Thanks again!!. I tried as shown below.Only the last one is working correctly. Rest all other tokens are being evaluated to null.
<eval token="error_code">case(match($click.value$, "Connection is closed"), "ERRORCODE=-4470")</eval>
<eval token="error_code">case(match($click.value$, "Connection Refused"), "ERRORCODE=-4499")</eval>
<eval token="error_code">case(match($click.value$, "Connection Authorization Failure"), "ERRORCODE=-4214")</eval>
<eval token="error_code">case(match($click.value$, "Unknown Host"), "ERRORCODE=-4222")</eval>
<link target="_blank">search?q=index="xyz" attrs.io.kubernetes.pod.namespace=abx-int "$error_code$" earliest=$Intergration_Errors_Time_Range_Picker.earliest$&latest=$Intergration_Errors_Time_Range_Picker.latest$</link>
</drilldown>
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