Index: src/org/jruby/RubyIO.java
===================================================================
--- src/org/jruby/RubyIO.java	(revision 2193)
+++ src/org/jruby/RubyIO.java	(arbetskopia)
@@ -859,11 +859,13 @@
         return getRuntime().newFixnum(0);
     }
 
+    private final static String LS = System.getProperty("line.separator");
+
     public IRubyObject puts(IRubyObject[] args) {
     	checkArgumentCount(args, 0, -1);
     	
         if (args.length == 0) {
-            callMethod("write", getRuntime().newString("\n"));
+            callMethod("write", getRuntime().newString(handler.getNewline()));
             return getRuntime().getNil();
         }
 
@@ -878,7 +880,7 @@
                 line = args[i].toString();
             }
             callMethod("write", getRuntime().newString(line+
-            		(line.endsWith("\n") ? "" : "\n")));
+            		(line.endsWith("\n") ? "" : handler.getNewline())));
         }
         return getRuntime().getNil();
     }
Index: src/org/jruby/util/IOHandlerSeekable.java
===================================================================
--- src/org/jruby/util/IOHandlerSeekable.java	(revision 2193)
+++ src/org/jruby/util/IOHandlerSeekable.java	(arbetskopia)
@@ -52,6 +52,11 @@
     protected RandomAccessFile file;
     protected String path;
     
+    private boolean shouldReplace = false;
+    private boolean isWin = true;
+
+    private String fileNewline;
+    
     public IOHandlerSeekable(IRuby runtime, String path, IOModes modes) 
     	throws IOException, InvalidValueException {
         super(runtime);
@@ -88,11 +93,23 @@
         if (modes.isAppendable()) {
             seek(0, SEEK_END);
         }
+        final String ls = System.getProperty("line.separator");
+        if(!modes.isBinary() && !"\n".equals(ls)) {
+            shouldReplace = true;
+            if("\r".equals(ls)) {
+                isWin = false;
+            }
+        }
+        fileNewline = ls;
 
         // We give a fileno last so that we do not consume these when
         // we have a problem opening a file.
         fileno = RubyIO.getNewFileno();
     }
+
+    public String getNewline() {
+        return fileNewline;
+    }
     
     public IOHandler cloneIOHandler() throws IOException, PipeException, InvalidValueException {
         IOHandler newHandler = new IOHandlerSeekable(getRuntime(), path, modes); 
@@ -233,7 +250,24 @@
      * @see org.jruby.util.IOHandler#sysread()
      */
     public int sysread() throws IOException {
-        return file.read();
+        if(!shouldReplace) {
+            return file.read();
+        } else {
+            final int curr = file.read();
+            if(curr != '\r') {
+                return curr;
+            } else if(!isWin) {
+                return '\n';
+            } else {
+                final int next = file.read();
+                if(next == '\n') {
+                    return next;
+                } else {
+                    file.seek(file.getFilePointer()-1);
+                    return curr;
+                }
+            }
+        }
     }
     
     /**
Index: src/org/jruby/util/IOHandler.java
===================================================================
--- src/org/jruby/util/IOHandler.java	(revision 2193)
+++ src/org/jruby/util/IOHandler.java	(arbetskopia)
@@ -201,6 +201,10 @@
      */
     public abstract void seek(long offset, int type) throws IOException, PipeException, InvalidValueException;
     public abstract void truncate(long newLength) throws IOException, PipeException;
+
+    public String getNewline() {
+        return "\n";
+    }
     
     public class PipeException extends Exception {
 		private static final long serialVersionUID = 1L;