How to insert a new element under another with xmlstarlet?

Question

$ vim test.xml

<?xml version="1.0" encoding="UTF-8" ?>
<config>
</config>
$ xmlstarlet ed -i "/config" -t elem -n "sub" -v "" test.xml
<?xml version="1.0" encoding="UTF-8"?>
<sub></sub>
<config>
</config>

But I wanted sub to be a child of config. How should I change the xpath parameter of -i?

BONUS: Is it possible to insert the child directly with an attribute and even have it set to a value? Something like:

$ xmlstarlet ed -i "/config" -t elem -n "sub" -v ""  -a attr -n "class" -v "com.foo" test.xml

Solution 1

Use -s (or --subnode) instead of -i. Regarding the bonus, you can't insert an element with an attribute directly but since every edit operation is performed in sequence, to insert an element and then add an attribute:

> xml ed -s /config -t elem -n sub -v "" -i /config/sub -t attr -n class -v com.foo test.xml
<?xml version="1.0" encoding="UTF-8"?>
<config>
<sub class="com.foo"></sub></config>

Solution 2

I had a similar problem: I had a Tomcat configuration file (server.xml), and had to insert a <Resource> tag with pre-defined attributes into the <GlobalNamingResources> section.

Here is how it looked before:

<GlobalNamingResources>
    <!-- Editable user database that can also be used
         by UserDatabaseRealm to authenticate users
    -->
    <Resource name="UserDatabase"
              auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
</GlobalNamingResources>

Here is what I wanted to achieve:

<GlobalNamingResources>
    <!-- Editable user database that can also be used
         by UserDatabaseRealm to authenticate users
    -->
    <Resource name="UserDatabase"
              auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
    <Resource name="jdbc/templateassets"
              auth="Container"
              type="javax.sql.DataSource"
              driverClassName="com.mysql.jdbc.Driver"
              url="jdbc:mysql://DBHOST:DBPORT/DBNAME?createDatabaseIfNotExist=false&amp;useUnicode=true&amp;characterEncoding=utf-8"
              username="DBUSER"
              password="DBPASS"
              maxActive="150"
              maxIdle="10"
              initialSize="10"
              validationQuery="SELECT 1"
              testOnBorrow="true" />
</GlobalNamingResources>

Here is how I did it (snippet from a shell script):

if [ -n "$(xmlstarlet sel -T -t -v "/Server/GlobalNamingResources/Resource[@name='jdbc/templateassets']/@name" server.xml)" ]; then
  echo "Resource jdbc/templateassets already defined in server.xml"
else
  echo "Adding resource jdbc/templateassets to <GlobalNamingResources> in server.xml"
  xmlstarlet ed -P -S -L -s /Server/GlobalNamingResources -t elem -n ResourceTMP -v "" \
    -i //ResourceTMP -t attr -n "name" -v "jdbc/templateassets" \
    -i //ResourceTMP -t attr -n "auth" -v "Container" \
    -i //ResourceTMP -t attr -n "type" -v "javax.sql.DataSource" \
    -i //ResourceTMP -t attr -n "driverClassName" -v "com.mysql.jdbc.Driver" \
    -i //ResourceTMP -t attr -n "url" -v "jdbc:mysql://DBHOST:DBPORT/DBNAME?createDatabaseIfNotExist=false&useUnicode=true&characterEncoding=utf-8" \
    -i //ResourceTMP -t attr -n "username" -v "DBUSER" \
    -i //ResourceTMP -t attr -n "password" -v "DBPASS" \
    -i //ResourceTMP -t attr -n "maxActive" -v "150" \
    -i //ResourceTMP -t attr -n "maxIdle" -v "10" \
    -i //ResourceTMP -t attr -n "initialSize" -v "10" \
    -i //ResourceTMP -t attr -n "validationQuery" -v "SELECT 1" \
    -i //ResourceTMP -t attr -n "testOnBorrow" -v "true" \
    -r //ResourceTMP -v Resource \
    server.xml
fi

The trick is to temporarily give a unique name to the new element, so that it can be found later with an XPATH expression. After all attributes have been added, the name is changed back to Resource (with -r).

The meaning of the other xmlstarlet options:

-P (or --pf)        - preserve original formatting
-S (or --ps)        - preserve non-significant spaces
-L (or --inplace)   - edit file inplace

Solution 3

From version 1.4.0 of XMLStarlet (dated 2012-08-26), you can use $prev (or $xstar:prev) as the argument to -i, -a, and -s to refer to the last nodeset inserted. See the examples in the XMLStarlet source code in the files doc/xmlstarlet.txt, examples/ed-backref1, examples/ed-backref2, and examples/ed-backref-delete. You no longer need to use the trick of inserting the element with a temporary element name and then renaming it at the end. The example examples/ed-backref2 is particularly helpful in showing how to define a variable to use to refer to a (the) previously-created note so that you don't need to do tricks such as $prev/.. to "navigate" out of a node.

Solution 4

As mentioned by @npoostavs the correct answer is to use 'subnode'. To improve the answer with the new '$prev' you can do the following:

xml ed --inplace \
       --subnode /config --type elem --name "sub" \
       --var new_node '$prev' \
       --insert '$new_node' --type attr --name "class" --value "com.foo" \ 
       test.xml

With the following explanation:

--inplace    Change the file "test.xml" directly
--subnode    Add a new node called "class" below "/config"
--var        Assign the newly created node to the variable new_node 
             Use single quotes to prevent bash replacing the variable
--insert     Insert attribute and value to the newly created node

Solution 5

The example did not work until I wrapped <GlobalNamingResources> into a <Server> element.

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Comments

[Bernhard Hofmann]

That last edit action (rename) is a game changer. Thank you so much for that!

[marsbard]

+1 on the rename, nice way to make sure you are getting just your resource for editing and then rename at the end, thanks.

[Warren Rox]

The problem with this approach is that any other XML elements with the same name acquire the attribute as well which is likely undesired. A way around this is to add the element with a temporary name that you can XPath to uniquely and add the attribute and subsequently remain the element when you're done.

[Frederick Nord]

cool, can you cook up a nicer version of the answer with the (currently) highest votes? stackoverflow.com/a/9172796/2015768