The following example which check if a string property contains a another string.

<project name="ant-string-contains-example" default="run" basedir=".">
  <target name="run">
    <property name="greeting" value="Hello World!"/>
    <condition property="hasWorld">
      <matches pattern="World" string="${greeting}"/>
    </condition>
    <fail message="No world in the greeting!" unless="hasWorld"/>
    <!-- Move on if no failture -->
    <echo message="Passed!"/>
  </target>
</project>

Done =)

Reference: StackOverflow – Ant: how to fail if property contains a certain string