manual/Tasks/exec.html - ant - Git at Google

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 <head>
   <link rel="stylesheet" type="text/css" href="../stylesheets/style.css">
   <title>Exec Task</title>
 </head>

 <body>

 <h2 id="exec">Exec</h2>
 <h3>Description</h3>
 <p>Executes a system command. When the <var>os</var> attribute is specified, then the command is
 only executed when Apache Ant is run on one of the specified operating systems.</p>

 <p>Note that you cannot interact with the forked program, the only way to send input to it is via
 the input and inputstring attributes. Also note that <em>since Ant 1.6</em>, any attempt to read
 input in the forked program will receive an EOF (<q>-1</q>). This is a change from Ant 1.5, where
 such an attempt would block.</p>

 <p>If you want to execute an executable using a path relative to the project's <var>basedir</var>,
 you may need to use <var>vmlauncher</var>=<q>false</q> on some operating systems&mdash;but even this
 may fail (Solaris 8/9 has been reported as problematic).  The <var>resolveexecutable</var> attribute
 should be more reliable, as would be something like</p>
 <pre>
 &lt;property name="executable-full-path"
           location="../relative/path/to/executable"/&gt;
 &lt;exec executable="${executable-full-path}" ...</pre>

 <h4>Windows Users</h4>
 <p>The <code>&lt;exec&gt;</code> task delegates to <code>Runtime.exec</code> which in turn
 apparently
 calls <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx"
 target="_top"><code>::CreateProcess</code></a>. It is the latter Win32 function that defines the
 exact semantics of the call. In particular, if you do not put a file extension on the executable,
 only <samp>.EXE</samp> files are looked for, not <samp>.COM</samp>, <samp>.CMD</samp> or other file
 types listed in the environment variable <code>PATHEXT</code>. That is only used by the shell.</p>
 <p>Note that <samp>.bat</samp> files cannot in general by executed directly.  One normally needs to
 execute the command shell executable <kbd>cmd</kbd> using the <kbd>/c</kbd> switch.</p>
 <pre>
 &lt;target name="help"&gt;
   &lt;exec executable="cmd"&gt;
     &lt;arg value="/c"/&gt;
     &lt;arg value="ant.bat"/&gt;
     &lt;arg value="-p"/&gt;
   &lt;/exec&gt;
 &lt;/target&gt;</pre>

 <p>A common problem is not having the executable on the <code>PATH</code>. In case you get an error
 message <code class="output">Cannot run program "...":CreateProcess error=2. The system cannot find
 the path specified.</code> have a look at your <code>PATH</code> variable. Just type the command
 directly on the command line and if Windows finds it, Ant should do it too. (Otherwise ask on the
 user mailinglist for help.) If Windows can not execute the program, add the directory of the program
 to the <code>PATH</code> (<code>set PATH=%PATH%;dirOfProgram</code>) or specify the absolute path in
 the <var>executable</var> attribute in your buildfile.</p>

 <h4>Cygwin Users</h4>
 <p>The <code>&lt;exec&gt;</code> task will not understand paths such as <q>/bin/sh</q> for
 the <var>executable</var> parameter.  This is because JVM in which Ant is running is a standard
 Windows executable and is not aware of the Cygwin environment (i.e., doesn't
 load <samp>cygwin1.dll</samp>).  The only work-around for this is to compile a JVM under Cygwin (at
 your own risk).  See for
 instance <a href="https://cdn.rawgit.com/AdoptOpenJDK/openjdk-jdk9/dev/common/doc/building.html#cygwin"
 target="_top">OpenJDK build instructions for cygwin</a>.</p>

 <h4>OpenVMS Users</h4>
 <p>The command specified using <var>executable</var> and <code>&lt;arg&gt;</code> elements is
 executed exactly as specified inside a temporary DCL script.  This has some implications:</p>
 <ul>
   <li>the DCL script will be created inside
   the <a href="../running.html#tmpdir">temporary directory</a>.</li>
   <li>paths have to be written in VMS style</li>
   <li>if your <var>executable</var> points to a DCL script remember to prefix it with
     an <q>@</q>-sign (e.g. <var>executable</var>=<q>@[FOO]BAR.COM</q>), just as you would in a DCL
     script</li>
 </ul>

 <p>Please note that JVM provided by HP doesn't follow OpenVMS' conventions of exit codes.  If you
 run a JVM with this task, the task may falsely claim that an error occurred (or silently ignore an
 error).  Don't use this task to run <kbd>JAVA.EXE</kbd>, use a <code>&lt;java&gt;</code> task with
 the <var>fork</var> attribute set to <q>true</q> instead as this task will follow the JVM's
 interpretation of exit codes.</p>

 <h4>RedHat S/390 Users</h4>
 <p>It has been <a href="https://www.mail-archive.com/linux-390@vm.marist.edu/msg22223.html"
 target="_top">reported on linux-390</a> that shell scripts invoked via the Ant Exec task must have
 their interpreter specified, i.e., the scripts must start with something like:</p>

 <pre>#!/bin/bash</pre>
 <p>or the task will fail as follows:</p>
 <pre class="output">
 [exec] Warning: UNIXProcess.forkAndExec native error: Exec format error
 [exec] Result: 255</pre>

 <h4 id="background">Running Ant as a background process on Unix(-like) systems</h4>

 <p>If you run Ant as a background process (like <kbd>ant &amp;</kbd>) and use
 the <code>&lt;exec&gt;</code> task with <var>spawn</var> set to <q>false</q>, you must provide
 explicit input to the forked process or Ant will be suspended because it tries to read from the
 standard input.</p>

 <h3>Parameters</h3>
 <table class="attr">
   <tr>
     <th scope="col">Attribute</th>
     <th scope="col">Description</th>
     <th scope="col">Required</th>
   </tr>
   <tr>
     <td>command</td>
     <td>the command to execute with all command line arguments. <em><u>Deprecated</u>,
       use <var>executable</var> and nested <code>&lt;arg&gt;</code> elements instead</em>.</td>
     <td rowspan="2">Exactly one of the two</td>
   </tr>
   <tr>
     <td>executable</td>
     <td class="left">the command to execute without any command line arguments.</td>
   </tr>
   <tr>
     <td>dir</td>
     <td>the directory in which the command should be executed.</td>
     <td>No; if <var>vmlauncher</var> is <q>true</q>, defaults to the current working directory,
       otherwise the project's <var>basedir</var></td>
   </tr>
   <tr>
     <td>os</td>
     <td>list of Operating Systems on which the command may be executed. If the current OS's name is
       contained in this list, the command will be executed. The OS's name is determined by JVM and
       is set in the <code>os.name</code> system property.
       </td>
     <td>No</td>
   </tr>
   <tr>
     <td>osfamily</td>
     <td>OS family as used in the <code>&lt;os&gt;</code> condition.  <em>since Ant 1.7</em></td>
     <td>No</td>
   </tr>
   <tr>
     <td>spawn</td>
     <td>whether or not you want the command to be spawned<br/>If you spawn a command, its output
     will not be logged by Ant.<br/>The <var>input</var>, <var>output</var>, <var>error</var>,
     and <var>result</var> property settings are not active when spawning a process.<br/><em>since
     Ant 1.6</em>
     </td>
     <td>No; default is <q>false</q></td>
   </tr>
   <tr>
     <td>output</td>
     <td>Name of a file to which to write the output. If the error stream is not also redirected to a
       file or property, it will appear in this output.</td>
     <td>No</td>
   </tr>
   <tr>
     <td>error</td>
     <td>The file to which the standard error of the command should be redirected.  <em>since Ant
     1.6</em></td>
     <td>No</td>
   </tr>
   <tr>
     <td>logError</td>
     <td>This attribute is used when you wish to see error output in Ant's log and you are
       redirecting output to a file/property. The error output will not be included in the output
       file/property. If you redirect error with the <var>error</var> or <var>errorProperty</var>
       attributes, this will have no effect.  <em>since Ant 1.6</em></td>
     <td>No</td>
   </tr>
   <tr>
     <td>append</td>
     <td>Whether output and error files should be appended to or overwritten.</td>
     <td>No; defaults to <q>false</q></td>
   </tr>
   <tr>
     <td>outputproperty</td>
     <td>The name of a property in which the output of the command should be stored. Unless the error
       stream is redirected to a separate file or stream, this property will include the error
       output.</td>
     <td>No</td>
   </tr>
   <tr>
     <td>errorproperty</td>
     <td>The name of a property in which the standard error of the command should be
       stored.  <em>since Ant 1.6</em></td>
     <td>No</td>
   </tr>
   <tr>
     <td>input</td>
     <td>A file from which the executed command's standard input is taken. This attribute is mutually
       exclusive with the <var>inputstring</var> attribute.  <em>since Ant 1.6</em></td>
     <td>No</td>
   </tr>
   <tr>
     <td>inputstring</td>
     <td>A string which serves as the input stream for the executed command. This attribute is
       mutually exclusive with the <var>input</var> attribute.  <em>since Ant 1.6</em></td>
     <td>No</td>
   </tr>
   <tr>
     <td>resultproperty</td>
     <td>the name of a property in which the return code of the command should be stored. Only of
       interest if <var>failonerror</var>=<q>false</q>.</td>
     <td>No</td>
   </tr>
   <tr>
     <td>timeout</td>
     <td>Stop the command if it doesn't finish within the specified time (given in
       milliseconds).</td>
     <td>No</td>
   </tr>
   <tr>
     <td>failonerror</td>
     <td>Stop the build process if the command exits with a return code signaling failure.</td>
     <td>No; defaults to <q>false</q></td>
   </tr>
   <tr>
     <td>failifexecutionfails</td>
     <td>Stop the build if we can't start the program.</td>
     <td>No; defaults to <q>true</q></td>
   </tr>
   <tr>
     <td>newenvironment</td>
     <td>Do not propagate old environment when new environment variables are specified.</td>
     <td>No; default is <q>false</q></td>
   </tr>
   <tr>
     <td>vmlauncher</td>
     <td>Run command using the JVM's execution facilities where available. If set to <q>false</q> the
       underlying OS's shell, either directly or through the <kbd>antRun</kbd> scripts, will be
       used.  Under some operating systems, this gives access to facilities not normally available
       through JVM including, under Windows, being able to execute scripts, rather than their
       associated interpreter.  If you want to specify the name of the executable as a relative path
       to the directory given by the <var>dir</var> attribute, it may become necessary to
       set <var>vmlauncher</var> to <q>false</q> as well.</td>
     <td>No; default is <q>true</q></td>
   </tr>
   <tr>
     <td>resolveexecutable</td>
     <td>When this attribute is <q>true</q>, the name of the executable is resolved firstly against
       the project <var>basedir</var> and if that does not exist, against the execution directory if
       specified. On Unix systems, if you only want to allow execution of commands in the user's
       path, set this to <q>false</q>.  <em>since Ant 1.6</em></td>
     <td>No; default is <q>false</q></td>
   </tr>
   <tr>
     <td>searchpath</td>
     <td>When this attribute is <q>true</q>, then system path environment variables will be searched
       when resolving the location of the executable. <em>since Ant 1.6.3</em></td>
     <td>No; default is <q>false</q></td>
   </tr>
   <tr>
     <td>discardOutput</td>
     <td>Whether output should completely be discarded. This setting is
       incompatible with any setting that redirects output to files or
       properties.<br/>
       If you set this to <q>true</q> error output will be discared as
       well unless you redirect error output to files, properties or
       enable <q>logError</q>.
       <em>Since Ant 1.10.10</em>
     </td>
     <td>No; defaults to <q>false</q></td>
   </tr>
   <tr>
     <td>discardError</td>
     <td>Whether error output should completely be discarded. This
       setting is incompatible with any setting that redirects error
       output to files or properties as well as <q>logError</q>.
       <em>Since Ant 1.10.10</em>
     </td>
     <td>No; defaults to <q>false</q></td>
   </tr>
 </table>
 <h3>Examples</h3>
 <pre>
 &lt;exec dir=&quot;${src}&quot; executable=&quot;cmd.exe&quot; os=&quot;Windows 2000&quot; output=&quot;dir.txt&quot;&gt;
   &lt;arg line=&quot;/c dir&quot;/&gt;
 &lt;/exec&gt;</pre>

 <h3>Parameters specified as nested elements</h3>
 <h4>arg</h4>
 <p>Command line arguments should be specified as nested <code>&lt;arg&gt;</code>
 elements. See <a href="../using.html#arg">Command line arguments</a>.</p>
 <h4 id="env">env</h4>
 <p>It is possible to specify environment variables to pass to the system command via
 nested <code>&lt;env&gt;</code> elements.</p>
 <table class="attr">
   <tr>
     <th scope="col">Attribute</th>
     <th scope="col">Description</th>
     <th scope="col">Required</th>
   </tr>
   <tr>
     <td>key</td>
     <td>The name of the environment variable.<br/><strong>Note</strong>: <em>since Ant 1.7</em>, for
       Windows, the name is case-insensitive.</td>
     <td>Yes</td>
   </tr>
   <tr>
     <td>value</td>
     <td>The literal value for the environment variable.</td>
     <td rowspan="3">Exactly one of these</td>
   </tr>
   <tr>
     <td>path</td>
     <td class="left">The value for a <code>PATH</code>-like environment variable. You can
       use <q>;</q> or <q>:</q> as path separators and Ant will convert it to the platform's local
       conventions.</td>
   </tr>
   <tr>
     <td>file</td>
     <td class="left">The value for the environment variable. Will be replaced by the absolute
       filename of the file by Ant.</td>
   </tr>
 </table>
 <h4 id="redirector">redirector</h4>
 <em>Since Ant 1.6.2</em>
 <p>A nested <a href="../Types/redirector.html">I/O Redirector</a> can be specified.  In general, the
 attributes of the redirector behave as the corresponding attributes available at the task level.
 The most notable peculiarity stems from the retention of the <code>&lt;exec&gt;</code> attributes
 for backwards compatibility.  Any file mapping is done using a <code>null</code> sourcefile;
 therefore not all<a href="../Types/mapper.html">Mapper</a> types will return results.  When no
 results are returned, redirection specifications will fall back to the task level attributes.  In
 practice this means that defaults can be specified for input, output, and error output files.</p>
 <h3>Errors and return codes</h3>
 <p>By default the return code of a <code>&lt;exec&gt;</code> is ignored; when you
 set <var>failonerror</var> to <q>true</q> then any return code signaling failure (OS specific)
 causes the build to fail. Alternatively, you can set <var>resultproperty</var> to the name of a
 property and have it assigned to the result code (barring immutability, of course).</p>
 <p>If the attempt to start the program fails with an OS dependent error code,
 then <code>&lt;exec&gt;</code> halts the build unless <var>failifexecutionfails</var> is set
 to <q>false</q>. You can use that to run a program if it exists, but otherwise do nothing.</p>
 <p>What do those error codes mean? Well, they are OS dependent. On Windows boxes you have to look
 at <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx"
 target="_top">the documentation</a>; <code>error=2</code> means 'no such program', which usually
 means it is not on the path. Any time you see such an error from any Ant task, it is usually not an
 Ant bug, but some configuration problem on your machine.</p>

 <h3>Examples</h3>

 <p>Start <kbd>emacs</kbd> on display 1 of the X Window System.</p>
 <pre>
 &lt;exec executable=&quot;emacs&quot;&gt;
   &lt;env key=&quot;DISPLAY&quot; value=&quot;:1.0&quot;/&gt;
 &lt;/exec&gt;
 </pre>

 <p>Add <samp>${basedir}/bin</samp> to the <code>PATH</code> of the system command.</p>
 <pre>
 &lt;property environment=&quot;env&quot;/&gt;
 &lt;exec ... &gt;
   &lt;env key=&quot;PATH&quot; path=&quot;${env.PATH}:${basedir}/bin&quot;/&gt;
 &lt;/exec&gt;
 </pre>

 <p>Start the <samp>${browser}</samp> with the specified <samp>${file}</samp> and end the Ant
 process. The browser will remain.</p>
 <pre>
 &lt;property name="browser" location="C:/Program Files/Internet Explorer/iexplore.exe"/&gt;
 &lt;property name="file" location="ant/docs/manual/index.html"/&gt;

 &lt;exec executable="${browser}" spawn="true"&gt;
     &lt;arg value="${file}"/&gt;
 &lt;/exec&gt;
 </pre>

 <p>Send the string <q>blah before blah</q> to the <kbd>cat</kbd> executable, using
 an <a href="../Types/filterchain.html">&lt;inputfilterchain&gt;</a> to replace <q>before</q>
 with <q>after</q> on the way in. Output is sent to the file <samp>redirector.out</samp> and stored
 in a property of the same name. Similarly, error output is sent to a file and a property, both
 named <samp>redirector.err</samp>.</p>
 <pre>
 &lt;exec executable=&quot;cat&quot;&gt;
     &lt;redirector outputproperty=&quot;redirector.out&quot;
                 errorproperty=&quot;redirector.err&quot;
                 inputstring=&quot;blah before blah&quot;&gt;
         &lt;inputfilterchain&gt;
             &lt;replacestring from=&quot;before&quot; to=&quot;after&quot;/&gt;
         &lt;/inputfilterchain&gt;
         &lt;outputmapper type=&quot;merge&quot; to=&quot;redirector.out&quot;/&gt;
         &lt;errormapper type=&quot;merge&quot; to=&quot;redirector.err&quot;/&gt;
     &lt;/redirector&gt;
 &lt;/exec&gt;
 </pre>

 <p><strong>Note</strong>: do not try to specify arguments using a simple <code>arg</code>-element
 and separate them by spaces. This results in only a single argument containing the entire
 string.</p>
 <p><strong>Timeouts</strong>: If a timeout is specified, when it is reached the sub process is
 killed and a message printed to the log. The return value of the execution will be <q>-1</q>, which
 will halt the build if <var>failonerror</var>=<q>true</q>, but be ignored otherwise.</p>
 </body>
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	<head>
	<link rel="stylesheet" type="text/css" href="../stylesheets/style.css">
	<title>Exec Task</title>
	</head>

	<body>

	<h2 id="exec">Exec</h2>
	<h3>Description</h3>
	<p>Executes a system command. When the <var>os</var> attribute is specified, then the command is
	only executed when Apache Ant is run on one of the specified operating systems.</p>

	<p>Note that you cannot interact with the forked program, the only way to send input to it is via
	the input and inputstring attributes. Also note that <em>since Ant 1.6</em>, any attempt to read
	input in the forked program will receive an EOF (<q>-1</q>). This is a change from Ant 1.5, where
	such an attempt would block.</p>

	<p>If you want to execute an executable using a path relative to the project's <var>basedir</var>,
	you may need to use <var>vmlauncher</var>=<q>false</q> on some operating systems—but even this
	may fail (Solaris 8/9 has been reported as problematic). The <var>resolveexecutable</var> attribute
	should be more reliable, as would be something like</p>
	<pre>
	<property name="executable-full-path"
	location="../relative/path/to/executable"/>
	<exec executable="${executable-full-path}" ...</pre>

	<h4>Windows Users</h4>
	<p>The <code><exec></code> task delegates to <code>Runtime.exec</code> which in turn
	apparently
	calls <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx"
	target="_top"><code>::CreateProcess</code></a>. It is the latter Win32 function that defines the
	exact semantics of the call. In particular, if you do not put a file extension on the executable,
	only <samp>.EXE</samp> files are looked for, not <samp>.COM</samp>, <samp>.CMD</samp> or other file
	types listed in the environment variable <code>PATHEXT</code>. That is only used by the shell.</p>
	<p>Note that <samp>.bat</samp> files cannot in general by executed directly. One normally needs to
	execute the command shell executable <kbd>cmd</kbd> using the <kbd>/c</kbd> switch.</p>
	<pre>
	<target name="help">
	<exec executable="cmd">
	<arg value="/c"/>
	<arg value="ant.bat"/>
	<arg value="-p"/>
	</exec>
	</target></pre>

	<p>A common problem is not having the executable on the <code>PATH</code>. In case you get an error
	message <code class="output">Cannot run program "...":CreateProcess error=2. The system cannot find
	the path specified.</code> have a look at your <code>PATH</code> variable. Just type the command
	directly on the command line and if Windows finds it, Ant should do it too. (Otherwise ask on the
	user mailinglist for help.) If Windows can not execute the program, add the directory of the program
	to the <code>PATH</code> (<code>set PATH=%PATH%;dirOfProgram</code>) or specify the absolute path in
	the <var>executable</var> attribute in your buildfile.</p>

	<h4>Cygwin Users</h4>
	<p>The <code><exec></code> task will not understand paths such as <q>/bin/sh</q> for
	the <var>executable</var> parameter. This is because JVM in which Ant is running is a standard
	Windows executable and is not aware of the Cygwin environment (i.e., doesn't
	load <samp>cygwin1.dll</samp>). The only work-around for this is to compile a JVM under Cygwin (at
	your own risk). See for
	instance <a href="https://cdn.rawgit.com/AdoptOpenJDK/openjdk-jdk9/dev/common/doc/building.html#cygwin"
	target="_top">OpenJDK build instructions for cygwin</a>.</p>

	<h4>OpenVMS Users</h4>
	<p>The command specified using <var>executable</var> and <code><arg></code> elements is
	executed exactly as specified inside a temporary DCL script. This has some implications:</p>
	<ul>
	<li>the DCL script will be created inside
	the <a href="../running.html#tmpdir">temporary directory</a>.</li>
	<li>paths have to be written in VMS style</li>
	<li>if your <var>executable</var> points to a DCL script remember to prefix it with
	an <q>@</q>-sign (e.g. <var>executable</var>=<q>@[FOO]BAR.COM</q>), just as you would in a DCL
	script</li>
	</ul>

	<p>Please note that JVM provided by HP doesn't follow OpenVMS' conventions of exit codes. If you
	run a JVM with this task, the task may falsely claim that an error occurred (or silently ignore an
	error). Don't use this task to run <kbd>JAVA.EXE</kbd>, use a <code><java></code> task with
	the <var>fork</var> attribute set to <q>true</q> instead as this task will follow the JVM's
	interpretation of exit codes.</p>

	<h4>RedHat S/390 Users</h4>
	<p>It has been <a href="https://www.mail-archive.com/linux-390@vm.marist.edu/msg22223.html"
	target="_top">reported on linux-390</a> that shell scripts invoked via the Ant Exec task must have
	their interpreter specified, i.e., the scripts must start with something like:</p>

	<pre>#!/bin/bash</pre>
	<p>or the task will fail as follows:</p>
	<pre class="output">
	[exec] Warning: UNIXProcess.forkAndExec native error: Exec format error
	[exec] Result: 255</pre>

	<h4 id="background">Running Ant as a background process on Unix(-like) systems</h4>

	<p>If you run Ant as a background process (like <kbd>ant &</kbd>) and use
	the <code><exec></code> task with <var>spawn</var> set to <q>false</q>, you must provide
	explicit input to the forked process or Ant will be suspended because it tries to read from the
	standard input.</p>

	<h3>Parameters</h3>
	<table class="attr">
	<tr>
	<th scope="col">Attribute</th>
	<th scope="col">Description</th>
	<th scope="col">Required</th>
	</tr>
	<tr>
	<td>command</td>
	<td>the command to execute with all command line arguments. <em><u>Deprecated</u>,
	use <var>executable</var> and nested <code><arg></code> elements instead</em>.</td>
	<td rowspan="2">Exactly one of the two</td>
	</tr>
	<tr>
	<td>executable</td>
	<td class="left">the command to execute without any command line arguments.</td>
	</tr>
	<tr>
	<td>dir</td>
	<td>the directory in which the command should be executed.</td>
	<td>No; if <var>vmlauncher</var> is <q>true</q>, defaults to the current working directory,
	otherwise the project's <var>basedir</var></td>
	</tr>
	<tr>
	<td>os</td>
	<td>list of Operating Systems on which the command may be executed. If the current OS's name is
	contained in this list, the command will be executed. The OS's name is determined by JVM and
	is set in the <code>os.name</code> system property.
	</td>
	<td>No</td>
	</tr>
	<tr>
	<td>osfamily</td>
	<td>OS family as used in the <code><os></code> condition. <em>since Ant 1.7</em></td>
	<td>No</td>
	</tr>
	<tr>
	<td>spawn</td>
	<td>whether or not you want the command to be spawned<br/>If you spawn a command, its output
	will not be logged by Ant.<br/>The <var>input</var>, <var>output</var>, <var>error</var>,
	and <var>result</var> property settings are not active when spawning a process.<br/><em>since
	Ant 1.6</em>
	</td>
	<td>No; default is <q>false</q></td>
	</tr>
	<tr>
	<td>output</td>
	<td>Name of a file to which to write the output. If the error stream is not also redirected to a
	file or property, it will appear in this output.</td>
	<td>No</td>
	</tr>
	<tr>
	<td>error</td>
	<td>The file to which the standard error of the command should be redirected. <em>since Ant
	1.6</em></td>
	<td>No</td>
	</tr>
	<tr>
	<td>logError</td>
	<td>This attribute is used when you wish to see error output in Ant's log and you are
	redirecting output to a file/property. The error output will not be included in the output
	file/property. If you redirect error with the <var>error</var> or <var>errorProperty</var>
	attributes, this will have no effect. <em>since Ant 1.6</em></td>
	<td>No</td>
	</tr>
	<tr>
	<td>append</td>
	<td>Whether output and error files should be appended to or overwritten.</td>
	<td>No; defaults to <q>false</q></td>
	</tr>
	<tr>
	<td>outputproperty</td>
	<td>The name of a property in which the output of the command should be stored. Unless the error
	stream is redirected to a separate file or stream, this property will include the error
	output.</td>
	<td>No</td>
	</tr>
	<tr>
	<td>errorproperty</td>
	<td>The name of a property in which the standard error of the command should be
	stored. <em>since Ant 1.6</em></td>
	<td>No</td>
	</tr>
	<tr>
	<td>input</td>
	<td>A file from which the executed command's standard input is taken. This attribute is mutually
	exclusive with the <var>inputstring</var> attribute. <em>since Ant 1.6</em></td>
	<td>No</td>
	</tr>
	<tr>
	<td>inputstring</td>
	<td>A string which serves as the input stream for the executed command. This attribute is
	mutually exclusive with the <var>input</var> attribute. <em>since Ant 1.6</em></td>
	<td>No</td>
	</tr>
	<tr>
	<td>resultproperty</td>
	<td>the name of a property in which the return code of the command should be stored. Only of
	interest if <var>failonerror</var>=<q>false</q>.</td>
	<td>No</td>
	</tr>
	<tr>
	<td>timeout</td>
	<td>Stop the command if it doesn't finish within the specified time (given in
	milliseconds).</td>
	<td>No</td>
	</tr>
	<tr>
	<td>failonerror</td>
	<td>Stop the build process if the command exits with a return code signaling failure.</td>
	<td>No; defaults to <q>false</q></td>
	</tr>
	<tr>
	<td>failifexecutionfails</td>
	<td>Stop the build if we can't start the program.</td>
	<td>No; defaults to <q>true</q></td>
	</tr>
	<tr>
	<td>newenvironment</td>
	<td>Do not propagate old environment when new environment variables are specified.</td>
	<td>No; default is <q>false</q></td>
	</tr>
	<tr>
	<td>vmlauncher</td>
	<td>Run command using the JVM's execution facilities where available. If set to <q>false</q> the
	underlying OS's shell, either directly or through the <kbd>antRun</kbd> scripts, will be
	used. Under some operating systems, this gives access to facilities not normally available
	through JVM including, under Windows, being able to execute scripts, rather than their
	associated interpreter. If you want to specify the name of the executable as a relative path
	to the directory given by the <var>dir</var> attribute, it may become necessary to
	set <var>vmlauncher</var> to <q>false</q> as well.</td>
	<td>No; default is <q>true</q></td>
	</tr>
	<tr>
	<td>resolveexecutable</td>
	<td>When this attribute is <q>true</q>, the name of the executable is resolved firstly against
	the project <var>basedir</var> and if that does not exist, against the execution directory if
	specified. On Unix systems, if you only want to allow execution of commands in the user's
	path, set this to <q>false</q>. <em>since Ant 1.6</em></td>
	<td>No; default is <q>false</q></td>
	</tr>
	<tr>
	<td>searchpath</td>
	<td>When this attribute is <q>true</q>, then system path environment variables will be searched
	when resolving the location of the executable. <em>since Ant 1.6.3</em></td>
	<td>No; default is <q>false</q></td>
	</tr>
	<tr>
	<td>discardOutput</td>
	<td>Whether output should completely be discarded. This setting is
	incompatible with any setting that redirects output to files or
	properties.<br/>
	If you set this to <q>true</q> error output will be discared as
	well unless you redirect error output to files, properties or
	enable <q>logError</q>.
	<em>Since Ant 1.10.10</em>
	</td>
	<td>No; defaults to <q>false</q></td>
	</tr>
	<tr>
	<td>discardError</td>
	<td>Whether error output should completely be discarded. This
	setting is incompatible with any setting that redirects error
	output to files or properties as well as <q>logError</q>.
	<em>Since Ant 1.10.10</em>
	</td>
	<td>No; defaults to <q>false</q></td>
	</tr>
	</table>
	<h3>Examples</h3>
	<pre>
	<exec dir="${src}" executable="cmd.exe" os="Windows 2000" output="dir.txt">
	<arg line="/c dir"/>
	</exec></pre>

	<h3>Parameters specified as nested elements</h3>
	<h4>arg</h4>
	<p>Command line arguments should be specified as nested <code><arg></code>
	elements. See <a href="../using.html#arg">Command line arguments</a>.</p>
	<h4 id="env">env</h4>
	<p>It is possible to specify environment variables to pass to the system command via
	nested <code><env></code> elements.</p>
	<table class="attr">
	<tr>
	<th scope="col">Attribute</th>
	<th scope="col">Description</th>
	<th scope="col">Required</th>
	</tr>
	<tr>
	<td>key</td>
	<td>The name of the environment variable.<br/><strong>Note</strong>: <em>since Ant 1.7</em>, for
	Windows, the name is case-insensitive.</td>
	<td>Yes</td>
	</tr>
	<tr>
	<td>value</td>
	<td>The literal value for the environment variable.</td>
	<td rowspan="3">Exactly one of these</td>
	</tr>
	<tr>
	<td>path</td>
	<td class="left">The value for a <code>PATH</code>-like environment variable. You can
	use <q>;</q> or <q>:</q> as path separators and Ant will convert it to the platform's local
	conventions.</td>
	</tr>
	<tr>
	<td>file</td>
	<td class="left">The value for the environment variable. Will be replaced by the absolute
	filename of the file by Ant.</td>
	</tr>
	</table>
	<h4 id="redirector">redirector</h4>
	<em>Since Ant 1.6.2</em>
	<p>A nested <a href="../Types/redirector.html">I/O Redirector</a> can be specified. In general, the
	attributes of the redirector behave as the corresponding attributes available at the task level.
	The most notable peculiarity stems from the retention of the <code><exec></code> attributes
	for backwards compatibility. Any file mapping is done using a <code>null</code> sourcefile;
	therefore not all<a href="../Types/mapper.html">Mapper</a> types will return results. When no
	results are returned, redirection specifications will fall back to the task level attributes. In
	practice this means that defaults can be specified for input, output, and error output files.</p>
	<h3>Errors and return codes</h3>
	<p>By default the return code of a <code><exec></code> is ignored; when you
	set <var>failonerror</var> to <q>true</q> then any return code signaling failure (OS specific)
	causes the build to fail. Alternatively, you can set <var>resultproperty</var> to the name of a
	property and have it assigned to the result code (barring immutability, of course).</p>
	<p>If the attempt to start the program fails with an OS dependent error code,
	then <code><exec></code> halts the build unless <var>failifexecutionfails</var> is set
	to <q>false</q>. You can use that to run a program if it exists, but otherwise do nothing.</p>
	<p>What do those error codes mean? Well, they are OS dependent. On Windows boxes you have to look
	at <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx"
	target="_top">the documentation</a>; <code>error=2</code> means 'no such program', which usually
	means it is not on the path. Any time you see such an error from any Ant task, it is usually not an
	Ant bug, but some configuration problem on your machine.</p>

	<h3>Examples</h3>

	<p>Start <kbd>emacs</kbd> on display 1 of the X Window System.</p>
	<pre>
	<exec executable="emacs">
	<env key="DISPLAY" value=":1.0"/>
	</exec>
	</pre>

	<p>Add <samp>${basedir}/bin</samp> to the <code>PATH</code> of the system command.</p>
	<pre>
	<property environment="env"/>
	<exec ... >
	<env key="PATH" path="${env.PATH}:${basedir}/bin"/>
	</exec>
	</pre>

	<p>Start the <samp>${browser}</samp> with the specified <samp>${file}</samp> and end the Ant
	process. The browser will remain.</p>
	<pre>
	<property name="browser" location="C:/Program Files/Internet Explorer/iexplore.exe"/>
	<property name="file" location="ant/docs/manual/index.html"/>

	<exec executable="${browser}" spawn="true">
	<arg value="${file}"/>
	</exec>
	</pre>

	<p>Send the string <q>blah before blah</q> to the <kbd>cat</kbd> executable, using
	an <a href="../Types/filterchain.html"><inputfilterchain></a> to replace <q>before</q>
	with <q>after</q> on the way in. Output is sent to the file <samp>redirector.out</samp> and stored
	in a property of the same name. Similarly, error output is sent to a file and a property, both
	named <samp>redirector.err</samp>.</p>
	<pre>
	<exec executable="cat">
	<redirector outputproperty="redirector.out"
	errorproperty="redirector.err"
	inputstring="blah before blah">
	<inputfilterchain>
	<replacestring from="before" to="after"/>
	</inputfilterchain>
	<outputmapper type="merge" to="redirector.out"/>
	<errormapper type="merge" to="redirector.err"/>
	</redirector>
	</exec>
	</pre>

	<p><strong>Note</strong>: do not try to specify arguments using a simple <code>arg</code>-element
	and separate them by spaces. This results in only a single argument containing the entire
	string.</p>
	<p><strong>Timeouts</strong>: If a timeout is specified, when it is reached the sub process is
	killed and a message printed to the log. The return value of the execution will be <q>-1</q>, which
	will halt the build if <var>failonerror</var>=<q>true</q>, but be ignored otherwise.</p>
	</body>
	</html>