You could try xmllint

The xmllint program parses one or more XML files, specified on the command line as xmlfile. It prints various types of output, depending upon the options selected. It is useful for detecting errors both in XML code and in the XML parser itse

It allows you select elements in the XML doc by xpath, using the --pattern option.

On Mac OS X (Yosemite), it is installed by default.
On Ubuntu, if it is not already installed, you can run apt-get install libxml2-utils

Using bash and xmllint (as given by the tags):

xmllint --version  #  xmllint: using libxml version 20703

# Note: Newer versions of libxml / xmllint have a --xpath option which 
# makes it possible to use xpath expressions directly as arguments. 
# --xpath also enables precise output in contrast to the --shell & sed approaches below.
#xmllint --help 2>&1 | grep -i 'xpath'

{
# the given XML is in file.xml
host="$(echo "cat /config/global/resources/default_setup/connection/host/text()" | xmllint --nocdata --shell file.xml | sed '1d;$d')"
username="$(echo "cat /config/global/resources/default_setup/connection/username/text()" | xmllint --nocdata --shell file.xml | sed '1d;$d')"
password="$(echo "cat /config/global/resources/default_setup/connection/password/text()" | xmllint --nocdata --shell file.xml | sed '1d;$d')"
dbname="$(echo "cat /config/global/resources/default_setup/connection/dbname/text()" | xmllint --nocdata --shell file.xml | sed '1d;$d')"
printf '%s\n' "host: $host" "username: $username" "password: $password" "dbname: $dbname"
}

# output
# host: localhost
# username: root
# password: pass123
# dbname: testdb

In case there is just an XML string and the use of a temporary file is to be avoided, file descriptors are the way to go with xmllint (which is given /dev/fd/3 as a file argument here):

set +H
{
xmlstr='<?xml version="1.0"?>
<config>
    <global>
        <install>
            <date><![CDATA[Tue, 11 Dec 2012 12:31:25 +0000]]></date>
        </install>
        <crypt>
            <key><![CDATA[70e75d7969b900b696785f2f81ecb430]]></key>
        </crypt>
        <disable_local_modules>false</disable_local_modules>
        <resources>
            <db>
                <table_prefix><![CDATA[]]></table_prefix>
            </db>
            <default_setup>
                <connection>
                    <host><![CDATA[localhost]]></host>
                    <username><![CDATA[root]]></username>
                    <password><![CDATA[pass123]]></password>
                    <dbname><![CDATA[testdb]]></dbname>
                    <initStatements><![CDATA[SET NAMES utf8]]></initStatements>
                    <model><![CDATA[mysql4]]></model>
                    <type><![CDATA[pdo_mysql]]></type>
                    <pdoType><![CDATA[]]></pdoType>
                    <active>1</active>
                </connection>
            </default_setup>
        </resources>
        <session_save><![CDATA[files]]></session_save>
    </global>
    <admin>
        <routers>
            <adminhtml>
                <args>
                    <frontName><![CDATA[admin]]></frontName>
                </args>
            </adminhtml>
        </routers>
    </admin>
</config>
'

# exec issue
#exec 3<&- 3<<<"$xmlstr"
#exec 3<&- 3< <(printf '%s' "$xmlstr")
exec 3<&- 3<<EOF
$(printf '%s' "$xmlstr")
EOF

{ read -r host; read -r username; read -r password; read -r dbname; } < <(
       echo "cat /config/global/resources/default_setup/connection/*[self::host or self::username or self::password or self::dbname]/text()" | 
          xmllint --nocdata --shell /dev/fd/3 | 
          sed -e '1d;/d'
       )

printf '%s\n' "host: $host" "username: $username" "password: $password" "dbname: $dbname"

exec 3<&-
}
set -H


# output
# host: localhost
# username: root
# password: pass123
# dbname: testdb

Peter's answer is correct, but it outputs a trailing line feed.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output method="text"/>
  <xsl:template match="root">
    <xsl:for-each select="myel">
      <xsl:value-of select="@name"/>
      <xsl:text>,</xsl:text>
      <xsl:if test="not(position() = last())">
        <xsl:text>&#xA;</xsl:text>
      </xsl:if>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

Just run e.g.

xsltproc stylesheet.xsl source.xml

to generate the CSV results into standard output.

The following linux command uses XPath to access specified values within the XML file

for xml in `find . -name "*.xml"`
do  
echo $xml `xmllint --xpath "/param-value/value/text()" $xml`| awk 'NF>1'
done

Example output for matching XML files:

./test1.xml asdf
./test4.xml 1234