Question

I’m guessing it stands for less than based on the output, but where can I find documentation about this syntax?

     #!/bin/bash 
     COUNTER=0
     while [  $COUNTER -lt 10 ]; do
         echo The counter is $COUNTER
         let COUNTER=COUNTER+1 
     done

Answer 1

-lt is less than (strictly).

The man page you’re looking for is man test.

n1 -lt  n2  

True if the integer n1 is algebraically less than the integer n2; otherwise, false.

n1 -le  n2  

True if the integer n1 is algebraically less than or equal to the integer n2; otherwise, false.