How to match regex over multiple lines [duplicate]

Question

I have a body of text and I am trying to find a character sequence within it. String.contains() will not work so Im trying to use String.matches method and a regular expression. My current regex isn't working. Here are my attempts:

"1stline\r\n2ndline".matches("(?im)^1stline$"); 
// returns false; I expect true

"1stline\r\n2ndline".matches("(?im)^1stline$") 
// returns false

"1stline\r\n2ndline\r\n3rdline".matches("(?im)^2ndline$")   

"1stline\n2ndline\n3rdline".matches("(?im)^2ndline$")

"1stline\n2ndline\n3rdline".matches("(?id)^2ndline$")

How should i format my regex so that it returns true?

Answer 1

You need to use the s flag (not the m flag).

It's called the DOTALL option.

This works for me:

  String input = "1stline\n2ndLINE\n3rdline";
  boolean b = input.matches("(?is).*2ndline.*");

I found it here.

Note you must use .* before and after the regex if you want to use String.matches().

That's because String.matches() attempts to match the entire string with the pattern.

(.* means zero or more of any character when used in a regex)

---

Another approach, found here:

  String input = "1stline\n2ndLINE\n3rdline";
  Pattern p = Pattern.compile("(?i)2ndline", Pattern.DOTALL);
  Matcher m = p.matcher(input);
  boolean b = m.find();
  print("match found: " + b);

I found it by googling "java regex multiline" and clicking the first result.

(it's almost as if that answer was written just for you...)

There's a ton of info about patterns and regexes here.

---

If you want to match only if 2ndline appears at the beginning of a line, do this:

   boolean b = input.matches("(?is).*\\n2ndline.*");

Or this:

 Pattern p = Pattern.compile("(?i)\\n2ndline", Pattern.DOTALL);