As long as everyone's just chiming in with different ways, if you don't mind modifying the original array:

for (@temp) {
  push @a, $_ if s/^a_//;
  push @b, $_ if s/^b_//;
}
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You could even modify this to use a HoA-type solution, e.g.(update: fixed code..still untested):

my %hoa;
s/^([a-z])_// and push @{$hoa{$1}}, $_ for @temp;
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