Section 7.3. Performing Batch Execution


7.3. Performing Batch Execution

What if you want to execute a command on multiple files? If you want to pass a set of files to an external command, use the apply task, a version of exec that takes filesets. The files in the fileset are passed as arguments to the command or external program.

This task is a powerful one, letting you batch your executions and work with external programs as if they supported filesets. In Example 7-5, the build file is running the C compiler gcc on a fileset. In this case, the apply task executes the command line gcc -c -o target source for each .c file in ${src}, where source with the name of each matching .c file in turn, and target is replaced with the name of the corresponding .o output file you want created.

Example 7-5. Using the apply task (ch07/apply/build.xml)
<?xml version="1.0" ?> <project default="main">     <property name="src" location="source" />     <target name="main">         <apply executable="gcc">             <arg value="-c"/>             <arg value="-o"/>             <targetfile/>             <srcfile/>             <fileset dir="${src}" includes="*.c" />             <mapper from="*.c" to="*.o" type="glob" />         </apply>     </target> </project>

You can see this task's attributes Table 7-4.

Table 7-4. The apply task's attributes

Attribute

Description

Required

Default

addsourcefile

Specifies if you want source filenames to be added to the command automatically. Since Ant 1.6.

No

TRue

append

Specifies whether you want to append to output and error files.

No

false

dest

Specifies the directory in which files will be stored by the task.

Yes, if you specify a nested mapper.

 

dir

Specifies the directory where the command should be executed.

No

 

error

Specifies the file where standard error output should be stored.

No

 

errorproperty

Specifies the name of a property where you want to store errors.

No

 

executable

Specifies the command to execute (without any command-line arguments).

Yes

 

failifexecutionfails

Specifies the build should be stopped if the program doesn't start.

No

true

failonerror

Specifies the build should be stopped if the task encounters errors.

No

 

forwardslash

Specifies you want filenames to be passed with forward slashes as directory separators.

No

false

input

Specifies the file where the task should take input to run the class with.

No

 

inputstring

Specifies a string holding the input stream for the class to run.

No

 

logError

Specifies you want to send error output to Ant's log.

No

 

maxparallel

Specifies the maximum number of source files to use at once. Set to a value less than or equal to 0 for unlimited parallelism. Available since Ant 1.6.

No

unlimited

newenvironment

Indicates you do not want to pass to the old environment when new environment variables are specified.

No

false

os

Specifies the operating systems in which the executable can be run.

No

 

output

Specifies the name of a file in which to store the output.

No

 

outputproperty

Specifies the name of a property in which you want the output of the task to be placed.

No

 

parallel

Specifies you want to run the command one time only on multiple files.

No

false

relative

Specifies if filenames should be absolute or relative when passed to the command to execute.

No

false

resolveExecutable

Specifies the name of the executable should be resolved using the project's base directory, then using the execution directory if that doesn't work. Since Ant 1.6.

No

false

resultproperty

Specifies the name of the property that you want to hold the return code. Use this one only if failonerror is false and if fork is true.

No

 

skipemptyfilesets

Specifies you don't want to run the command if no source files found or are newer than their corresponding target files.

No

false

spawn

Specifies you want to spawn a new process in which to run the command. To use this attribute, set fork to true.

No

false

timeout

Specifies you want the task to quit if it doesn't finish in the given time. Set the time in milliseconds.

No

 

type

Specifies whether you're working with files or directories. Set to dir, file, or both.

No

"file"

verbose

Specifies whether you want the task to display its progress. Since Ant 1.6.

No

false

Vmlauncher

Specifies you want to run the executable using the JVM's execution facilities.

No

true


You can use any number of nested fileset elements to specify the files you want to use with this task. Since Ant 1.6, you can use any number of nested filelist and/or dirset elements as well. At least one fileset or filelist is required.

You can use one mapper element to specify the target files relative to the dest attribute for dependency checking, as I'll do below. Command-line arguments can be passed with arg elements, as with the exec task, and you can use nested env elements.

How does Ant pass the names of files to the external program? By default, the file-names of the source files are added to the end of the command line. If you want to insert the names of files in a different place, use a nested srcfile element between nested arg elements. Nested targetfile elements are similar to srcfile elements, except they mark the position of the target filename on the command line. You can only use a targetfile element if you define a nested mapper and the dest attribute.



    Ant. The Definitive Guide
    Ant: The Definitive Guide, 2nd Edition
    ISBN: 0596006098
    EAN: 2147483647
    Year: 2003
    Pages: 115
    Authors: Steve Holzner

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