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}" ...
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.
The <exec> task will not understand paths such as /bin/sh
for the executable parameter. This is because the Java VM 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.
The command specified using executable and
<arg> elements is executed exactly as specified
inside a temporary DCL script. This has some implications:
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<exec> to work in an environment with a Java VM
older than version 1.4.1-2 it is also required that the logical
JAVA$FORK_SUPPORT_CHDIR is set to TRUE in
the job table (see the JDK Release Notes).
Please note that the Java VM provided by HP doesn't follow OpenVMS'
conventions of exit codes. If you run a Java VM 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 VM's
interpretation of exit codes.
It has been reported on the VMESA-LISTSERV that shell scripts invoked via the Ant Exec task must have their interpreter specified, i.e., the scripts must start with something like:
or the task will fail as follows:#!/bin/bash
[exec] Warning: UNIXProcess.forkAndExec native error: Exec format error [exec] Result: 255
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.
| Attribute | Description | Required |
| command | the command to execute with all command line
arguments. deprecated, use executable and nested
<arg> elements instead. |
Exactly one of the two. |
| executable | the command to execute without any command line arguments. | |
| dir | the directory in which the command should be executed. | No |
| os | 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 the Java Virtual machine and is set in the "os.name" system property. | No |
| osfamily | OS family as used in the <os> condition. since Ant 1.7 | No |
| spawn | whether or not you want the command to be spawned Default is false. If you spawn a command, its output will not be logged by ant. The input, output, error, and result property settings are not active when spawning a process. since Ant 1.6 |
No |
| output | 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. | No |
| error | The file to which the standard error of the command should be redirected. since Ant 1.6 | No |
| logError | 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 "error" or "errorProperty" attributes, this will have no effect. since Ant 1.6 | No |
| append | Whether output and error files should be appended to or overwritten. Defaults to false. | No |
| outputproperty | 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. | No |
| errorproperty | The name of a property in which the standard error of the command should be stored. since Ant 1.6 | No |
| input | A file from which the executed command's standard input is taken. This attribute is mutually exclusive with the inputstring attribute. since Ant 1.6 | No |
| inputstring | A string which serves as the input stream for the executed command. This attribute is mutually exclusive with the input attribute. since Ant 1.6 | No |
| resultproperty | the name of a property in which the return code of the command should be stored. Only of interest if failonerror=false. | No |
| timeout | Stop the command if it doesn't finish within the specified time (given in milliseconds). | No |
| failonerror | Stop the buildprocess if the command exits with a return code signaling failure. Defaults to false. | No |
| failifexecutionfails | Stop the build if we can't start the program. Defaults to true. | No |
| newenvironment | Do not propagate old environment when new environment variables are specified. | No, default is false |
| vmlauncher | Run command using the Java VM's execution facilities where available. If set to false the underlying OS's shell, either directly or through the antRun scripts, will be used. Under some operating systems, this gives access to facilities not normally available through the VM 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 dir attribute, it may become necessary to set vmlauncher to false as well. | No, default is true |
| resolveexecutable | When this attribute is true, the name of the executable is resolved firstly against the project basedir 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 false. since Ant 1.6 | No, default is false |
| searchpath | When this attribute is true, then system path environment variables will be searched when resolving the location of the executable. since Ant 1.6.3 | No, default is false |
<exec dir="${src}" executable="cmd.exe" os="Windows 2000" output="dir.txt">
<arg line="/c dir"/>
</exec>
Command line arguments should be specified as nested
<arg> elements. See Command line arguments.
It is possible to specify environment variables to pass to the
system command via nested <env> elements.
| Attribute | Description | Required |
| key |
The name of the environment variable.
Note: (Since Ant 1.7) For windows, the name is case-insensitive. |
Yes |
| value | The literal value for the environment variable. | Exactly one of these. |
| path | The value for a PATH like environment variable. You can use ; or : as path separators and Ant will convert it to the platform's local conventions. | |
| file | The value for the environment variable. Will be replaced by the absolute filename of the file by Ant. |
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 all
Mapper 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.
<exec> is ignored; when you set
failonerror="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 code 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.
<exec executable="emacs"> <env key="DISPLAY" value=":1.0"/> </exec>
starts emacs on display 1 of the X Window System.
<property environment="env"/>
<exec ... >
<env key="PATH" path="${env.PATH}:${basedir}/bin"/>
</exec>
adds ${basedir}/bin to the PATH of the
system command.
<property name="browser" location="C:/Program Files/Internet Explorer/iexplore.exe"/>
<property name="file" location="ant/docs/manual/index.html"/>
<exec executable="${browser}" spawn="true">
<arg value="${file}"/>
</exec>
Starts the ${browser} with the specified ${file} and end the Ant process. The browser will remain.
<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.