答案

1. /xml/block/el[not(@name)]
2. 如其他答案所述:

您不能直接插入带有属性的元素，但因为每个编辑操作都是按顺序执行的，您可以插入一个元素，然后添加一个属性.

命令

xmlstarlet ed -a '/xml/block/el[@name="b"]' \-t 'elem' -n 'el' -v 0 \-i '/xml/block/el[not(@name)]' \-t '属性' -n '名称' -v 'c'

Source XML

<xml>
    <block>
        <el name="a">92346</el>
        <el name="b">lorem</el>
    </block>
    <block>
        <el name="a">89753</el>
        <el name="b">ipsum</el>
    </block>
</xml>

Object

I would like to insert an <el name="c">0</el> element in every <block> with a Linux shell script:

<xml>
    <block>
        <el name="a">92346</el>
        <el name="b">lorem</el>
        <el name="c">0</el>
    </block>
    <block>
        <el name="a">89753</el>
        <el name="b">ipsum</el>
        <el name="c">0</el>
    </block>
</xml>

I can append the elements using XmlStarlet:

xmlstarlet ed -a '/xml/block/el[@name="b"]' \
              --type 'elem' -n 'el' -v 0

Questions

1. What is the XPath expression that selects every <el> element which doesn't have a name attribute?
2. Can I append the elements and insert the attributes with a single xml ed command?

Answers

1. /xml/block/el[not(@name)]
2. As stated in an other answer:

You can't insert an element with an attribute directly but since every edit operation is performed in sequence, you can insert an element and then add an attribute.

The command

xmlstarlet ed -a '/xml/block/el[@name="b"]' \
              -t 'elem' -n 'el' -v 0 \
              -i '/xml/block/el[not(@name)]' \
              -t 'attr' -n 'name' -v 'c'