I prefer to use \Q$var\E in regular expressions when I want to treat the variable's contents as a string (not interpret it is a regular expression). So I'd write:

@field_list = split /\Q$self->{delimiter}\E/, $field_line, -1;
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but you could also use quotemeta or structure it in several different ways.

I'll take a guess that your delimiter is "|".

                - tye