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

Sunday, September 30, 2018

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

Answer

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.

Answer

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

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Sunday, September 30, 2018