## DependSet

A task to manage arbitrary dependencies between files.

### Description

The dependset task compares a set of source files with a set of target files. If any of the source files is more recent than any of the target files, all of the target files are removed.

Source files and target files are specified via nested FileSets and/or nested FileLists. Arbitrarily many source and target filesets/filelists may be specified, but at least one filelist/fileset is required for both sources and targets.

Use a FileSet when you want to use wildcard include or exclude patterns and don't care about missing files. Use a FileList when you want to consider the non-existence of a file as if it were out of date. If there are any non-existing files in any source or target FileList, all target files will be removed.

DependSet is useful to capture dependencies that are not or cannot be determined algorithmically. For example, the `<style>` task only compares the source XML file and XSLT stylesheet against the target file to determined whether to restyle the source. Using dependset you can extend this dependency checking to include a DTD or XSD file as well as other stylesheets imported by the main stylesheet.

### Parameters

(none)

### Parameters Specified as Nested Elements

#### srcfileset

The nested `srcfileset` element specifies a FileSet. All files included in this fileset will be compared against all files included in all of the `targetfileset` filesets and `targetfilelist` filelists. Multiple `srcfileset` filesets may be specified.

#### srcfilelist

The nested `srcfilelist` element specifies a FileList. All files included in this filelist will be compared against all files included in all of the `targetfileset` filesets and `targetfilelist` filelists. Multiple `srcfilelist` filelists may be specified.

#### targetfileset

The nested `targetfileset` element specifies a FileSet. All files included in this fileset will be compared against all files included in all of the `srcfileset` filesets and `sourcefilelist` filelists, and if any are older, they are all deleted. Multiple `targetfileset` filesets may be specified.

#### targetfilelist

The nested `targetfilelist` element specifies a FileList. All files included in this filelist will be compared against all files included in all of the `srcfileset` filesets and `sourcefilelist` filelists, and if any are older, they are all deleted. Multiple `targetfilelist` filelists may be specified.

### Examples

>         <dependset>
>            <srcfilelist
>                dir   = "${dtd.dir}"
>                files = "paper.dtd,common.dtd"/>
>            <srcfilelist
>                dir   = "${xsl.dir}"
>                files = "common.xsl"/>
>            <srcfilelist
>                dir   = "${basedir}"
>                files = "build.xml"/>
>            <targetfileset
>                dir      = "${output.dir}"
>                includes = "**/*.html"/>
>         </dependset>

In this example derived HTML files in the ${output.dir} directory will be removed if any are out-of-date with respect to:

1. the DTD of their source XML files
2. a common DTD (imported by the main DTD)
3. a subordinate XSLT stylesheet (imported by the main stylesheet), or
4. the buildfile

If any of the source files in the above example does not exist, all target files will also be removed. To ignore missing source files instead, use filesets instead of filelists for the source files.

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