Regex: How To Group The First Line, And Then Another Group With Everything else?

How can I write 开发者_开发技巧a regex that will put the first line in a group, and then everything else in a second group?

Depending on flavor, something like this should work: (?-s)(.*)(?s)(.*). This matches and captures (.*) twice, the first with "single-line" mode switched off, and the second with it switched on. You may even want to anchor the whole pattern within \A and \Z.

In Java:

String text =
    "first line\r" +
    "second line\r\n" +
    "third line etc";
System.out.println(
    text.replaceFirst(
        "(?-s)(.*)(?s)(.*)",
        "FIRST <<<$1>>>\nREST <<<$2>>>"
    )
);

This prints (as seen on ideone.com):

FIRST <<<first line>>>
REST <<<
second line
third line etc>>>

Depending on what you're actually doing (e.g. reading a file line by line), probably much better solution exists.

Since . does not match newline characters if you do not set the dotmatchesall (or singleline) flag, you can simply do

(.*)\r\n([\s\S]*)

Note that \r\n needs to be changed to whatever your files uses for its newline flag. That would be \n on Linux or \r on Macs (according to the Wikipedia).

/\A([^\n]*)\n(.*)\Z/s

This seems to work:

^(.*)$([\s\S]*)