Pattern.UNIX_LINES in regex with Java

Question

Hi from the java doc here the following:

UNIX_LINES

public static final int UNIX_LINES

Enables Unix

Answer 1

_{I will try to explain it on . since same rule apply for ^ and $.}

Normally dot . matches every character except new line. In Unix only \n is new line mark, so other characters like carriage return \r are threated as normal characters.

Take a look at this String "A\r\nB\rC\nD". If you will try to find match for regex like.+ using

String data = "A\r\nB\rC\nD";
System.out.println(data);
Matcher m = Pattern.compile(".+").matcher(data);
while (m.find()) {
    System.out.println("["+m.group()+"]");
}

you will get

[A]
[B]
[C]
[D]

but if add flag Pattern.UNIX_LINES characters like \r will also be possible match for . and output will change into

[A
]
[B
C]
[D]

So first match is [A\r], second [B\rC] and third [C]