PHP - insert at specific location

lets say you have a file where you want to insert a string into an existing file at a specific location.
put a key into the file where you want the new text appear, i.e.:

###INSERTHERE###

then use this function to insert the new data at this keypoint

insert at specific location” makes use of the built-in PHP functions file_exists( ), is_writeable( ), filesize( ), clearstatcache( ), fopen( ), fread( ), strpos( ), fclose( ), ftruncate( ), strtr( ) and fwrite( ).

<?php

/* Description:
| lets say you have a file where you want to insert a string into an existing file
| at a specific location. put a key into the file where you want the new text
| appear, i.e.: ###INSERTHERE### then use this function to insert the new data at
| this keypoint
|
------------------------------------------------------------------------------*/



/*------------------------------------
| function insert_string_in_file
|
| expects: $file          - required [path] to the file you want to work with
|          $insert_point  - required [string] which should be acted on
|          $string        - required [string] which should be inserted
|          $return        - optional [bool] returns message if true, true|false if not
|          $position      - optional [string] before|after - default is replace
|
| returns: [string] with status message
|
|-----------------------------------*/
function insert_string_in_file($file,$insert_point,$string,$return=FALSE,$position='')
{
    // check if file exists
    if(!file_exists($file))
    {
        return($return === TRUE ? 'ERROR - file ('.$file.') does not exist' : FALSE);
    }
    // check if file is writeable
    if(!is_writeable($file))
    {
        return($return === TRUE ? 'ERROR - file ('.$file.') is not writeable' : FALSE);
    }
    // contruct insertion scheme
    if(empty($position))
    {
        // if nothing specified, replace the insertion point with string
        $replacement[$insert_point] = $string;
    }else{
        if($position == 'before')
        {
            // insert the string before the insertion point
            $replacement[$insert_point] = $string.$insert_point;
        }elseif($position == 'after')
        {
            // insert the string after the insertion point
            $replacement[$insert_point] = $insert_point.$string;
        }else{
            return($return === TRUE ? 'ERROR - position ('.$position.') is invalid -
                    use &quot;before&quot; or &quot;after&quot;' : FALSE);
        }
    }
    // check filelenght
    $filesize = filesize($file);
    clearstatcache();
    if($filesize == 0)
    {
        return ($return === TRUE ? 'ERROR - file ('.$file.') is empty' : FALSE);   
    }
    // open file for read and write access
    if(!$handle = fopen($file, 'r+'))
    {
        return($return === TRUE ? 'ERROR - cannot open file ('.$file.')' : FALSE);
    }else{
        $old_contents = fread($handle, $filesize);
    }
    // insert string at the insertion point
    if(!strpos($old_contents,$insert_point))
    {
        fclose($handle);
        return($return === TRUE ? 'ERROR - insertion point ('.$insert_point.') not found' : FALSE);
    }else{
        ftruncate($handle,0);
        $new_contents = strtr($old_contents,$replacement);
    }
    // write new content to file
    if(fwrite($handle, $new_contents) === FALSE)
    {
        fclose($handle);
        return ($return === TRUE ? 'ERROR - cannot write to file ('.$file.')' : FALSE);
    }
    fclose($handle);
    return($return === TRUE ? 'SUCCESS - your string was inserted' : TRUE);
}

// use like
$the_file = 'path/to/file.txt';
$insert_key = '###INSERTHERE###';

$new_data = ' your text to insert';

// insert string before insertion point and get verbose messages
echo insert_string_in_file($the_file,$insert_key,$new_data,TRUE,'before').'<br />';

$new_data = ' should be here';

// simply replace insertion point
if(insert_string_in_file($the_file,$insert_key,$new_data))
{
    echo $insert_key.' was replaced by '.$new_data.' in the file '.$the_file.'.';
}else{
    echo 'insertion failed<br />';
}

?>