You need to tell Perl that your string is multiple lines of text, using the "m" modifier:

my $text = qq{foo this is one example bar
this is a line I don't care about
foo here's another keeper! bar
foo yet another bar
and a line to reject};

foreach ($text =~ /^foo(.*)bar$/gm) {
  manipulate($_);
}

sub manipulate {
  print $_, "\n";
}
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(Note this assumes that foo and bar are going to be at the start and end of lines. It wasn't clear from your description whether "and a foo line to bar reject" should return nothing or "line to". Feel free to remove the ^ and $ to achieve the 2nd...)

Tony