$ perl -E 'my ($s, $e) = qw{" "}; q{a"b"c} =~ /$s([^$e]*)/; say "|$1|"'
|b|
$ perl -E 'my ($s, $e) = qw{" "}; q{a""c} =~ /$s([^$e]*)/; say "|$1|"'
||
$ perl -E 'my ($s, $e) = qw{< >}; q{a<b>c} =~ /$s([^$e]*)/; say "|$1|"'
|b|
$ perl -E 'my ($s, $e) = qw{< >}; q{a<>c} =~ /$s([^$e]*)/; say "|$1|"'
||