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

Question

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

Answer 1

This seems to work:

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

Answer 2

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).

Answer 3

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

Answer 4

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.