use warnings;
use strict;
use Data::Dumper;

my $string = "A dun dun B ignorable A something B\n";

my @contents = $string =~ /A (.*?) B/g;

print Dumper \@contents;
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Will output:

$VAR1 = [
          'dun dun',
          'something'
        ];
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With the key bits being the use of /g and assigning in list context.

If your strings can possibly overlap each other, then you've got more work to do, but it sounds like that is not the case here.