Regex for splitting a string using space when not surrounded by single or double quotes

I'm new to regular expressions and would appreciate your help. I'm trying to put together an expression that will split the example string using all spaces that are not surrounded by single or double quotes. My last attempt looks like this: (?!") and isn't quite working. It's splitting on the space before the quote.

Example input:

This is a string that "will be" highlighted when your 'regular expression' matches something.

Desired output:

This
is
a
string
that
will be
highlighted
when
your
regular expression
matches
something.

Note that "will be" and 'regular expression' retain the space between the words.

Solution 1:

I don't understand why all the others are proposing such complex regular expressions or such long code. Essentially, you want to grab two kinds of things from your string: sequences of characters that aren't spaces or quotes, and sequences of characters that begin and end with a quote, with no quotes in between, for two kinds of quotes. You can easily match those things with this regular expression:

[^\s"']+|"([^"]*)"|'([^']*)'

I added the capturing groups because you don't want the quotes in the list.

This Java code builds the list, adding the capturing group if it matched to exclude the quotes, and adding the overall regex match if the capturing group didn't match (an unquoted word was matched).

List<String> matchList = new ArrayList<String>();
Pattern regex = Pattern.compile("[^\\s\"']+|\"([^\"]*)\"|'([^']*)'");
Matcher regexMatcher = regex.matcher(subjectString);
while (regexMatcher.find()) {
    if (regexMatcher.group(1) != null) {
        // Add double-quoted string without the quotes
        matchList.add(regexMatcher.group(1));
    } else if (regexMatcher.group(2) != null) {
        // Add single-quoted string without the quotes
        matchList.add(regexMatcher.group(2));
    } else {
        // Add unquoted word
        matchList.add(regexMatcher.group());
    }
} 

If you don't mind having the quotes in the returned list, you can use much simpler code:

List<String> matchList = new ArrayList<String>();
Pattern regex = Pattern.compile("[^\\s\"']+|\"[^\"]*\"|'[^']*'");
Matcher regexMatcher = regex.matcher(subjectString);
while (regexMatcher.find()) {
    matchList.add(regexMatcher.group());
} 

Solution 2:

There are several questions on StackOverflow that cover this same question in various contexts using regular expressions. For instance:

• parsings strings: extracting words and phrases
• Best way to parse Space Separated Text

UPDATE: Sample regex to handle single and double quoted strings. Ref: How can I split on a string except when inside quotes?

m/('.*?'|".*?"|\S+)/g 

Tested this with a quick Perl snippet and the output was as reproduced below. Also works for empty strings or whitespace-only strings if they are between quotes (not sure if that's desired or not).

This
is
a
string
that
"will be"
highlighted
when
your
'regular expression'
matches
something.

Note that this does include the quote characters themselves in the matched values, though you can remove that with a string replace, or modify the regex to not include them. I'll leave that as an exercise for the reader or another poster for now, as 2am is way too late to be messing with regular expressions anymore ;)

Solution 3:

If you want to allow escaped quotes inside the string, you can use something like this:

(?:(['"])(.*?)(?<!\\)(?>\\\\)*\1|([^\s]+))

Quoted strings will be group 2, single unquoted words will be group 3.

You can try it on various strings here: http://www.fileformat.info/tool/regex.htm or http://gskinner.com/RegExr/