How to add an attribute in a tag in XML file by command-line?

Question

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" 

Answer 1

You should not parse XML with sed; use an XML parser such as xmlstarlet instead. For your task it would be:

xmlstarlet ed -O --inplace --insert "/book" --type attr -n Book_Width -v A xml_file 

The file content is then:

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

• The ed means edit mode to edit the XML tree.
• -O omits the XML tag.
• We want to insert something with --insert.
• "/book" is the path where to insert.
• --type attr: it's an attribute we want to insert.
• The name -n of the attribute.
• The value -v.

Answer 2

in sed "a" appends a pattern IN A NEW LINE.

what you want to do is replace (substitute). Let's use a colon as separator for clarity:

sed 's:\(<book.*\)\(/>\):\1 Book_Width="A"\2:' 

anything in \( .. \) is a pattern memorized by the order of appearance and recalled by \indexnumber , e.g. \1 will reproduce the first pattern saved.

So we are memorizing <book name="Sed tutorial" price="250" as pattern 1 and /> as pattern 2 and just insert Book_Width="A" in the middle.

echo '<book name="Sed tutorial" price="250"/>' | sed 's:\(<book.*\)\(/>\):\1 Book_Width="A"\2:' <book name="Sed tutorial" price="250" Book_Width="A"/> 

Answer 3

Assuming that your XML file is literally just a single line with a book node, as shown in the question, you may add a Book_Width attribute to that book node using xq (part of yq from https://kislyuk.github.io/yq/) like so:

$ xq -x '.book."@Book_Width" |= "A"' file.xml <book name="Sed tutorial" price="250" Book_Width="A"></book> 

If you have data that you'd like to insert as the attribute's value:

$ myvariable='20 cm' $ xq -x --arg val "$myvariable" '.book."@Book_Width" |= $val' file.xml <book name="Sed tutorial" price="250" Book_Width="20 cm"></book> 

Answer 4

With awk you can do something like this:

Supposing the line is in file file1.xml then:

awk -F '/' '{print $1,"Book_Width=\"A\"",FS,$2}' file1.xml 

Answer 5

The solution would be to use sed and not use any external packages or commands.

echo '<book name="Sed tutorial" price="250"/>' | sed 's/<book /& Book_Width="A"/' 

Output:

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

If you have a file.

sed 's/<book /& Book_Width="A"/' ${FILE_NAME} 

or if you want to replace inplace

sed -i 's/<book /& Book_Width="A"/' ${FILE_NAME} 

&: This symbol is a special character in sed that represents the entire matched string, i.e., <book(space). We use it here in the replacement pattern to include the original <book tag in the modified text.