my $str = "ABC[GHI]XYZ";

# Note that in actual situation string may contain several
# such bracketed alphabets.

##</code><code>##

my @array = ("A", "B", "C", "GHI", "X", "Y", "Z");

##</code><code>##

perl -MData::Dumper -e '
$str ="ABC[GHI]XYZ"; 
@arr= split(/[\[\]]/,$str); 
print Dumper \@arr;'