Note - using fopen in 'w' mode will NOT update the modification time (filemtime) of a file like you may expect. You may want to issue a touch() after writing and closing the file which update its modification time. This may become critical in a caching situation, if you intend to keep your hair.

/***** GENTLE REMINDER *****/
Really important. Do NOT use the "w" flag unless you want to delete everything in the file.

Note that for fopen() to create files when called with such mode, the path you have given needs to exist as fopen() cannot create directories; but only files it can create. This is normal behavior.

<?php

// Write log file, create if not exists
$log = fopen('/var/logs/someapp/error.log', 'wb');
// This will silently fail if /var/logs/someapp directory doesn't exist

?>

The verbal descriptions take a while to read through to get a feel for the expected results for fopen modes. This csv table can help break it down for quicker understanding to find which mode you are looking for:

Mode,Creates,Reads,Writes,Pointer Starts,Truncates File,Notes,Purpose
r,,y,,beginning,,fails if file doesn't exist,basic read existing file
r+,,y,y,beginning,,fails if file doesn't exist,basic r/w existing file
w,y,,y,beginning+end,y,,"create, erase, write file"
w+,y,y,y,beginning+end,y,,"create, erase, write file with read option"
a,y,,y,end,,,"write from end of file, create if needed"
a+,y,y,y,end,,,"write from end of file, create if needed, with read options"
x,y,,y,beginning,,fails if file exists,"like w, but prevents over-writing an existing file"
x+,y,y,y,beginning,,fails if file exists,"like w+, but prevents over writing an existing file"
c,y,,y,beginning,,,open/create a file for writing without deleting current content
c+,y,y,y,beginning,,,"open/create a file that is read, and then written back down"

With php 5.2.5 on Apache 2.2.4, accessing files on an ftp server with fopen() or readfile() requires an extra forwardslash if an absolute path is needed.

i.e., if a file called bullbes.txt is stored under /var/school/ on ftp server example.com and you're trying to access it with user blossom and password buttercup, the url would be:

ftp://blossom:[email protected]//var/school/bubbles.txt

Note the two forwardslashes. It looks like the second one is needed so the server won't interpret the path as relative to blossom's home on townsville.

There is an undocumented mode for making fopen non-blocking (not working on windows). By adding 'n' to the mode parameter, fopen will not block, however if the pipe does not exist an error will be raised.

$fp = fopen("/tmp/debug", "a"); //blocks if pipe does not exist

$fp = fopen("/tmp/debug", "an"); //raises error on pipe not exist

Note that whether you may open directories is operating system dependent. The following lines:

<?php
// Windows ($fh === false)
$fh = fopen('c:\\Temp', 'r');

// UNIX (is_resource($fh) === true)
$fh = fopen('/tmp', 'r');
?>

demonstrate that on Windows (2000, probably XP) you may not open a directory (the error is "Permission Denied"), regardless of the security permissions on that directory.

On UNIX, you may happily read the directory format for the native filesystem.

fopen() will block if the file to be opened is a fifo. This is true whether it's opened in "r" or "w" mode.  (See man 7 fifo: this is the correct, default behaviour; although Linux supports non-blocking fopen() of a fifo, PHP doesn't).
The consequence of this is that you can't discover whether an initial fifo read/write would block because to do that you need stream_select(), which in turn requires that fopen() has happened!

<?php
#going to update last users counter script since
#aborting a write because a file is locked is not correct.

$counter_file = '/tmp/counter.txt';
clearstatcache();
ignore_user_abort(true);     ## prevent refresh from aborting file operations and hosing file
if (file_exists($counter_file)) {
   $fh = fopen($counter_file, 'r+');
    while(1) {
      if (flock($fh, LOCK_EX)) {
         #$buffer = chop(fgets($fh, 2));
         $buffer = chop(fread($fh, filesize($counter_file)));
         $buffer++;
         rewind($fh);
         fwrite($fh, $buffer);
         fflush($fh);
         ftruncate($fh, ftell($fh));     
         flock($fh, LOCK_UN);
         break;
      }
   }
}
else {
   $fh = fopen($counter_file, 'w+');
   fwrite($fh, "1");
   $buffer="1";
}
fclose($fh);

print "Count is $buffer";

?>

While opening a file with multibyte data (Ex: données multi-octets), faced some issues with the encoding. Got to know that it uses  windows-1250. Used iconv to convert it to UTF-8 and it resolved the issue.  

<?php
function utf8_fopen_read($fileName) {
    $fc = iconv('windows-1250', 'utf-8', file_get_contents($fileName)); 
    $handle=fopen("php://memory", "rw");
    fwrite($handle, $fc); 
    fseek($handle, 0); 
    return $handle;
}
?>

Example usage:

<?php
$fh = utf8_fopen_read("./tpKpiBundle.csv");
while (($data = fgetcsv($fh, 1000, ",")) !== false) {
    foreach ($data as $value) {
        echo $value . "<br />\n";
    }
}
?>

Hope it helps.

This functions check recursive permissions and recursive existence parent folders, before creating a folder. To avoid the generation of errors/warnings. 

/**
 * This functions check recursive permissions and recursive existence parent folders,
 * before creating a folder. To avoid the generation of errors/warnings. 
 *
 * @return bool
 *     true folder has been created or exist and writable. 
 *     False folder not exist and cannot be created. 
 */
function createWritableFolder($folder)
{
    if (file_exists($folder)) {
        // Folder exist.
        return is_writable($folder);
    }
    // Folder not exit, check parent folder.
    $folderParent = dirname($folder);
    if($folderParent != '.' && $folderParent != '/' ) {
        if(!createWritableFolder(dirname($folder))) {
            // Failed to create folder parent.
            return false;
        }
        // Folder parent created.
    }

    if ( is_writable($folderParent) ) {
        // Folder parent is writable.
        if ( mkdir($folder, 0777, true) ) {
            // Folder created.
            return true;
        }
        // Failed to create folder.
    }
    // Folder parent is not writable.
    return false;
}

/**
 * This functions check recursive permissions and recursive existence parent folders,
 * before creating a file/folder. To avoid the generation of errors/warnings. 
 *
 * @return bool
 *     true has been created or file exist and writable. 
 *     False file not exist and cannot be created. 
 */
function createWritableFile($file)
{
    // Check if conf file exist.
    if (file_exists($file)) {
        // check if conf file is writable.
        return is_writable($file);
    }

    // Check if conf folder exist and try to create conf file.
    if(createWritableFolder(dirname($file)) && ($handle = fopen($file, 'a'))) {
        fclose($handle);
        return true; // File conf created.
    }
    // Inaccessible conf file.
    return false;
}

i had to do such function to display newest log entries on top to be displayed in browser
its easy to adjust it from anonymous to normal function and/or add content on end
most important is same log can be used by many threads/processes (Swoole, ReactPHP, php_fpm)
also it had to keep reasonable size to load fast

$prependFileThreadSafe = static function (string $file, string $content, int $maxLen = 1024*500): void {
    $f = fopen($file, 'c+');
    flock($f, LOCK_EX);
    $prev = fread($f, $maxLen-strlen($content));
    fseek($f, 0);
    fwrite($f, $content . $prev);
    flock($f, LOCK_UN);
    fclose($f);
};

usage:
$prependFileThreadSafe('my.log', "some content\n");

I couldn't for the life of me get a certain php script working when i moved my server to a new Fedora 4 installation. The problem was that fopen() was failing when trying to access a file as a URL through apache -- even though it worked fine when run from the shell and even though the file was readily readable from any browser.  After trying to place blame on Apache, RedHat, and even my cat and dog, I finally ran across this bug report on Redhat's website:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=164700

Basically the problem was SELinux (which I knew nothing about) -- you have to run the following command in order for SELinux to allow php to open a web file:

/usr/sbin/setsebool httpd_can_network_connect=1

To make the change permanent, run it with the -P option:

/usr/sbin/setsebool -P httpd_can_network_connect=1

Hope this helps others out -- it sure took me a long time to track down the problem.

Simple class to fetch a HTTP URL. Supports "Location:"-redirections. Useful for servers with allow_url_fopen=false. Works with SSL-secured hosts.

<?php
#usage:
$r = new HTTPRequest('http://www.example.com');
echo $r->DownloadToString();

class HTTPRequest
{
    var $_fp;        // HTTP socket
    var $_url;        // full URL
    var $_host;        // HTTP host
    var $_protocol;    // protocol (HTTP/HTTPS)
    var $_uri;        // request URI
    var $_port;        // port
    
    // scan url
    function _scan_url()
    {
        $req = $this->_url;
        
        $pos = strpos($req, '://');
        $this->_protocol = strtolower(substr($req, 0, $pos));
        
        $req = substr($req, $pos+3);
        $pos = strpos($req, '/');
        if($pos === false)
            $pos = strlen($req);
        $host = substr($req, 0, $pos);
        
        if(strpos($host, ':') !== false)
        {
            list($this->_host, $this->_port) = explode(':', $host);
        }
        else 
        {
            $this->_host = $host;
            $this->_port = ($this->_protocol == 'https') ? 443 : 80;
        }
        
        $this->_uri = substr($req, $pos);
        if($this->_uri == '')
            $this->_uri = '/';
    }
    
    // constructor
    function HTTPRequest($url)
    {
        $this->_url = $url;
        $this->_scan_url();
    }
    
    // download URL to string
    function DownloadToString()
    {
        $crlf = "\r\n";
        
        // generate request
        $req = 'GET ' . $this->_uri . ' HTTP/1.0' . $crlf
            .    'Host: ' . $this->_host . $crlf
            .    $crlf;
        
        // fetch
        $this->_fp = fsockopen(($this->_protocol == 'https' ? 'ssl://' : '') . $this->_host, $this->_port);
        fwrite($this->_fp, $req);
        while(is_resource($this->_fp) && $this->_fp && !feof($this->_fp))
            $response .= fread($this->_fp, 1024);
        fclose($this->_fp);
        
        // split header and body
        $pos = strpos($response, $crlf . $crlf);
        if($pos === false)
            return($response);
        $header = substr($response, 0, $pos);
        $body = substr($response, $pos + 2 * strlen($crlf));
        
        // parse headers
        $headers = array();
        $lines = explode($crlf, $header);
        foreach($lines as $line)
            if(($pos = strpos($line, ':')) !== false)
                $headers[strtolower(trim(substr($line, 0, $pos)))] = trim(substr($line, $pos+1));
        
        // redirection?
        if(isset($headers['location']))
        {
            $http = new HTTPRequest($headers['location']);
            return($http->DownloadToString($http));
        }
        else 
        {
            return($body);
        }
    }
}
?>

a variable $http_response_header is available when doing the fopen(). Which contains an array of the response header.

PHP will open a directory if a path with no file name is supplied. This just bit me. I was not checking the filename part of a concatenated string.

For example:

<?php
$fd = fopen('/home/mydir/' . $somefile, 'r');
?>

Will open the directory if $somefile = ''

If you attempt to read using the file handle you will get the binary directory contents. I tried append mode and it errors out so does not seem to be dangerous.

This is with FreeBSD 4.5 and PHP 4.3.1. Behaves the same on 4.1.1 and PHP 4.1.2. I have not tested other version/os combinations.

I was working on a consol script for win32 and noticed a few things about it.  On win32 it appears that you can't re-open the input stream for reading, but rather you have to open it once, and read from there on.  Also, i don't know if this is a bug or what but it appears that fgets() reads until the new line anyway.  The number of characters returned is ok, but it will not halt reading and return to the script.  I don't know of a work around for this right now, but i'll keep working on it.

This is some code to work around the close and re-open of stdin.

<?php
function read($length='255'){
    if (!isset($GLOBALS['StdinPointer'])){
        $GLOBALS['StdinPointer']=fopen("php://stdin","r");
    }
    $line=fgets($GLOBALS['StdinPointer'],$length);
    return trim($line);
}
echo "Enter your name: ";
$name=read();
echo "Enter your age: ";
$age=read();
echo "Hi $name, Isn't it Great to be $age years old?";
@fclose($StdinPointer);
?>

"Do not use the following reserved device names for the name of a file:
CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, 
LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9. Also avoid these names 
followed immediately by an extension; for example, NUL.txt is not recommended. 
For more information, see Namespaces"
it is a windows limitation.
see:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx

download: i need a function to simulate a "wget url" and do not buffer the data in the memory to avoid thouse problems on large files:
<?php
function download($file_source, $file_target) {
        $rh = fopen($file_source, 'rb');
        $wh = fopen($file_target, 'wb');
        if ($rh===false || $wh===false) {
// error reading or opening file
           return true;
        }
        while (!feof($rh)) {
            if (fwrite($wh, fread($rh, 1024)) === FALSE) {
                   // 'Download error: Cannot write to file ('.$file_target.')';
                   return true;
               }
        }
        fclose($rh);
        fclose($wh);
        // No error
        return false;
    }
?>

If you need fopen() on a URL to timeout, you can do like:
<?php
  $timeout = 3;
  $old = ini_set('default_socket_timeout', $timeout);
  $file = fopen('http://example.com', 'r');
  ini_set('default_socket_timeout', $old);
  stream_set_timeout($file, $timeout);
  stream_set_blocking($file, 0);
  //the rest is standard
?>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
<?php
// generiereHostliste.php

function generiereHostliste($file) {

   // aus Rechnerliste.csv lesen
   $fp = fopen($file, "r");
   while($row = fgetcsv($fp, 0, ";")) {       
        $liste[]=[$row[0].";10.16.".$row[1].".".$row[2]]; 
        
   }  
   fclose($fp);

   // in Hostliste.csv schreiben
   $fp = fopen("Hostliste.csv", "w");
   foreach($liste as $row) {
       echo "<pre>";
       print_r($row);
       echo "</pre>";
        fputcsv($fp, $row, ";");
   }
   fclose($fp);
}
// Test
$file = "Rechnerliste.csv";
generiereHostliste($file);

?>
</body>
</html>

Please note that you cannot write to a HTTP resource, for example for doing a PUT request.

You will get this error: 'Failed to open stream: HTTP wrapper does not support writeable connections'

To do a PUT you can only populate the 'content' key of the HTTP context, or use Curl instead.

Opening a file in "r+" mode, and then trying to set the file pointer position with ftruncate before reading the file will result in file data loss, as though you opened the file in "w" mode.

EX:

$File = fopen($FilePath,"r+");  // OPEN FILE IN READ-WRITE

ftruncate($File, 0);  // SET POINTER POSITION (Will Erase Data)

while(! feof($File)) {  // CONTINUE UNTIL END OF FILE IS REACHED

    $Line = fgets($File);  // GET A LINE FROM THE FILE INTO STRING
    $Line = trim($Line);  // TRIM STRING OF NEW LINE
}

ftruncate($File,0); // (Will Not Erase Data)

fclose($File);