How to pull out a substring in Ant

问题:

Is there a way to pull a substring from an Ant property and place that substring into it's own property?

回答1:

I use scriptdef to create a javascript tag to substring, for exemple:

 <project>
  <scriptdef name="substring" language="javascript">
     <attribute name="text" />
     <attribute name="start" />
     <attribute name="end" />
     <attribute name="property" />
     <![CDATA[
       var text = attributes.get("text");
       var start = attributes.get("start");
       var end = attributes.get("end") || text.length();
       project.setProperty(attributes.get("property"), text.substring(start, end));
     ]]>
  </scriptdef>
  ........
  <target ...>
     <substring text="asdfasdfasdf" start="2" end="10" property="subtext" />
     <echo message="subtext = ${subtext}" />
  </target>
 </project>

回答2:

You could try using PropertyRegex from Ant-Contrib.

   <propertyregex property="destinationProperty"
              input="${sourceProperty}"
              regexp="regexToMatchSubstring"
              select="\1"
              casesensitive="false" />

回答3:

Since I prefer to use vanilla Ant, I use a temporary file. Works everywhere and you can leverage replaceregex to get rid of the part of the string you don't want. Example for munging Git messages:

    <exec executable="git" output="${git.describe.file}" errorproperty="git.error" failonerror="true">
        <arg value="describe"/>
        <arg value="--tags" />
        <arg value="--abbrev=0" />
    </exec>
    <loadfile srcfile="${git.describe.file}" property="git.workspace.specification.version">
        <filterchain>
           <headfilter lines="1" skip="0"/>
           <tokenfilter>
              <replaceregex pattern="\.[0-9]+$" replace="" flags="gi"/>
           </tokenfilter>
           <striplinebreaks/>
        </filterchain>
    </loadfile>

回答4:

I would go with the brute force and write a custom Ant task:

public class SubstringTask extends Task {

    public void execute() throws BuildException {
        String input = getProject().getProperty("oldproperty");
        String output = process(input);
        getProject().setProperty("newproperty", output);
    }
}

What's left it to implement the String process(String) and add a couple of setters (e.g. for the oldproperty and newproperty values)

回答5:

i would use script task for that purpose, i prefer ruby, example cut off the first 3 chars =

<project>
  <property name="mystring" value="foobarfoobaz"/>  
   <target name="main"> 
    <script language="ruby">
     $project.setProperty 'mystring', $mystring[3..-1]
    </script>
    <echo>$${mystring} == ${mystring}</echo>
   </target>    
  </project>

output =

main:
     [echo] ${mystring} == barfoobaz

using the ant api with method project.setProperty() on an existing property will overwrite it, that way you can work around standard ant behaviour, means properties once set are immutable