A field of a CSV file is a "single thing".
That "single thing" can be a single numeric value or a single string.
Concatenation of two fields can be complex if you mean to put that into a resulting CSV file.

"field1","field2"
could be?: ""field1""field2""
Or "field1field2"?

Use the Text::CSV_XS module to write fields which may contain quote characters. This quotes within quotes stuff can get complicated. Let the module do it. Again, A field of a CSV file is a "single thing".

update: Maybe I was not clear? Weird escaping rules can come into play when combining two text fields like "abc 123" and "xyz 456" into a single CSV field. The easiest way is "abc 123 xyz 456". However it is possible for the text field to have 2 separately identifiable quoted strings within it - that involves "quotes within quotes". If you want that, things get more complicated.