Using your updated data which is now an array:-

knoppix@Microknoppix:~$ perl -Mstrict -wE '
> my @array = (
>    q{GAP_SPAN09 - GAP SPAN base (Scratch Testing [TSMC11] : tsmc11_w
+ld(sxfatd12j))},
>    q{GAP_SPAN03 - GAP SPAN base (DFD E2E Testing [TSPAN04] : tspan04
+-dfdint-wld(sxfamd6f))},
>    q{OS_WLI02 - POS_WLI02 Web Logic Integrator},
>    );
> my @newArray = 
>    map m{^(.*?)\s-\s},
>    @array;
> say for @newArray;'
GAP_SPAN09
GAP_SPAN03
OS_WLI02
knoppix@Microknoppix:~$
[download]

I hope this is helpful.