use xmlstarlet in shell script to read script variable value and insert in outpu xml file under specific section if the string is not present there

[vivuu1989]

The parse yaml utility which I used in my shell script produces variables as below by eval command

policy1_name='ipfilter'
policy1_scope='api'
policy1_apiname='apiname'
policy1_inboundsession='rate-limit-by-key calls="25" renewal-period="60"
counter-key="@\(Regex.Match\(context.xxx.xxxx.GetValueOrDefault\("X-xxxxxxx-For",""\), @"^[.0-9]*"\)?.Value\)'
policy1_outboundsession_ipAddressesFrom='1xxxxxxxx'
policy1_outboundsession_ipAddressesTo='1yyyyyyy'
policy1_=' policy1_name policy1_scope policy1_apiname policy1_inboundsession policy1_outboundsession'
policy1_outboundsession_=' policy1_outboundsession_ipAddressesFrom policy1_outboundsession_ipAddressesTo'
policy_=' policy1'

I know, I can use xmlstarlet to create element inside my outputpolicy.xml file as given below.

for g in $(eval echo \$${f}_apiname); do
     echo " this policy will be applied to apis,$(eval echo \$${f}_apiname)"
    done
      if [ -z "$(eval echo \$${f}_inboundsession_)" ]; then
        echo 'the inbound session is not present'
      else
        echo 'the inbound session is present and append the policy settings to inbound'
        xmlstarlet ed -O  -s '//inbound' -t elem -n rate-limit-by-key  -i '//inbound/rate-limit-by-key' -t attr -n calls -v xx -i '//inbound/rate-limit-by-key' -t attr -n renewal-period -v yy -i '//inbound/rate-limit-by-key' -t attr -n counter-key -v '@(Regex.Match(context.x.y.GetValueOrDefault("xxxxxxx",""), @"^[.x-y]*")?.Value)' policy.xml > io_ou_ipfilter.xml

but what I am looking is use xmlstarlet in my script to read the output of the above script variable "$(eval echo $${f}inboundsession) and insert the given string under inbound session of the below policy.xml file if the string is not preset.

Expected Output

<policies>
    <inbound>
	  <base />
      <rate-limit-by-key calls="xxx" renewal-period="xx" counter-key="@(Regex.Match(context.x.y.GetValueOrDefault("xxxxxxx",""), @"^[.x-y]*")?.Value)" />
    </inbound>
    <backend>
	  <base />
    </backend>
    <outbound>
	  <base />
    </outbound>
    <on-error>
	  <base />
    </on-error>
</policies>