Unable to scan only modified files with php lint

im trying to run an ant build which executes some php linting function only over modified files. this used to work using jenkins, but lost this possibility when using circleci.

<target name="lint">
    <apply executable="php" failonerror="true">
        <arg value="-l"/>
        <fileset dir="${basedir}">
            <include name="system/application/**/*.php"/>
            <modified />

is there any way to run this command only on files modified in the current build? what might be happening? which is the circleci way of doing this?