regex - Ruby Regexp trouble. How to accept a string only if it doesnt have 'foo' -

i need regex accept this:

"add chain=input comment="test" protocol=icmp blah blah other stuff" 

but not accept this:

"add chain=input comment="test" blah blah disabled=yes 

so if @ end of string says disabled=yes, don't match it. i've tried this:

(add action=drop chain=input .*(?!disabled=yes)) add action=drop chain=input [^disabled=yes] add action=drop chain=input.*[^(disabled=yes)] 

and couple other variations no avail. doing incorrectly?

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edit:

def check( line, key )   return line[ key ] ? true : false end  check( "add action=drop chain=input comment="test" disabled=yes", /add action=drop chain=input.*[^(disabled=yes)]/ ) 

this of code, broken down.

use negative lookahead based regex below.

^(?!.*disabled=yes$)add(?: action=drop)? chain=input.* 

rubular

(?!.*disabled=yes$) negative lookahead asserts there isn't string disabled=yes present @ last. , did make action=drop string optional because didn't find on input string on regex.