#increment and check counter (if the variable doesn't exist it is basically zero, becoming 1 after the increment)
inc=$counter
if=($counter > 5) set=$counter:1
 
if=($counter = 1) do=count1
if=($counter = 2) do=count2
if=($counter = 3) do=count3
if=($counter = 4) do=count4
if=($counter = 5) do=count5
exit
 
:count1
echo="First call!" 
exit
 
:count2
echo="Second call!" 
exit
 
:count3
echo="Third call!" 
exit
 
:count4
echo="Fourth call!" 
exit
 
:count5
echo="Fifth call - starting over!" 
exit

A more simplified version would look like this – if you just need the actual number:

#increment and check counter (if the variable doesn't exist it is basically zero, becoming 1 after the increment)
inc=$counter
if=($counter > 5) set=$counter:1
 
echo="This is call number {$counter} of 5!" 

Note: Global variables are shared across all alerts so make sure to either chose unique names or add preprocessor placeholders like [id] or [name] to the variable name, eg. inc=$count[id]!