Java change system new-line character

Question

On Windows, using System.out.println() prints out \n\r while on a Unix system you would get \n.

Is there any way to tell java what new-line characters you want to use?

Answer 1

As already stated by others, the system property line.separator contains the actual line separator. Strangely, the other answers missed the simple conclusion: you can override that separator by changing that system property at startup time.

E.g. if you run your program with the option -Dline.separator=X at the command line you will get the funny behavior of System.out.println(…); ending the line with an X.

The tricky part is how to specify characters like \n or \r at the command line. But that’s system/environment specific and not a Java question anymore.

Answer 2

Yes, there is a way and I've just tried it.

There is a system property line.separator. You can set it using System.setProperty("line.separator", whatever)

To be sure that it indeed causes JVM to use other separator I implemented the following exercise:

    PrintWriter writer = new PrintWriter(new FileWriter("c:/temp/mytest.txt"));
    writer.println("hello");
    writer.println("world");
    writer.close();

I am running on windows now, so the result was 14 bytes long file:

03/27/2014  10:13 AM                14 mytest.txt
               1 File(s)             14 bytes
               0 Dir(s)  409,157,980,160 bytes free

However when I added the following line to the beginning of my code:

    System.setProperty("line.separator", "\n");

I got 14 bytes long file:

03/27/2014 10:13 AM 14 mytest.txt 1 File(s) 14 bytes 0 Dir(s) 409,157,980,160 bytes free

I opened this file with notepad that does not recognize single \n as a new line and saw one-line text helloworld instead of 2 separate lines. So, this works.

Answer 3

Because the accepted answer simply does not work, as others pointed out before me, and the JDK only initialises the value once and then never reads the property anymore, only an internal static field, it became clear that the clean way to change the property is to set it on the command line when starting the JVM. So far, so good.

The reason I am writing yet another answer is that I want to present a reflective way to change the field, which really works with streams and writers relying on System.lineSeparator(). It does not hurt to update the system property, too, but the field is more important.

I know that reflection is ugly, as of Java 16+ needs an extra JVM command line parameter in order to allow it, and only works as long as the internals of System do not change in OpenJDK. But FWIW, here is my solution - don't do this at home, kids:

import java.io.*;
import java.lang.reflect.Field;
import java.nio.file.Files;

/**
 * 'assert' requires VM parameter '-ea' (enable assert)
 * 'Field.setAccessible' on System requires '--add-opens java.base/java.lang=ALL-UNNAMED' on Java 16+
 */
public class ChangeLineSeparator {
  public static void main(String[] args) throws IOException, NoSuchFieldException, IllegalAccessException {
    assert System.lineSeparator().equals("\r\n") : "default Windows line separator should be CRLF";
    Field lineSeparator = System.class.getDeclaredField("lineSeparator");
    lineSeparator.setAccessible(true);
    lineSeparator.set(null, "\n");
    assert System.lineSeparator().equals("\n") : "modified separator should be LF";

    File tempFile = Files.createTempFile(null, null).toFile();
    tempFile.deleteOnExit();
    try (PrintWriter out = new PrintWriter(new FileWriter(tempFile))) {
      out.println("foo");
      out.println("bar");
    }
    assert tempFile.length() == "foo\nbar\n".length() : "unexpected file size";
  }
}

Answer 4

You may try with:

String str = "\n\r";
System.out.print("yourString"+str);

but you can instead use this:-

System.getProperty("line.separator");

to get the line seperator

Returns the system-dependent line separator string. It always returns the same value - the initial value of the system property line.separator.

On UNIX systems, it returns "\n"; on Microsoft Windows systems it returns "\r\n".

Answer 5

As stated in the Java SE tutorial:

To modify the existing set of system properties, use System.setProperties. This method takes a Properties object that has been initialized to contain the properties to be set. This method replaces the entire set of system properties with the new set represented by the Properties object.

Warning: Changing system properties is potentially dangerous and should be done with discretion. Many system properties are not reread after start-up and are there for informational purposes. Changing some properties may have unexpected side-effects.

In the case of System.out.println(), the line separator that existed on system startup will be used. This is probably because System.lineSeparator() is used to terminate the line. From the documentation:

Returns the system-dependent line separator string. It always returns the same value - the initial value of the system property line.separator.

On UNIX systems, it returns "\n"; on Microsoft Windows systems it returns "\r\n".

As Holger pointed out, you need to overwrite this property at startup of the JVM.

Answer 6

Windows cmd: Credit jeb at https://superuser.com/a/1519790 for a technique to specify a line-feed character in a parameter using a cmd variable. This technique can be used to specify the java line.separator.

Here's a sample javalf.cmd file

@echo off

REM define variable %\n% to be the linefeed character
(set \n=^^^

^

)

REM Start java using the value of %\n% as the line.separator System property
java -Dline.separator=%\n% %1 %2 %3 %4 %5 %6 %7 %8 %9

Here's a short test progam.

public class ReadLineSeparator {
  public static void main(String... ignore) {
    System.out.println(System.lineSeparator().chars()
                       .mapToObj(c -> "{"+Character.getName(c)+"}")
                       .collect(java.util.stream.Collectors.joining()));
  }
}

On Windows, java ReadLineSeparator produces

{CARRIAGE RETURN (CR)}{LINE FEED (LF)}

.\javalf.cmd ReadLineSeparator produces

{LINE FEED (LF)}

Answer 7

The method System.lineSeparator() returns the line separator used by the system. From the documentation it specifies that it uses the system property line.separator.

Answer 8

Checked Java 11 implementation:

private static void initPhase1() {
    lineSeparator = props.getProperty("line.separator");
}

public static String lineSeparator() {
    return lineSeparator;
}

So altering system property at runtime doesn't change System.lineSeparator().

For this reason some projects re-read system property directly, see my answer: How to avoid CRLF (Carriage Return and Line Feed) in Logback - CWE 117

The only viable option is to set system property during app startup.

For Bash it is as simple as: java -Dline.separator=$'\n' -jar my.jar.

For POSIX shell it is better to save that character in some variable first:

LF='
'

java -Dline.separator="$LF" -jar my.jar

If you are not sure debug it:

printf %s "$LF" | wc -c
1

printf %s "$LF" | od -x
0000000 000a

For Gradle I use:

tasks.withType(Test).configureEach {
    systemProperty 'line.separator', '\n'
}

bootRun {
    systemProperty 'line.separator', '\n'
}