could potentially
be in conflict with the compiler or the Erlang/OTP system used by the
erlc flags file1.ext file2.ext...
The following flags are supported:
Compiles one or more files. The files must include the extension,
for example, .erl for Erlang source code, or .yrl for Yecc
source code. Erlc uses the extension to invoke the correct
The following flags are useful in special situations, such as rebuilding the OTP
- -I <Directory>:
- Instructs the compiler to search for include files in the
Directory. When encountering an -include or
-include_lib directive, the compiler searches for header files in
the following directories:
- ".", the current working directory of the file
- The base name of the compiled file
- The directories specified using option -I; the directory specified
last is searched first
- -o <Directory>:
- The directory where the compiler is to place the output files. Defaults to
the current working directory.
- Defines a macro.
- Defines a macro with the specified value. The value can be any Erlang
term. Depending on the platform, the value may need to be quoted if the
shell itself interprets certain characters. On Unix, terms containing
tuples and lists must be quoted. Terms containing spaces must be quoted on
- Makes all warnings into errors.
- Sets warning level to Number. Defaults to 1. To turn off
warnings, use -W0.
- Same as -W1. Default.
- Enables verbose output.
- -b <Output_type>:
- Specifies the type of output file. Output_type is the same as the
file extension of the output file, but without the period. This option is
ignored by compilers that have a single output format.
- Do not use the compile server.
- Use the compile server.
- Produces a Makefile rule to track header dependencies. The rule is sent to
stdout. No object file is produced.
- Generate dependencies as a side-effect. The object file will be produced
as normal. This option overrides the option -M.
- -MF <Makefile>:
- As option -M, except that the Makefile is written to
Makefile. No object file is produced.
- Same as -M -MF <File>.Pbeam.
- -MT <Target>:
- In conjunction with option -M or -MF, changes the name of
the rule emitted to Target.
- -MQ <Target>:
- As option -MT, except that characters special to make/1 are
- In conjunction with option -M or -MF, adds a phony target
for each dependency.
- In conjunction with option -M or -MF, considers missing
headers as generated files and adds them to the dependencies.
- Signals that no more options will follow. The rest of the arguments is
treated as filenames, even if they start with hyphens.
- A flag starting with a plus (+) rather than a hyphen is converted
to an Erlang term and passed unchanged to the compiler. For example,
option export_all for the Erlang compiler can be specified as
erlc +export_all file.erl
Depending on the platform, the value may need to be quoted if the
shell itself interprets certain characters. On Unix, terms containing tuples
and lists must be quoted. Terms containing spaces must be quoted on all
The following compilers are supported:
- -pa <Directory>:
- Appends Directory to the front of the code path in the invoked
Erlang emulator. This can be used to invoke another compiler than the
- -pz <Directory>:
- Appends Directory to the code path in the invoked Erlang
The compile server can be used to potentially speed up the build of multi-file
projects by avoiding to start an Erlang system for each file to compile.
Whether it will speed up the build depends on the nature of the project and
the build machine.
- Erlang source code. It generates a .beam file.
Options -P, -E, and -S are equivalent to
+'P', +'E', and +'S', except that it is not necessary
to include the single quotes to protect them from the shell.
Supported options: -I, -o, -D, -v,
- Erlang assembler source code. It generates a .beam file.
Supported options: same as for .erl.
- Erlang core source code. It generates a .beam file.
Supported options: same as for .erl.
- Yecc source code. It generates an .erl file.
Use option -I with the name of a file to use that file as a
customized prologue file (option includefile).
Supported options: -o, -v, -I, -W.
- MIB for SNMP. It generates a .bin file.
Supported options: -I, -o, -W.
- A compiled MIB for SNMP. It generates a .hrl file.
Supported options: -o, -v.
- Script file. It generates a boot file.
Use option -I to name directories to be searched for
application files (equivalent to the path in the option list for
- ASN1 file. It creates an .erl, .hrl, and .asn1db file
from an .asn1 file. Also compiles the .erl using the Erlang
compiler unless option +noobj is specified.
Supported options: -I, -o, -b, -W.
- IC file. It runs the IDL compiler.
Supported options: -I, -o.
By default, the compile server is not used. It can be enabled by
giving erlc the option -server or by setting the environment
variable ERLC_USE_SERVER to yes or true.
When the compile server is enabled, erlc will automatically
use the server if it is started and start the server if has not already
started. The server will terminate itself when it has been idle for some
number of seconds.
erlc and the compile server communicate using the Erlang
distribution. The compile server is started as a hidden node, with a name
that includes the current user. Thus, each user on a computer has their own
Using the compile server does not always speed up the build, as
the compile server sometimes must be restarted to ensure correctness. Here
are some examples of situtations that force a restart:
- erlc wants to use a different version of Erlang than the compile
server is using.
- erlc wants to use different options for erl than the compile
server was started with. (A change to code path using the option
-pa could cause different parse transforms to be loaded. To be
safe, the compile server will be restarted when any erl option is
- If the current working directory for erlc is different from the
working directory active when the compile server was started, and
if the compile server has active jobs, it will be restarted as soon as
those jobs have finished. (Build systems that build files randomly across
multiple directories in parallel will probably not benefit from the
erl(1), compile(3), yecc(3), snmp(3)
- The command for starting the emulator. Defaults to erl in the same
directory as the erlc program itself, or, if it does not exist,
erl in any of the directories specified in environment variable
- Allowed values are yes or true to use the compile server,
and no or false to not use the compile server. If other
values are given, erlc will print a warning message and
- Tells erlc to identify the compile server by the given name,
allowing a single user to run multiple unrelated builds in parallel
without them affecting each other, which can be useful for shared build
machines and the like. The name must be alphanumeric, and it defaults to
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