Question

I did not found a regex for my problem. There are always example-regex for escaping with back-slash.

But I need escaping by doubling the enclosing-character.

Example: ‘o”reilly’

Result: o’reilly

Answer 1

'(?:''|[^']*)*'

will match a quote-delimited string that may contain double-escaped quotes. So that’s your regex to find those strings.

Explanation:

'      # Match a single quote.
(?:    # Either match... (use (?> instead of (?: if you can)
 ''    # a doubled quote
|      # or
[^']*  # anything that's not a quote
)*     # any number of times.
'      # Match a single quote.

To now remove the quotes correctly, you could do it in two steps:

First, search for (?<!')'(?!') to find all single quotes; replace them with nothing.

Explanation:

(?<!') # Assert that the previous character (if present) isn't a quote
'      # Match a quote
(?!')  # Assert that the next character (if present) isn't a quote

Second, search for '' and replace all with '.