Java pattern regex with escape characters

Question

I want to replace ";" with "\n" except when it's escaped with a leading '\'. I haven't figured out the correct regex.

Here is what I have:

String s = "abc;efg\\;hij;pqr;xyz\\;123"
s.replaceAll("\\[^\\\\];", "\\\\n");

I'd expect the above string to be replaced with "abc\nefg\;hij;pqr;xyz\;123"

I don't want to replace \; with \n. Only the semicolons with new line. I fixed the regex above. — Darth Ninja
– Darth Ninja, Commented Apr 5, 2016 at 3:48
So, @DarthNinja, when you said "I want to replace '\;' with '\n'" -- you didn't mean that...is that right? Ask the question you mean, please. — Jan Nielsen
– Jan Nielsen, Commented Apr 5, 2016 at 3:53
@Darth what about the other semicolons - after "hij" and "pqr"? Or do you only want the first semicolon to be replaced? — Bohemian
– Bohemian ♦, Commented Apr 5, 2016 at 3:53
All unescaped semicolons to be replaced with new line. Any \; should be excluded. — Darth Ninja
– Darth Ninja, Commented Apr 5, 2016 at 3:55

Bohemian · Accepted Answer · 2016-04-05 03:58:04Z

2

Use a negative look behind:

s = s.replaceAll("(?<!\\\\);", "\n");

The expression (?<!\\) (coded as a java string literal "(?<!\\\\)") means "the previous character should not be a backslash"

Test code:

String s = "abc;efg\\;hij;pqr;xyz\\;123";
s = s.replaceAll("(?<!\\\\);", "\n");
System.out.println(s);

Output:

abc
efg\;hij
pqr
xyz\;123

answered Apr 5, 2016 at 3:52

Bohemian♦

427k103 gold badges603 silver badges750 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1