@flzhang132 <init> section is available post Splunk Enterprise 6.5 which works only with Simple XML Dashboards, so documenting a workaround of using independent search with search event handler. (PS: prior to Splunk Enterprise 6.5 they were <preview> and <finalized> instead of <progress> and <done> from 6.5 onward).
<search>
<query>| makeresults
| eval prev_month=strftime(relative_time(now(),"-1mon@mon"),"%Y%m")
</query>
<done>
<set token="prev_month">$result.prev_month$</set>
</done>
</search>
Please refer to using <eval> to set token using relative_time() will use Client Time Zone: http://docs.splunk.com/Documentation/Splunk/latest/Viz/tokens#Define_token_filtering_and_formatting
1) With independent <search> you should be able to perform complicated searches to fetch result to set required token.
2) You should also add depends attribute with the default value token to the <input> to ensure that it is displayed only when the default value is set.
Following is a run anywhere example:
<form>
<label>Initialize form variables on load</label>
<search>
<query>| makeresults
| eval prev_month=strftime(relative_time(now(),"-1mon@mon"),"%Y%m")
</query>
<done>
<set token="prev_month">$result.prev_month$</set>
</done>
</search>
<fieldset submitButton="false">
<input type="dropdown" token="ymmon" depends="$prev_month$">
<label>Date</label>
<choice value="ym201801">201801</choice>
<choice value="ym201802">201802</choice>
<choice value="ym201803">201803</choice>
<choice value="ym201804">201804</choice>
<choice value="ym201805">201805</choice>
<choice value="ym201806">201806</choice>
<choice value="ym201807">201807</choice>
<choice value="ym201808">201808</choice>
<choice value="ym201809">201809</choice>
<choice value="ym201810">201810</choice>
<default>$prev_month$</default>
<initialValue>$prev_month$</initialValue>
</input>
</fieldset>
<row>
<panel>
<html>
<div>prev_month: $prev_month$</div>
</html>
</panel>
</row>
</form>
____________________________________________
| makeresults | eval message= "Happy Splunking!!!"
