Exec

Description

Executes a system command. When the os attribute is specified, then the command is only executed when Apache Ant is run on one of the specified operating systems.

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 since Ant 1.6, any attempt to read input in the forked program will receive an EOF (-1). This is a change from Ant 1.5, where such an attempt would block.

If you want to execute an executable using a path relative to the project's basedir, you may need to use vmlauncher=false on some operating systems—but even this may fail (Solaris 8/9 has been reported as problematic). The resolveexecutable attribute should be more reliable, as would be something like

<property name="executable-full-path"
          location="../relative/path/to/executable"/>
<exec executable="${executable-full-path}" ...

Windows Users

The <exec> task delegates to Runtime.exec which in turn apparently calls ::CreateProcess. 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 .EXE files are looked for, not .COM, .CMD or other file types listed in the environment variable PATHEXT. That is only used by the shell.

Note that .bat files cannot in general by executed directly. One normally needs to execute the command shell executable cmd using the /c switch.

<target name="help">
  <exec executable="cmd">
    <arg value="/c"/>
    <arg value="ant.bat"/>
    <arg value="-p"/>
  </exec>
</target>

A common problem is not having the executable on the PATH. In case you get an error message Cannot run program "...":CreateProcess error=2. The system cannot find the path specified. have a look at your PATH 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 PATH (set PATH=%PATH%;dirOfProgram) or specify the absolute path in the executable attribute in your buildfile.

Cygwin Users

The <exec> task will not understand paths such as /bin/sh for the executable 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 cygwin1.dll). The only work-around for this is to compile a JVM under Cygwin (at your own risk). See for instance OpenJDK build instructions for cygwin.

OpenVMS Users

The command specified using executable and <arg> elements is executed exactly as specified inside a temporary DCL script. This has some implications:

• the DCL script will be created inside the temporary directory.
• paths have to be written in VMS style
• if your executable points to a DCL script remember to prefix it with an @-sign (e.g. executable=@[FOO]BAR.COM), just as you would in a DCL script

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 JAVA.EXE, use a <java> task with the fork attribute set to true instead as this task will follow the JVM's interpretation of exit codes.

RedHat S/390 Users

It has been reported on linux-390 that shell scripts invoked via the Ant Exec task must have their interpreter specified, i.e., the scripts must start with something like:

#!/bin/bash

or the task will fail as follows:

[exec] Warning: UNIXProcess.forkAndExec native error: Exec format error
[exec] Result: 255

Running Ant as a background process on Unix(-like) systems

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

Parameters

Examples

<exec dir="${src}" executable="cmd.exe" os="Windows 2000" output="dir.txt">
  <arg line="/c dir"/>
</exec>

Parameters specified as nested elements

arg

Command line arguments should be specified as nested <arg> elements. See Command line arguments.

env

It is possible to specify environment variables to pass to the system command via nested <env> elements.

redirector

A nested I/O Redirector 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 <exec> attributes for backwards compatibility. Any file mapping is done using a null sourcefile; therefore not allMapper 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.

Errors and return codes

By default the return code of a <exec> is ignored; when you set failonerror to true then any return code signaling failure (OS specific) causes the build to fail. Alternatively, you can set resultproperty to the name of a property and have it assigned to the result code (barring immutability, of course).

If the attempt to start the program fails with an OS dependent error code, then <exec> halts the build unless failifexecutionfails is set to false. You can use that to run a program if it exists, but otherwise do nothing.

What do those error codes mean? Well, they are OS dependent. On Windows boxes you have to look at the documentation; error=2 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.

Examples

Start emacs on display 1 of the X Window System.

<exec executable="emacs">
  <env key="DISPLAY" value=":1.0"/>
</exec>

Add ${basedir}/bin to the PATH of the system command.

<property environment="env"/>
<exec ... >
  <env key="PATH" path="${env.PATH}:${basedir}/bin"/>
</exec>

Start the ${browser} with the specified ${file} and end the Ant process. The browser will remain.

<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>

Send the string blah before blah to the cat executable, using an <inputfilterchain> to replace before with after on the way in. Output is sent to the file redirector.out and stored in a property of the same name. Similarly, error output is sent to a file and a property, both named redirector.err.

<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>

Note: do not try to specify arguments using a simple arg-element and separate them by spaces. This results in only a single argument containing the entire string.

Timeouts: 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 -1, which will halt the build if failonerror=true, but be ignored otherwise.