Remove referenced duplicate entries from XML file

Question

After hours beating my head against the wall, I decided this is [probably] not the job for a mere shell script.

There's a bug on Google Earth that makes loading KML files very slow: for almost every new Placemark you create, it creates 2 new Styles, references both Styles on a StyleMap in <styleUrl>, and then references the StyleMap on the Placemark:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<Document>
    <StyleMap id="m_ylw-pushpin">
        <Pair>
            <key>normal</key>
            <styleUrl>#s_ylw-pushpin</styleUrl>
        </Pair>
        <Pair>
            <key>highlight</key>
            <styleUrl>#s_ylw-pushpin_hl</styleUrl>
        </Pair>
    </StyleMap>
    <Style id="s_ylw-pushpin">
        <IconStyle>
            <scale>1.1</scale>
            <Icon>
                <href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
            </Icon>
            <hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
        </IconStyle>
    </Style>
    <Style id="s_ylw-pushpin_hl">
        <IconStyle>
            <scale>1.3</scale>
            <Icon>
                <href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
            </Icon>
            <hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
        </IconStyle>
    </Style>

    <StyleMap id="msn_ylw-pushpin">
        <Pair>
            <key>normal</key>
            <styleUrl>#sn_ylw-pushpin</styleUrl>
        </Pair>
        <Pair>
            <key>highlight</key>
            <styleUrl>#sh_ylw-pushpin</styleUrl>
        </Pair>
    </StyleMap>
    <Style id="sn_ylw-pushpin">
        <IconStyle>
            <scale>1.1</scale>
            <Icon>
                <href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
            </Icon>
            <hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
        </IconStyle>
    </Style>
    <Style id="sh_ylw-pushpin">
        <IconStyle>
            <scale>1.3</scale>
            <Icon>
                <href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
            </Icon>
            <hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
        </IconStyle>
    </Style>

    <Placemark>
        <LookAt>
            <altitude>0</altitude>
            <tilt>0</tilt>
            <gx:altitudeMode>relativeToSeaFloor</gx:altitudeMode>
        </LookAt>
        <styleUrl>#m_ylw-pushpin</styleUrl>
        <Point>
            <gx:drawOrder>1</gx:drawOrder>
        </Point>
    </Placemark>
    <Placemark>
        <LookAt>
            <altitude>1</altitude>
            <tilt>0</tilt>
            <gx:altitudeMode>relativeToSeaFloor</gx:altitudeMode>
        </LookAt>
        <styleUrl>#msn_ylw-pushpin</styleUrl>
        <Point>
            <gx:drawOrder>0</gx:drawOrder>
        </Point>
    </Placemark>
</Document>
</kml>

• sh_ylw-pushpin and s_ylw-pushpin_hl are duplicate entries with just a different name (id). Each is referenced on a different StyleMap. The same applies to sn_ylw-pushpin and s_ylw-pushpin.
• If we remove the duplicate Styles and fix their references (eg. s/\<sh_ylw-pushpin\>/s_ylw-pushpin_hl/), we will be left with duplicate StyleMaps too, so we should repeat the deduplication on them too.

Summarizing, what I need is to get rid of the duplicate entries from the XML file (leaving just one), and update all references of the removed entries to the one that was left.

Answer 1

Since you seem to know what you want to do I would suggest trying to do this using the command line tool xmlstartlet. It looks like you can delete entries from the KML/XML file programmatically.

References

• man page for xmlstarlet
• tutorial on using xmlstarlet
• IBM Developer Works Tutorial on xmlstartlet

NOTE: The IBM tutorial references the tool as xml, just swap that out with xmlstarlet.