Java regex to match quoted string with embedded escaped quote

Question

I need help with a regex for matching a quoted string that could have an embedded escaped quote.

For example, given string "'John\'s bike'". The basic pattern i was starting with, "'[^']*'", and expanding it to negate case of embedded escaped quotes using lookbehind doesn't work: "'((?<\\)[^'])*'".

Anyone has idea?

The string could be a series of quoted strings, e.g., "'John\'s bike', 'Mary\'s hat', 'my shoes'", and i want to tokenize each of the quoted substrings separately.

You have not demonstrated to us what your problem is sufficiently. Why can't you just use "'.*'" which captures your single test case. Demo here Do you not wish to capture `John\'s bike'? — Shawn Mehan
– Shawn Mehan, Commented Nov 11, 2015 at 22:36
Once you add the double quote as part of the regex "' .. '" you introduce a double delimiter. Not really too good. By double delim, I mean a delimiter that consists of 2 characters, that have open/close specific context. Like should "'hello\'" world match? — user557597
– user557597, Commented Nov 11, 2015 at 23:55

Pshemo · Accepted Answer · 2015-11-12 01:35:36Z

2

You can accept any character between quotes which is

preceded by \
not '.

So your regex can look like:

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

which in Java should look like "'(\\\\.|[^'])*'" (to create \ literal in regex we need to escape it like \\ but same rules applies in String literals so we need to escape these two \ again which finally gives us "\\\\")

Demo based on your example:

String input = "'John\\'s bike', 'Mary\\'s hat', 'my shoes'";
Pattern p = Pattern.compile("'(\\\\.|[^'])*'");
Matcher m = p.matcher(input);
while(m.find()){
    System.out.println(m.group());
}

Output:

'John\'s bike'
'Mary\'s hat'
'my shoes'

edited Nov 12, 2015 at 1:35

answered Nov 11, 2015 at 22:35

Pshemo

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8 Comments

mtkilbay Over a year ago

Why didn't i think of that? I was making it more complicated by explicitly looking for escaped backlash. Thank you!

mvallebr Over a year ago

this fails for \\". The regex "(\\\\[^\\\\]|[^\"])*" should do the trick.

Pshemo Over a year ago

@mvallebr What do you mean by fails? What \\" represents? IMO it represents escaped \ and not escaped " in which case we can consider that " as opening\closing quote (I am assuming that in your case " is quotation symbol, not ').

mvallebr Over a year ago

The original question said nothing about escaping back slashes. I never thought of it as a requirement. The requirement, for me, was solely escape quotes, nothing more.

Pshemo Over a year ago

So how exactly should foo\ be placed at the end of quote? If we write is as "...foo\" it will represent foo and escaped " so \ disappears (which is NOT what we want).

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