How to use beginning and endline markers in regex for Java String?

Question

Why doesn\'t the following change the text for me in Android?

String content = \"test\\n=test=\\ntest\";
content = content.replaceAll(\"^=(.+)=$\", \"

        

Answer 1

In Java String objects \n isn't considered a beginning of a line or an end of a line. It's a line feed. To match this, you need to change your code to

String content = "test\n=test=\ntest";
content = content.replaceAll("\n=(.+)=\n", "\n$1\n");

What ^ and $ match, are the beginning and the end of the String object itself.

If you're reading from a file, the newline could be a CRLF character in which case you want to match \r too. In that case you need to use a regex like this

content = content.replaceAll("[\n\r]=(.+)=[\n\r]", "\n$1\n");

If you need to match to work in multiple instances in multiple 'lines' in the same String, you should first split the String to multiple lines.

String content = "test\n=test=\n=test=\ntest";
String[] pieces = content.split("[\r\n]");
StringBuilder replaced = new StringBuilder();

for (int i=0; i$1");
    replaced.append(piece);
    replaced.append('\n');
}