xml - 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

Answer 1

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