sed - How can I can insert the contents of a file into another file right before a specific line

Question

How can I can insert the contents of a file into another file right before a specific line using sed?

example I have file1.xml that has the following:

        <field tagRef="376">
        </field>
        <field tagRef="377">
        </field>
        <field tagRef="58">
        </field>
        <group ref="StandardMessageTrailer" required="true"/>
    </fieldList>
</message>

and file2.xml has the following:

        <field tagRef="9647">
            <description>Offset</description>
        </field>
        <field tagRef="9648">
            <description>Offset Units/Direction</description>
        </field>
        <field tagRef="9646">
            <description>Anchor Price</description>
        </field>

how can I insert the contents of file2 into file1 just before

<group ref="StandardMessageTrailer" required="true"/>

so it will look like this:

       <field tagRef="376">
        </field>
        <field tagRef="377">
        </field>
        <field tagRef="58">
        </field>
        <field tagRef="9647">
            <description>Offset</description>
        </field>
        <field tagRef="9648">
            <description>Offset Units/Direction</description>
        </field>
        <field tagRef="9646">
            <description>Anchor Price</description>
        </field>
        <group ref="StandardMessageTrailer" required="true"/>
    </fieldList>
</message>

I know how to insert after that line using

sed 'group ref="StandardMessageTrailer"/r file2.xml' file1.xml > newfile.xml  

but I want to insert it before.

appreciate the help

Answer 1

f2="$(<file2)"
awk -vf2="$f2" '/StandardMessageTrailer/{print f2;print;next}1' file1 

if you want sed, here's one way

sed  -e '/StandardMessageTrailer/r file2' -e 'x;$G' file1