I am trying to add field at the end of tag using sed script. Suppose I have a tag in XML file:

```
<book name="Sed tutorial" price="250"/>

```

Now I want to add field as `Book_Width="A"` after end of `<book/>` tag so that my tag becomes:

```
<book name="Sed tutorial" price="250" Book_Width="A"/>

```

I tried with `sed`:

```
sed '/<book "[^>]*>/ a Book_Width="A"'

```

but it gives:

```
<book name="Sed tutorial" price="250"/>
Book_Width="A"

```