## Uptodate

### Description

Sets a property if a target file or set of target files is more up-to-date than a source file or set of source files. A single source file is specified using the `srcfile` attribute. A set of source files is specified using the nested `<srcfiles>` elements. These are FileSets, whereas multiple target files are specified using a nested `<mapper>` element.

By default, the value of the property is set to `true` if the timestamp of the target file(s) is more recent than the timestamp of the corresponding source file(s). You can set the value to something other than the default by specifying the `value` attribute.

If a `<srcfiles>` element is used, without also specifying a `<mapper>` element, the default behavior is to use a merge mapper, with the `to` attribute set to the value of the `targetfile` attribute.

Normally, this task is used to set properties that are useful to avoid target execution depending on the relative age of the specified files.

### Parameters

Attribute | Description | Required
property | The name of the property to set. | Yes
value | The value to set the property to. | No; defaults to `true`.
srcfile | The file to check against the target file(s). | Yes, unless a nested `<srcfiles>` element is present.
targetfile | The file for which we want to determine the status. | Yes, unless a nested `<mapper>` element is present.

### Parameters specified as nested elements

#### srcfiles

The nested `<srcfiles>` element allows you to specify a set of files to check against the target file(s).

Note: You can specify either the `srcfile` attribute or nested `<srcfiles>` elements, but not both.

#### mapper

The nested `<mapper>` element allows you to specify a set of target files to check for being up-to-date with respect to a set of source files.

The mapper "to" attribute is relative to the target file, or to the "dir" attribute of the nested srcfiles element.

### Examples

      <uptodate property="xmlBuild.notRequired" targetfile="${deploy}\xmlClasses.jar" >
        <srcfiles dir= "${src}/xml" includes="**/*.dtd"/>
      </uptodate>

sets the property `xmlBuild.notRequired` to `true` if the `${deploy}/xmlClasses.jar` file is more up-to-date than any of the DTD files in the `${src}/xml` directory.

This can be written as:

      <uptodate property="xmlBuild.notRequired">
        <srcfiles dir= "${src}/xml" includes="**/*.dtd"/>
        <mapper type="merge" to="${deploy}\xmlClasses.jar"/>
      </uptodate>

as well. The `xmlBuild.notRequired` property can then be used in a `<target>` tag's `unless` attribute to conditionally run that target. For example, running the following target:

    <target name="xmlBuild" depends="chkXmlBuild" unless="xmlBuild.notRequired">
      ...
    </target>

will first run the `chkXmlBuild` target, which contains the `<uptodate>` task that determines whether `xmlBuild.notRequired` gets set. The property named in the `unless` attribute is then checked for being set/not set. If it did get set (ie., the jar file is up-to-date), then the `xmlBuild` target won't be run.

The following example shows a single source file being checked against a single target file:

      <uptodate property="isUpToDate"
                srcfile="/usr/local/bin/testit"
                targetfile="${build}/.flagfile"/>

sets the property `isUpToDate` to `true` if `/usr/local/bin/testit` is newer than `${build}/.flagfile`.

The following shows usage of a relative mapper.

        <uptodate property="checkUptodate.uptodate">
          <srcfiles dir="src" includes="*" />
          <mapper type="merge" to="../dest/output.done"/>
        </uptodate>
        <echo message="checkUptodate result: ${checkUptodate.uptodate}" />

The previous example can be a bit confusing, so it may be better to use absolute paths:

        <property name="dest.dir" location="dest"/>
        <uptodate property="checkUptodate.uptodate">
          <srcfiles dir="src" includes="*" />
          <mapper type="merge" to="${dest.dir}/output.done"/>
        </uptodate>

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