Returns true if the event matches the search string X.

 Find below the skeleton of the usage of the function “searchmatch” with EVAL : 
                 | eval AA=if(searchmatch(“Queue Full”),”Exists”,”NOT”) 
Explanation :
         If any event in the “_internal” index is
         having Queue Full” String in it, then
         “Exists” will be stored in the “AA” field
         which is newly created.If not then “NOT
         will be stored in the “AA” So, there are
         total 5990 lines with “Queue Full” and
         5452 without “Queue Full
Verification :
             | eval AA=if(searchmatch(“Queue Full”),
             | search AA=”Exists”
Only those lines will appear which has “Exists
value in AA field, which means “Queue Full” string
is there in the event.
Similarly , you can also verify for AA=”NOT” and you
will get only those lines which do not contain
“Queue Full” String in it.
Now you can effectively utilize “searchmatch” 
function with “eval” command to meet your requirement !!

Hope you are now comfortable in

Usage of Splunk EVAL Function : SEARCHMATCH