Append a line at the beginning of a file via UTL_FILE

Hello,
is there a way to append a line to the beginning of a file instead of at the end of an existing file via UTL_FILE?
Thanks in advance,
Geert

No, you would have to create a new file.

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Insert a line into the beginning of a file without overwriting data

I would like to dynamically alter/add new headers to a csv file as needed. The code I have below overwrites the previously written data an amount equal to each new header added each time I call the vi below. Any suggestions on how to do this without reading in the file each time? I want to avoid the processing time of reading in the file between processing new data.
Thanks!
Attachments:
R900 - Log Data Stream to File.vi ‏22 KB

Yes, but you can still write everytime, you dont need to read the file back.
/Y
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Hello,
I am trying to append a character to the beginning of a file, doesnt seem to work with RandomFileAccess. I first called the seek() methond
seek(0); //zero to send the file pointer to the front
write((byte) myCharValue);apparently it overwrites the value at the front instead of adding for example:
before running the code the file has: "Java is Cool!"
after running the code the file has: "xava is Cool!"
Any Ideas?
Thanks

1. Create a new file.
2. Write out whatever you wanted to insert at the beginning.
3. Copy the data from the old file and append it to the new file.
4. Close the files.
5. Delete the old file.
6. Rename the new file.

How to remove characters/lines from the beginning of an InputStream

Hi,
I have a program which receives several InputStreams. From each of these streams I have to remove 2 lines from the beginning. After the lines are removed, all the streams are combined to one with SequenceInputStream and read in one chunk. Is there an easy/simple way of doing this?
One option I thought would be to read the char by char until 2 end of line chars have been detected and then read the rest of the data to a buffer. And the create a ByteArrayInputStream out of this buffer. Problem with this approach is, that the amount of data can be large, so putting all the data in to memory might cause problems.
Another option is to use BufferredInputStream and use the readline() method twice to get rid of the lines that are not needed. After this I would write the data to some output stream, which is then converted back to input stream. Propably would work, but sound too much of work for a simple thing like this. There has to be better way.
To make it simple, what I need is a method that looks like the following, or something similar
* Removes n number of lines from the beginning of a InputStream.
* @param is InputStream where the lines are removed
* @param numberOfLines int value to indicate how many lines whould be removed
* @return InputStream where lines have been removed.
public InputStream removeLines(InputStream is, numberOfLines);Thanks.

Here's the code, feel free to use it. Comments are also welcome.
public InputStream removeLinesFromTheBeginning(InputStream is, int numberOfLines) throws IOException
 char c = 'c';
 int i = 0;
 for(int n = 0 ; n < numberOfLines ; n++)
 do
 c = (char)is.read();
 System.out.print(c);
 if(c == (char)-1) // end of stream reached before any newline characters were found.
 return null;
 i++;
 while(c != '\n');
 System.out.println();
 System.out.println("Characters removed:" + i);
 System.out.println("n: " + n);
 i = 0;
 return is;
 }Edited by: dave_spaghetti on Jun 16, 2009 5:42 AM
Fixed a bug.

Add a new line at the begining of a string in a Xquery ALSB3.0

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How would I erase the beginning of a file?

I want to be able to erase the beginning of a file, while writing to the end...WITHOUT reading the whole file and writing it again because that would be a waste of resourses. Obviously I know that option is available.
My situation is that I am adding lines to a log file, and I want to remove any entries that are X hours old. Logging a lot of information would mean that every few seconds, an entry is older than X hours and needs to be removed. It doesnt have a set number of lines so I can't just recycle the file by doing something like: if at line number Y, start at line 1 and remember the current line number.
Adding to the top of the file, pushing the others lines down, and making cuts at the end would also work, but the same situation arises, how do I add to the beginning of the file, without having to copy the entire file to add the entry to the top.
The reason I don't want to read the whole file is because having to read the whole file and write the whole file when an entry is made is time consuming and wastes CPU and memory, especially when the logs are coming in several lines a second.

I would think it could easily be done. say you want to erase the first 10 bytes, why cant you just say move the start of the file up 10 bytes. Somewhere in the filesystem the start of the file is stored. I found underlying file copying that claims this in FileChannel's transferTo and transferFrom:
This method is potentially much more efficient than a simple loop that reads from this channel and writes to the target channel. Many operating systems can transfer bytes directly from the filesystem cache to the target channel without actually copying them.
If I can't just chop, I'll have to copy quickly at scheduled intervals.
This is code I ran to test the above quote:
    public static void main(String[] args) throws Exception{
        args = new String[2];
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter File Name:");
        args[0] = input.readLine();
        System.out.println("Enter test (0-2):");
        args[1] = input.readLine();
        long time = System.currentTimeMillis();
        int version = Integer.parseInt(args[1]);
        switch (version) {
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                BufferedReader in = new BufferedReader(new FileReader(args[0]));
                PrintWriter out = new PrintWriter(new FileWriter("tempfile.txt"));
                in.readLine();//skip line.
                for (String line = in.readLine();line != null;line = in.readLine()) {
                    out.println(line);
                in.close();
                out.close();
                break;
            case 1:
                RandomAccessFile raf = new RandomAccessFile(args[0],"rw");
                String line = raf.readLine();
                long offset = raf.getFilePointer();
                byte[] b = new byte[1024];
                int bytes = 1024;
                long index = 0;
                System.out.println("index = " + raf.getFilePointer());
                System.out.println("index = " + line.length());
                while(bytes == 1024) {
                    bytes = raf.read(b);
                    index = raf.getFilePointer();
                    raf.seek(index - bytes - offset);
                    raf.write(b,0,bytes);
                    raf.seek(index);
                raf.setLength(raf.length()-offset);
                raf.close();
                break;
            case 2:
                RandomAccessFile raf2 = new RandomAccessFile(args[0],"rw");
                String line2 = raf2.readLine();
                long offset2 = raf2.getFilePointer();
                FileChannel f = raf2.getChannel();
                FileChannel g = f.position(0);
                g.transferTo(offset2,raf2.length() - offset2,f);
                raf2.setLength(raf2.length()-offset2);
                raf2.close();
                break;
        System.out.println(System.currentTimeMillis() - time);
    }and had these results
166MB Log File
Linux Mandrake 900Mhz
Case 0 = 32914 ms
Case 1 (1k byte[]) = 15043 ms
Case 1 (16k byte[]) = 6988 ms
Case 1 (1MB byte[] = 6113 ms
Case 2 = 6188 ms
:-/ guess this proves that the FileChannel can't chop

How to delete the beginning of a file?

Hi,
is there a way to delete the beginning of a file, or do I have to copy the rest of the file and create a new one and then delete the old one?
Lets say my file contains "ThisIsMyFile" and I want to delete "This", so that my new file contains "IsMyFile", how can I do this?
thanx

You have to copy.

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Hi All,
I have a table1 with a field zip of varchar2 type
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33174
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Hi,
Well, you can even concatenate a zero at the beginning as a where clause is used in the UPDATE statement which is restricting the update to happen on only those rows which are of 4 character length.
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' �� '
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Thanks
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While reading and validating a file in Java, HOW can I
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Thanks in advance,
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application 1 prints this to a file:
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There is a particular case with sugested function, if content is generated on the fly by the server -php, cgi, etc.-
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ÿØÿà JFIF
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Append a line at the beginning of a file via UTL_FILE

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