php - Regex to allow all characters except repeats of a particular given character -

i've been fumbling bit , thought i'd put regex experts:

i want match strings this:

abc[abcde]fff abcffasd 

so want allow single brackets (e.g. [ or ]). however, don't want allow double brackets in sequence (e.g. [[ or ]]).

this means string shouldn't pass regex:

abc[abcde]fff[[gg]] 

my best guess far based on an example found, like:

(?>[a-za-z\[\]']+)(?!\[\[) 

however, doesn't work (it matches when double brackets present), presumably because brackets contained in first part well.

you want like:

^(?:\[?[^\[]|\[$)*$ 

at each character, pattern accepts opening bracket followed character, or end of string.

or little more neatly, using negative lookahead:

^(?:(?!\[\[).)*$ 

here, pattern match characters long doesn't see 2 [[ ahead.