Regex for quoted string with escaping quotes

/"(?:[^"\\]|\\.)*"/

Works in The Regex Coach and PCRE Workbench.

Example of test in JavaScript:

    var s = ' function(){ return " Is big \\"problem\\", \\no? "; }';
    var m = s.match(/"(?:[^"\\]|\\.)*"/);
    if (m != null)
        alert(m);

This one comes from nanorc.sample available in many linux distros. It is used for syntax highlighting of C style strings

\"(\\.|[^\"])*\"

/(["\']).*?(?<!\\)(\\\\)*\1/is

should work with any quoted string

"(?:\\"|.)*?"

Alternating the \" and the . passes over escaped quotes while the lazy quantifier *? ensures that you don't go past the end of the quoted string. Works with .NET Framework RE classes

An option that has not been touched on before is:

1. Reverse the string.
2. Perform the matching on the reversed string.
3. Re-reverse the matched strings.

This has the added bonus of being able to correctly match escaped open tags.

Lets say you had the following string; String \"this "should" NOT match\" and "this \"should\" match" Here, \"this "should" NOT match\" should not be matched and "should" should be. On top of that this \"should\" match should be matched and \"should\" should not.

First an example.

// The input string.
const myString = 'String \\"this "should" NOT match\\" and "this \\"should\\" match"';

// The RegExp.
const regExp = new RegExp(
    // Match close
    '([\'"])(?!(?:[\\\\]{2})*[\\\\](?![\\\\]))' +
    '((?:' +
        // Match escaped close quote
        '(?:\\1(?=(?:[\\\\]{2})*[\\\\](?![\\\\])))|' +
        // Match everything thats not the close quote
        '(?:(?!\\1).)' +
    '){0,})' +
    // Match open
    '(\\1)(?!(?:[\\\\]{2})*[\\\\](?![\\\\]))',
    'g'
);

// Reverse the matched strings.
matches = myString
    // Reverse the string.
    .split('').reverse().join('')
    // '"hctam "\dluohs"\ siht" dna "\hctam TON "dluohs" siht"\ gnirtS'

    // Match the quoted
    .match(regExp)
    // ['"hctam "\dluohs"\ siht"', '"dluohs"']

    // Reverse the matches
    .map(x => x.split('').reverse().join(''))
    // ['"this \"should\" match"', '"should"']

    // Re order the matches
    .reverse();
    // ['"should"', '"this \"should\" match"']

Okay, now to explain the RegExp. This is the regexp can be easily broken into three pieces. As follows:

# Part 1
(['"])         # Match a closing quotation mark " or '
(?!            # As long as it's not followed by
  (?:[\\]{2})* # A pair of escape characters
  [\\]         # and a single escape
  (?![\\])     # As long as that's not followed by an escape
)
# Part 2
((?:          # Match inside the quotes
(?:           # Match option 1:
  \1          # Match the closing quote
  (?=         # As long as it's followed by
    (?:\\\\)* # A pair of escape characters
    \\        # 
    (?![\\])  # As long as that's not followed by an escape
  )           # and a single escape
)|            # OR
(?:           # Match option 2:
  (?!\1).     # Any character that isn't the closing quote
)
)*)           # Match the group 0 or more times
# Part 3
(\1)           # Match an open quotation mark that is the same as the closing one
(?!            # As long as it's not followed by
  (?:[\\]{2})* # A pair of escape characters
  [\\]         # and a single escape
  (?![\\])     # As long as that's not followed by an escape
)

This is probably a lot clearer in image form: generated using Jex's Regulex

Image on github (JavaScript Regular Expression Visualizer.) Sorry, I don't have a high enough reputation to include images, so, it's just a link for now.

Here is a gist of an example function using this concept that's a little more advanced: https://gist.github.com/scagood/bd99371c072d49a4fee29d193252f5fc#file-matchquotes-js

One has to remember that regexps aren't a silver bullet for everything string-y. Some stuff are simpler to do with a cursor and linear, manual, seeking. A CFL would do the trick pretty trivially, but there aren't many CFL implementations (afaik).

A more extensive version of https://stackoverflow.com/a/10786066/1794894

/"([^"\\]{50,}(\\.[^"\\]*)*)"|\'[^\'\\]{50,}(\\.[^\'\\]*)*\'|“[^”\\]{50,}(\\.[^“\\]*)*”/   

This version also contains

1. Minimum quote length of 50
2. Extra type of quotes (open “ and close ”)

If your IDE is IntelliJ Idea, you can forget all these headaches and store your regex into a String variable and as you copy-paste it inside the double-quote it will automatically change to a regex acceptable format.

example in Java:

String s = "\"en_usa\":[^\\,\\}]+";

now you can use this variable in your regexp or anywhere.