Find the first word and last few words in a string using regex

Question

Using these two regex expressions regPrefix and regSuffix,

final String POEM = "1. Twas brillig, and the slithy toves\n" + 
                    "2. Did gyre and gimble in the wabe.\n" +
                    "3. All mimsy were the borogoves,\n" + 
                    "4. And the mome raths outgrabe.\n\n";

String regPrefix = "(?m)^(\\S+)";   // for the first word in each line.
String regSuffix = "(?m)\\S+\\s+\\S+\\s+\\S+$";  // for the last 3 words in each line.
Matcher m1 = Pattern.compile(regPrefix).matcher(POEM);
Matcher m2 = Pattern.compile(regSuffix).matcher(POEM);

while (m1.find() && m2.find()) {
    System.out.println(m1.group() + " " + m2.group());
}

I am getting the correct output as:

1. the slithy toves
2. in the wabe.
3. were the borogoves,
4. mome raths outgrabe.

Is it possible to merge those two regex expressions into one, and get the same output? I tried something like:

String singleRegex = "(?m)^(\\S+)\\S+\\s+\\S+\\s+\\S+$";

but it didn't work for me.

May be, but this is for the purpose of learning complex regex. — Saurav Sahu, Sep 09 '18 at 04:37

Tim Biegeleisen · Accepted Answer · 2018-09-09T03:59:41.233

6

Use a single pattern with two capture groups:

String regex = "(?m)^(\\S+).*?((?:\\s+\\S+){3})$";
Matcher m = Pattern.compile(regex).matcher(POEM);
while (m.find()) {
    System.out.println(m.group(1) + m.group(2));
}

1. the slithy toves
2. in the wabe.
3. were the borogoves,
4. mome raths outgrabe.

Demo

edited Sep 09 '18 at 03:59

answered Sep 09 '18 at 03:53

Tim Biegeleisen

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Might consider `((?:\\s+\\S+){3})`, to repeat yourself less, and removing the need to concatenate a space in the `println` (assuming there aren't double-spaces at that point in the input there) – CertainPerformance Sep 09 '18 at 03:57
I don't know Java but I guess you can also do something like `m.replaceAll("$1 $2")`? – 41686d6564 stands w. Palestine Sep 09 '18 at 03:58
@CertainPerformance How on earth did you move to the top of the site in a few months? Well, I'm not surprised, given your good advice here. – Tim Biegeleisen Sep 09 '18 at 04:00
@SauravSahu It's called a [non-capturing group](https://stackoverflow.com/q/3512471/4934172). – 41686d6564 stands w. Palestine Sep 09 '18 at 04:03

Find the first word and last few words in a string using regex

1 Answers1

Demo