having a little trouble with this rather basic script. This script works on Bash in my macbook pro, but not on my Linux Mint desktop, which also uses bash.

I can't figure out what;s wrong with it, unless I'm making a rookie error or assumption.

Any help would be appreciated, thanks.

EDIT***
Here is the updated code, and I'm still getting an error from bash saying:

line 6: [: -lt: unary operator expected
line 16: [: -gt: unary operator expected


    #!/bin/bash
    clear
    counter=0
    
    function countup {
    while [ $counter -lt 500 ]
    do
      ((counter++))
      echo $counter
      sleep 0.2
    done
    countdown
    }
    
    function countdown {
    while [ $counter -gt 0 ]
    do
      ((counter--))
      echo $counter
      sleep 0.2
    done
    countup
    }
    
    countup