Regular Expressions - how to replace a character within quotes

Question

Hello regular expression experts,

There has never been a string manipulation problem I couldn\'t resolve with regular expressions until now, at least in an elegant m

Answer 1

Regular expressions are not particularly good at matching balanced text (i.e. starting and ending quotes).

A naïve approach would be to repeatedly apply something like this (until it no longer matched):

s/(^[^"]*(?:"[^"]*"[^"]*)*?)"([^",]*),([^"]*)"/$1"$2_$3"/

But that wouldn't work with escaped quotes. The best (i.e. simplest, most readable, and most maintanable) solution is to use a CSV file parser, go through all the field values one by one (replacing commas with underscores as you go), then write it back out to the file.