Regex for double quotes inside string

Question

A follow up to my previous question here. I realize I need to be more specific regarding my regex case to get an answer that works for my case.

I am fighting with this regex already for quite some time (also using the answers from my previous question) and I seem to be unable to build what I need.

I need to replace all occurrences of two recurring single quotes '' with \' inside all strings (so inside strings means between single quotes 'somesStringWithOrWithoutDoubleQuoteOccurrences'). It is because in one language (syntax) quotes within the string are escaped with a ' while the other (javascript) uses \ for escaping.

Here an example (the actual example can contains multiple strings separated with , but , can of course also appear withing the strings):

'word'''',and''','another'',''word','''test',X,'',FUNCTION('A'' B C D')
"--------------","----------------","------",-,"",FUNCTION("---------")
"    ++++    ++","       ++ ++    ","++    ", ,"",        (" ++      ")
     1 2     3           4  5        6                       7

result after replace should be:

'word\'\',and\'','another\',\'word','\'test',X,'',FUNCTION('A\' B C D')

++ is a required match the opening and closing quote in the string (represented by ") in line below the example should never be part of match (these single quotes mark the actual beginning or end of the string in which double quotes can appear).

It seems so simple when I see it, I can point out the double quotes immediately from the string but I am unable to get it properly defined inside my pattern.

---

Alternative

Another solution could be to replace the opening and closing quote with double quotes and replace the double occurrence of the single quite with a single single quote:

'word'''',and''','another'',''word','''test',X,'',FUNCTION('A'' B C D')
"--------------","----------------","------",-,"",FUNCTION("---------")
     ++++    ++ ,        ++ ++     , ++     , ,  ,        (  ++       )
     1 2     3           4  5        6                       7

result after replace in this case would be:

"word'',and'","another','word","'test",X,"",FUNCTION("A' B C D")

---

Here is a prepared Fiddle to test patterns

For what it helps I came up with not working:

/'(('{2})+)*'/g

and

/'[^']*(('')*)*[^']*'/g

and

/('(('{2})*)*')[^,$]/g

Answer 1

It is not a problem: just match these strings and use a replace callback method to replace double apostrophes with single ones:

var expression = /'([^']*(?:''[^']*)*)'/g;
var replacer = function(m, g1){
    return g1 ? "'" + g1.replace(/''/g, '\'') + "'" : "''";
}

See this updated fiddle

The '([^']*(?:''[^']*)*)' regex only matches the single quoted string literals capturing the contents in-between the single quotes.

Pattern matches:

• ' - leading single quote
• ([^']*(?:''[^']*)*) - Group 1 capturing any 0+ characters inside the '':
  • [^']* - 0+ characters other than a single quote
  • (?:''[^']*)* - 0+ sequences of:
  • '' - two consecutive apostrophes
  • [^']* - 0+ characters other than a single quote
• ' - closing single quote

So, when we perform the replacement, we check of Group 1 matches and is not empty. If it is, we just return '', and if not, we replace double apostrophes with single ones with the help of the "'" + g1.replace(/''/g, '\'') + "'" inside the replace callback.