Replaceregexp with property value depending on the matched group - ant

Question

I'd like to replace some replace marks in css files with values out of a property file. What i did so far is:
<target depends="prepare" name="build_css">
<replaceregexp>
<fileset refid="temp_css_files"/>
<regexp pattern="\{(.*)\}"/>
<substitution expression="${testprop}"/>
</replaceregexp>
</target>
which will successfully replace the matched string with the value of the testprop property.But what i like to do is, to replace the matched string by a property whose name is the matched string.
So a replacement mark {myprop} will be replaced by the value of the property myprop.
I tried:
<target depends="prepare" name="build_css">
<replaceregexp>
<fileset refid="temp_css_files"/>
<regexp pattern="\{(.*)\}"/>
<substitution expression="${\1}"/>
</replaceregexp>
</target>
with no success since the matched string is then replaced by the String ${myprop}.
Is it possible to to this? Or is there an easier way with another task that i'm missing?

Answer 1

If you can use the typical Ant ${...} syntax to represent properties in your CSS files, then Ant's <expandproperties> FilterReader may be useful:
<project name="ant-replace-tokens-with-copy-task" default="run">
<target name="run">
<property name="src-root" location="src"/>
<fileset id="temp_css_files" dir="${src-root}">
<include name="**/*.css"/>
</fileset>
<!-- The <copy> task cannot "self-copy" files. So, for each -->
<!-- matched file we'll have <copy> read the file, replace the -->
<!-- tokens, and write the result to a temporary file. Then, we'll -->
<!-- use the <move> task to replace the original files with the -->
<!-- modified files. -->
<property name="filtered-file.extension" value="*.filtered-file"/>
<copy todir="${src-root}">
<fileset refid="temp_css_files"/>
<globmapper from="*" to="${filtered-file.extension}"/>
<filterchain>
<expandproperties/>
</filterchain>
</copy>
<move todir="${src-root}">
<fileset dir="${src-root}" includes="**"/>
<globmapper from="${filtered-file.extension}" to="*"/>
</move>
</target>
</project>
If you need to stick with the {...} syntax, the ReplaceTokens FilterReader replaces tokens with properties defined in a properties file:
<project name="ant-replace-tokens-with-copy-task" default="run">
<target name="run">
<property name="src-root" location="src"/>
<fileset id="temp_css_files" dir="${src-root}">
<include name="**/*.css"/>
</fileset>
<!-- The <copy> task cannot "self-copy" files. So, for each -->
<!-- matched file we'll have <copy> read the file, replace the -->
<!-- tokens, and write the result to a temporary file. Then, we'll -->
<!-- use the <move> task to replace the original files with the -->
<!-- modified files. -->
<property name="filtered-file.extension" value="*.filtered-file"/>
<copy todir="${src-root}">
<fileset refid="temp_css_files"/>
<globmapper from="*" to="${filtered-file.extension}"/>
<filterchain>
<filterreader classname="org.apache.tools.ant.filters.ReplaceTokens">
<param type="tokenchar" name="begintoken" value="{"/>
<param type="tokenchar" name="endtoken" value="}"/>
<param type="propertiesfile" value="dev.properties"/>
</filterreader>
</filterchain>
</copy>
<move todir="${src-root}">
<fileset dir="${src-root}" includes="**"/>
<globmapper from="${filtered-file.extension}" to="*"/>
</move>
</target>
</project>