Using XML::XSH2, a wrapper around XML::LibXML:

stream :f datafile_towns.xml :F /dev/null select town {
    if (location/mapx > 500) {
        echo :n :s (towndata/townname) , (player/playeralliance/allian
+ceticker) ;
        echo :n :s , (player/playername) , (towndata/townname) , (loca
+tion/mapy) ;
        echo :s , (location/mapx);
        rm . ;
    }
}
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On MSwin, replace /dev/null with NUL.