如何在php中执行file_get_contents后清除内存

I am trying to add certain variables to couple of files which already have some content.

I am using file_get_contents to copy the contents of a particular file and then using file_put_contents to paste variable values along with the existing contents to that file.

The problem is that, on the first instance it works properly but to the second file it pastes everything that has been stored in the memory. It puts all the contents from the first file along with the contents of the second file.

Is there any way that I can clear the memory before the next file_get_contents executes. Or my concept is false here.

Here is my code...

<?php

 if ($_POST["submit"]) {

    $ip = $_POST['ip'];
    $subnet = $_POST['subnet'];
    $gateway = $_POST['gateway'];
    $hostname = $_POST['hostname'];
    $domain = $_POST['domain'];
    $netbios = $_POST['netbios'];
    $password = $_POST['password'];


    $ipfile = 'one.txt';

    $file = fopen($ipfile, "r");
    $ipfileContents = fread($file, filesize($ipfile));

    $ipcontent = "ip='$ip'
";
    $ipcontent .= "netmask='$subnet'
";
    $ipcontent .= "gw='$gateway'
";
    $conten = $ipcontent . $ipfileContents;

    $file = fopen($ipfile, "w");
    fwrite($file, $ipfileContents);

    fclose($file);

    $ipsh = shell_exec('sh path/to/CHANGE_IP.sh');



    $hostfile = 'two.txt';

    $fileh = fopen($hostfile, "r");
    $hostfileContents = fread($fileh, filesize($hostfile));

    $hostcontent = "ip='$ip'
";
    $hostcontent .= "m_name='$hostname'
";
    $hostcontent .= "fqdn='$domain'
";
    $conten = $hostcontent . $hostfileContents;

    $fileh = fopen($hostfile, "w");
    fwrite($fileh, $hostfileContents);

    fclose($fileh);

$hostsh = shell_exec('sh path/to/MODIFY_HOSTS.sh');


}








?>

I have tried unset, but didn't work

$ipfilecontents->__destruct();
unset($ipfilecontents);

UPDATE:

file_get_contents & file_put_contents has some concurrency problems. So I had to change my method to fopen/fwrite/fclose and it worked flawlessly. Thanks for your help Jacinto.

        if ($_POST["submit"]) {

        $ip = $_POST['ip'];
        $subnet = $_POST['subnet'];
        $gateway = $_POST['gateway'];
        $hostname = $_POST['hostname'];
        $domain = $_POST['domain'];
        $netbios = $_POST['netbios'];
        $password = $_POST['password'];


        $ipfile = 'one.txt';

        $file = fopen($ipfile, "r");
        $ipfileContents = fread($file, filesize($ipfile));

        $ipcontent = "ip='$ip'
";
        $ipcontent .= "netmask='$subnet'
";
        $ipcontent .= "gw='$gateway'
";
        $content = $ipcontent . $ipfileContents;

        $file = fopen($ipfile, "w");
        fwrite($file, $content);

        fclose($file);

        $ipsh = shell_exec('sh path/to/CHANGE_IP.sh');

//do the same to the next file
}

This isn't an answer - I'll delete it in a minute. It's just a convenient place to show how to do trace statements:

    $ipfile = 'one.txt';
    $ipfileContents = file_get_contents($ipfile);
    $ipcontent = "ip='$ip'
";
    $ipcontent .= "netmask='$subnet'
";
    $ipcontent .= "gw='$gateway'
";
    echo "DEBUG: hostcontent=<pre>$ipcontent</pre><br />====<br />hostfileContents=<pre>$ipfileContents</pre><br />
";            
    file_put_contents($ipfile, $ipcontent . $ipfileContents,  LOCK_EX);
    $ipsh = shell_exec('sh path/to/CHANGE_IP.sh');

    $hostfile = 'two.txt';
    $hostfileContents = file_get_contents($hostfile);
    $hostcontent = "ip='$ip'
";
    $hostcontent .= "m_name='$hostname'
";
    $hostcontent .= "fqdn='$domain'
";
    echo "DEBUG: hostcontent=<pre>$hostcontent</pre><br />====<br />hostfileContents=<pre>$hostfileContents</pre><br />
";
    file_put_contents($hostfile, $hostcontent . $hostfileContents,  LOCK_EX);
    $hostsh = shell_exec('sh path/to/MODIFY_HOSTS.sh');

The most efficient would be to read and write the file in chunks simultaneously:

• open the file in read-write mode
• read the data chunk that will be overwritten by the new data
• reset pointer to begin of read chunk
• write new data
• make the read data the new data to be written
• repeat until there is no data to write

Example:

$bufw = "ip=''
";
$bufw .= "netmask=''
";
$bufw .= "gw=''
";

$bufw_len = strlen($bufw);

$file = fopen($ipfile, 'c+');
while ($bufw_len > 0) {
    // read next chunk
    $bufr = fread($file, $bufw_len);
    $bufr_len = strlen($bufr);

    // reset pointer to begin of chunk
    fseek($file, -$bufr_len, SEEK_CUR);

    // write previous chunk
    fwrite($file, $bufw);

    // update variables
    $bufw = $bufr;
    $bufw_len = strlen($bufw);
}
fclose($file);

With this the total memory usage is only up to the length of the new data to be written.

You can make it a function like:

function file_prepend_contents($filename, $data, $flags = 0, $context = null) {
    if (!is_null($context)) {
        $handle = fopen($filename, 'c+', ($flags & FILE_USE_INCLUDE_PATH) === FILE_USE_INCLUDE_PATH, $context);
    } else {
        $handle = fopen($filename, 'c+', ($flags & FILE_USE_INCLUDE_PATH) === FILE_USE_INCLUDE_PATH);
    }

    if (!$handle) return false;

    if (($flags & LOCK_EX) === LOCK_EX) {
        flock($handle, LOCK_EX);
    }

    $bytes_written = 0;

    $bufw = $data;
    $bufw_len = strlen($bufw);
    while ($bufw_len > 0) {
        // read next chunk
        $bufr = fread($handle, $bufw_len);
        $bufr_len = strlen($bufr);

        // reset pointer
        fseek($handle, -$bufr_len, SEEK_CUR);

        // write current chunk
        if (ftell($handle) === 0) {
            $bytes_written = fwrite($handle, $bufw);
        } else {
            fwrite($handle, $bufw);
        }

        // update variables
        $bufw = $bufr;
        $bufw_len = strlen($bufw);
    }
    fclose($handle);

    return $bytes_written;
}