I don't understand why you don't like split, but maybe a regex will be more to your liking?

use strict;
my $lineshapesline1 = 'SHAPES GREEN1;SIZE 240 500 340 930;SIZE 350 500
+ 240 590;SIZE 295 390 015 490;SIZE 350 210 760 300;SHAPES GREEN2;SIZE
+ 450 310 680 690;SIZE 450 110 680 490;SIZE 215 800 560 900;';
my @array;
while ( $lineshapesline1 =~ /(SHAPES.*?)(?=SHAPES|$)/g ) {
  push @array, $1;
}
print "$_\n" for @array;
__END__

SHAPES GREEN1;SIZE 240 500 340 930;SIZE 350 500 240 590;SIZE 295 390 0
+15 490;SIZE 350 210 760 300;
SHAPES GREEN2;SIZE 450 310 680 690;SIZE 450 110 680 490;SIZE 215 800 5
+60 900;
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