xml ed -u '/task-arguments/argument[@name="protocol"]/@default-value' -v 'string("tcp")' /tmp/test_xml/monitor.xml
xml ed -u '/task-arguments/argument[@name="port"]/@default-value' -v 'string("7223")' /tmp/test_xml/monitor.xml
xml ed -u '/task-arguments/argument[@name="username"]/@default-value' -v 'string("test")' /tmp/test_xml/monitor.xml

./sed.sh: line 4: 23932 Segmentation fault      xml ed -u '/task-arguments/argument[@name="protocol"]/@default-value' -v 'string("tcp")' /tmp/test_xml/monitor.xml
./sed.sh: line 5: 23933 Segmentation fault      xml ed -u '/task-arguments/argument[@name="port"]/@default-value' -v 'string("7223")' /tmp/test_xml/monitor.xml
./sed.sh: line 6: 23934 Segmentation fault      xml ed -u '/task-arguments/argument[@name="username"]/@default-value' -v 'string("test")' /tmp/test_xml/monitor.xml

#!/bin/sh

xmlfile_in="data.xml"
xmlfile_out="data.new"

protocol="tcp"
port="7223"
user="test"

sed -f /dev/stdin "$xmlfile_in" >"$xmlfile_out" <<END_SED
/argument name="protocol"/{
    i\\
<argument name="protocol" is-required="true" default-value="$protocol"/>
    d
}

/argument name="port"/{
    i\\
<argument name="port" is-required="true" default-value="$port"/>
    d
}

/argument name="username"/{
    i\\
<argument name="username" is-required="true" default-value="$user"/>
    d
}
END_SED