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  <header>
    <copyright>
      <year>1997</year><year>2020</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>erlc</title>
    <prepared>Bj&ouml;rn Gustavsson</prepared>
    <responsible>Bjarne D&auml;cker</responsible>
    <docno>1</docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked></checked>
    <date>1997-03-24</date>
    <rev>A</rev>
    <file>erlc.xml</file>
  </header>
  <com>erlc</com>
  <comsummary>Compiler</comsummary>
  <description>
    <p>The <c><![CDATA[erlc]]></c> program provides a common way to run
      all compilers in the Erlang system.
      Depending on the extension of each input file, <c><![CDATA[erlc]]></c>
      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.</p>
    <p>The current working directory, <c>"."</c>, 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
      compiler.</p>
  </description>

  <funcs>
    <func>
      <name>erlc flags file1.ext file2.ext...</name>
      <fsummary>Compile files.</fsummary>
      <desc>
        <p>Compiles one or more files. The files must include the extension,
          for example, <c><![CDATA[.erl]]></c> for Erlang source code, or
          <c><![CDATA[.yrl]]></c> for Yecc source code.
          <c><![CDATA[Erlc]]></c> uses the extension to invoke the correct
          compiler.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Generally Useful Flags</title>
    <p>The following flags are supported:</p>
    <taglist>
      <tag><c>-I &lt;Directory&gt;</c></tag>
      <item>
        <p>Instructs the compiler to search for include files in
          the <c>Directory</c>. When encountering an
          <c><![CDATA[-include]]></c> or <c><![CDATA[-include_lib]]></c>
          directive, the compiler searches for header files in the following
          directories:</p>
        <list type="bulleted">
          <item>
            <p><c><![CDATA["."]]></c>, the current working directory of the
              file server</p>
          </item>
          <item>
            <p>The base name of the compiled file</p>
          </item>
          <item>
            <p>The directories specified using option <c><![CDATA[-I]]></c>;
              the directory specified last is searched first</p>
          </item>
        </list>
      </item>
      <tag><c>-o &lt;Directory&gt;</c></tag>
      <item>
        <p>The directory where the compiler is to place the output files.
          Defaults to the current working directory.</p>
      </item>
      <tag><c>-D&lt;Name&gt;</c></tag>
      <item>
        <p>Defines a macro.</p>
      </item>
      <tag><c>-D&lt;Name&gt;=&lt;Value&gt;</c></tag>
      <item>
        <p>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 all platforms.</p>
      </item>
      <tag><c>-WError</c></tag>
      <item>
        <p>Makes all warnings into errors.</p>
      </item>
      <tag><c>-W&lt;Number&gt;</c></tag>
      <item>
        <p>Sets warning level to <c>Number</c>. Defaults to
          <c><![CDATA[1]]></c>. To turn off warnings,
          use <c><![CDATA[-W0]]></c>.</p>
      </item>
      <tag><c>-W</c></tag>
      <item>
        <p>Same as <c><![CDATA[-W1]]></c>. Default.</p>
      </item>
      <tag><c>-v</c></tag>
      <item>
        <p>Enables verbose output.</p>
      </item>
      <tag><c>-b &lt;Output_type&gt;</c></tag>
      <item>
        <p>Specifies the type of output file.
          <c>Output_type</c> 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.</p>
      </item>
      <tag><c>-smp</c></tag>
      <item>
        <p>Compiles using the SMP emulator. This is mainly useful
          for compiling native code, which must be compiled with the same
          runtime system that it is to be run on.</p>
      </item>
      <tag><c>-no-server</c></tag>
      <item>
        <p>Do not use the
	<seecom marker="#compile_server">compile server</seecom>.</p>
      </item>
      <tag><c>-server</c></tag>
      <item>
        <p>Use the
	<seecom marker="#compile_server">compile server</seecom>.</p>
      </item>
      <tag><c>-M</c></tag>
      <item>
        <p>Produces a Makefile rule to track header dependencies. The
          rule is sent to <c>stdout</c>. No object file is produced.</p>
      </item>

      <tag><c>-MMD</c></tag>
      <item>
        <p>Generate dependencies as a side-effect. The object file
	will be produced as normal. This option overrides the
	option <c><![CDATA[-M]]></c>.</p>
      </item>

      <tag><c>-MF &lt;Makefile&gt;</c></tag>
      <item>
        <p>As option <c><![CDATA[-M]]></c>, except that the
          Makefile is written to <c>Makefile</c>. No object
          file is produced.</p>
      </item>
      <tag><c>-MD</c></tag>
      <item>
        <p>Same as <c><![CDATA[-M -MF <File>.Pbeam]]></c>.</p>
      </item>
      <tag><c>-MT &lt;Target&gt;</c></tag>
      <item>
        <p>In conjunction with option <c><![CDATA[-M]]></c> or
          <c><![CDATA[-MF]]></c>, changes the name of the rule emitted
          to <c>Target</c>.</p>
      </item>
      <tag><c>-MQ &lt;Target&gt;</c></tag>
      <item>
        <p>As option <c><![CDATA[-MT]]></c>, except that characters special to
          <c>make/1</c> are quoted.</p>
      </item>
      <tag><c>-MP</c></tag>
      <item>
        <p>In conjunction with option <c><![CDATA[-M]]></c> or
          <c><![CDATA[-MF]]></c>, adds a phony target for each dependency.</p>
      </item>
      <tag><c>-MG</c></tag>
      <item>
        <p>In conjunction with option <c><![CDATA[-M]]></c> or
          <c><![CDATA[-MF]]></c>, considers missing headers as generated
          files and adds them to the dependencies.</p>
      </item>
      <tag><c>--</c></tag>
      <item>
        <p>Signals that no more options will follow.
          The rest of the arguments is treated as filenames,
          even if they start with hyphens.</p>
      </item>
      <tag><c>+&lt;Term&gt;</c></tag>
      <item>
        <p>A flag starting with a plus (<c>+</c>) rather than a hyphen
          is converted to an Erlang term and passed unchanged to
          the compiler.
          For example, option <c><![CDATA[export_all]]></c> for the Erlang
          compiler can be specified as follows:</p>
        <pre>
erlc +export_all file.erl</pre>
        <p>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 platforms.</p>
      </item>
    </taglist>
  </section>

  <section>
    <title>Special Flags</title>
    <p>The following flags are useful in special situations,
      such as rebuilding the OTP system:</p>
    <taglist>
      <tag><c>-pa &lt;Directory&gt;</c></tag>
      <item>
        <p>Appends <c>Directory</c> to the front of the code path in
          the invoked Erlang emulator.
          This can be used to invoke another
          compiler than the default one.</p>
      </item>
      <tag><c>-pz &lt;Directory&gt;</c></tag>
      <item>
        <p>Appends <c>Directory</c> to the code path in
          the invoked Erlang emulator.</p>
      </item>
    </taglist>
  </section>

  <section>
    <title>Supported Compilers</title>
    <p>The following compilers are supported:</p>
    <taglist>
      <tag><c>.erl</c></tag>
      <item>
        <p>Erlang source code. It generates a <c><![CDATA[.beam]]></c> file.</p>
        <p>Options <c>-P</c>, <c>-E</c>, and <c>-S</c> are equivalent to
          <c>+'P'</c>, <c>+'E'</c>, and <c>+'S'</c>, except that it is not
          necessary to include the single quotes to protect them from the
          shell.</p>
        <p>Supported options: <c>-I</c>, <c>-o</c>, <c>-D</c>, <c>-v</c>,
          <c>-W</c>, <c>-b</c>.</p>
      </item>
      <tag><c>.S</c></tag>
      <item>
        <p>Erlang assembler source code. It generates a <c><![CDATA[.beam]]></c>
          file.</p>
        <p>Supported options: same as for <c>.erl</c>.</p>
      </item>
      <tag><c>.core</c></tag>
      <item>
        <p>Erlang core source code. It generates a <c><![CDATA[.beam]]></c>
          file.</p>
        <p>Supported options: same as for <c>.erl</c>.</p>
      </item>
      <tag><c>.yrl</c></tag>
      <item>
        <p>Yecc source code. It generates an <c><![CDATA[.erl]]></c> file.</p>
        <p>Use option <c>-I</c> with the name of a file to use that file
          as a customized prologue file (option
          <c><![CDATA[includefile]]></c>).</p>
        <p>Supported options: <c>-o</c>, <c>-v</c>, <c>-I</c>, <c>-W</c>.</p>
      </item>
      <tag><c>.mib</c></tag>
      <item>
        <p>MIB for SNMP. It generates a <c><![CDATA[.bin]]></c> file.</p>
        <p>Supported options: <c>-I</c>, <c>-o</c>, <c>-W</c>.</p>
      </item>
      <tag><c>.bin</c></tag>
      <item>
        <p>A compiled MIB for SNMP. It generates a <c><![CDATA[.hrl]]></c>
          file.</p>
        <p>Supported options: <c>-o</c>, <c>-v</c>.</p>
      </item>
      <tag><c>.rel</c></tag>
      <item>
        <p>Script file. It generates a boot file.</p>
        <p>Use option <c>-I</c> to name directories to be searched for
          application files (equivalent to the <c><![CDATA[path]]></c> in the
          option list for <c><![CDATA[systools:make_script/2]]></c>).</p>
        <p>Supported option: <c>-o</c>.</p>
      </item>
      <tag><c>.asn1</c></tag>
      <item>
        <p>ASN1 file. It creates an <c><![CDATA[.erl]]></c>,
          <c><![CDATA[.hrl]]></c>, and <c><![CDATA[.asn1db]]></c> file from
          an <c><![CDATA[.asn1]]></c> file. Also compiles the
          <c><![CDATA[.erl]]></c> using the Erlang compiler unless option
          <c><![CDATA[+noobj]]></c> is specified.</p>
        <p>Supported options: <c>-I</c>, <c>-o</c>, <c>-b</c>, <c>-W</c>.</p>
      </item>
      <tag><c>.idl</c></tag>
      <item>
        <p>IC file. It runs the IDL compiler.</p>
        <p>Supported options: <c>-I</c>, <c>-o</c>.</p>
      </item>
    </taglist>
  </section>

  <section>
    <marker id="compile_server"></marker>
    <title>Compile Server</title>
    <p>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.</p>

    <p>By default, the compile server is not used. It can be
    enabled by giving <c>erlc</c> the option <c>-server</c> or by
    setting the environment variable <c>ERLC_USE_SERVER</c> to
    <c>yes</c> or <c>true</c>.</p>

    <p>When the compile server is enabled, <c>erlc</c> 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.</p>

    <p><c>erlc</c> 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 compile server.</p>

    <p>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:</p>

    <list type="bulleted">
      <item><c>erlc</c> wants to use a different version of Erlang
      than the compile server is using.</item>
      <item><c>erlc</c> wants to use different options for <c>erl</c>
      than the compile server was started with. (A change to code path
      using the option <c>-pa</c> could cause different parse
      transforms to be loaded. To be safe, the compile server will be
      restarted when any <c>erl</c> option is changed.)</item>
      <item>If the current working directory for <c>erlc</c> is
      different from the working directory active when the compile
      server was started, <strong>and</strong> 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
      compile server.)</item>
    </list>
  </section>

    <section>
    <marker id="environment_variables"></marker>
    <title>Environment Variables</title>
    <taglist>
      <tag><c>ERLC_EMULATOR</c></tag>
      <item>The command for starting the emulator. Defaults to <c>erl</c>
        in the same directory as the <c>erlc</c> program itself,
        or, if it does not exist, <c>erl</c> in any of the directories
        specified in environment variable <c>PATH</c>.</item>
      <tag><c>ERLC_USE_SERVER</c></tag>
      <item>Allowed values are <c>yes</c> or <c>true</c> to use the
      <seecom marker="#compile_server">compile
      server</seecom>, and <c>no</c> or <c>false</c> to not use the
      compile server. If other values are given, <c>erlc</c> will
      print a warning message and continue.
      </item>
      <tag><c>ERLC_SERVER_ID</c></tag>
      <item>Tells <c>erlc</c> to identify the
        <seecom marker="#compile_server">compile server</seecom> 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 alpha&shy;numeric,
        and it defaults to being empty.
      </item>
    </taglist>
  </section>

  <section>
    <title>See Also</title>
    <p><seecom marker="erl"><c>erl(1)</c></seecom>,
      <seeerl marker="compiler:compile"><c>compile(3)</c></seeerl>,
      <seeerl marker="parsetools:yecc"><c>yecc(3)</c></seeerl>,
      <seeerl marker="snmp:snmp"><c>snmp(3)</c></seeerl></p>
  </section>
</comref>
