Removing a line from the middle of a large file php

Question

I am trying to remove a line from the middle of a large file. ( > 20MB). I know the position in the file of the start of the line to be removed.

Here is what I currently have.

/**
 * Removes a line at a position from the file
 * @param  [int] $position  The position at the start of the line to be removed
 */
public function removeLineAt($position)
{
    $fp = fopen($this->filepath, "rw+");
    fseek($fp, $position);

    $nextLinePosition = $this->getNextLine($position, $fp);
    $lengthRemoved = $position - $nextLinePosition;
    $fpTemp = fopen('php://temp', "rw+");

    // Copy the bottom half (starting at line below the line to be removed)
    stream_copy_to_stream($fp, $fpTemp, -1, $nextLinePosition);

    // Seek to the start of the line to be removed
    fseek($fp, $position);
    rewind($fpTemp);

    // Copy the bottom half over the line to be removed
    stream_copy_to_stream($fpTemp, $fp);        

    fclose($fpTemp);
    fclose($fp);
}

However, while the code above does indeed remove the line from the file; since the temporary file is shorter than the original file. The tail end of the original file still exists and is doubled.

For Example: Original file was

1. a
2. b
3. c
4. d
5. e

The file after removing the line may look like

1. a
2. b
3. d
4. e
5. e

I have thought about somehow trimming the end of the main file by the $lengthRemoved amount however I can't think of an easy way to do that either.

Any suggestions?

• Note: The file has > 200,000 lines, sometimes > 300,000. I feel as if loading the entire file into an array (memory) would be pretty inefficient. Which is why I tried the above approach but ran into that one issue

---

For others who are looking for an answer here is the final function I came up with thanks to your help! Modify it to fit your needs.

/**
 * Removes a line at a position from the file
 * @param  [int] $position  The position at the start of the line to be removed
 */
public function removeLineAt($position)
{
    $fp = fopen($this->filepath, "rw+");
    fseek($fp, $position);

    $nextLinePosition = $this->getNextLine($position, $fp);
    $lengthRemoved = $position - $nextLinePosition;
    $fpTemp = fopen('php://temp', "rw+");

    // Copy the bottom half (starting at line below the line to be removed)
    stream_copy_to_stream($fp, $fpTemp, -1, $nextLinePosition);

    // Remove the difference
    $newFileSize = ($this->totalBytesInFile($fp) + $lengthRemoved);
    ftruncate($fp, $newFileSize);

    // Seek to the start of the line to be removed
    fseek($fp, $position);
    rewind($fpTemp);

    // Copy the bottom half over the line to be removed
    stream_copy_to_stream($fpTemp, $fp);        

    fclose($fpTemp);
    fclose($fp);
}

Answer 1

Since your file is very large you may want to use the sed command via exec if your php install will allow you to use that function.

exec("sed '3d' fileName.txt");

Where the 3 indicates the desired line number.

Answer 2

I think you are pretty close to a solution.

I would stick to your idea of removing the $lengthRemoved from the end of the file and would suggest to use ftruncate($handle, $size); before the fclose(), where size is the size to truncate to (size = originalFilesize - lengthRemoved).

http://www.php.net/manual/en/function.ftruncate.php