How to refine my data using substring-findstring

Hi Gurus,

I have a col that has data like this.

test-name[00H]
test2-something[00H] 

I only want to get

test-name

test2-something

Right now, I have SUBSTRING(col1,FINDSTRING(col1,"[",1) + 1,FINDSTRING(col1,"]",1) - 5)m but I am getting error saying

"[Derived Column [34374]] Error: An error occurred while evaluating the function."

Please help me with this.