PHP File Handling

Jussi Pohjolainen

Tampere Polytechnic University of Applied Sciences » ICT

Web architecture

• Three-tiered web app contains a place for persistent storage
• Persistent storage can be a file (text, xml, binary) or a database
• File-handling doesn't require other technologies (like database)
• File-handling is not a very good strategy for three-tiered web app.. lacks all the good qualities that comes prebuilt in databases (locking, transactions, user restrictions etc.)

Three tiered architecture

PHP and File Handling

• PHP includes a lot of built-in functions for file handling
• It's possible to read, write, delete and get information about files using these functions.
• Note: you have to make sure that your files have right permissions. (SSH terminal: chmod)

Opening a file or directory

• Opening a file: fopen($filename, $mode)
• Different modes for opening a file: for reading (r), writing (w). etc.
• fopen returns a handle that is used for reading and writing.
• Closing file stream fclose($handle)
• Opening directory: opendir($dirname)
• Closing directory: closedir($dirname)

Creating file

• Creating file using fopen (no error handling in this example):

  $file = "/dir/file.txt";
  $newfile = fopen($file, "w+");
  fclose($newfile);
  

• See all the modes from php-documentation.

Reading file using fgets

• fgets-function reads one line at a time.
• Example: (no error handling in this example)

  $file = "file.txt";
  $handle = fopen($file, "r");
  print fgets($handle);
  fclose($handle);
  

• Using loop:

  $handle = fopen("/tmp/inputfile.txt", "r");
  while (!feof($handle)) {
         $buffer = fgets($handle);
         print $buffer;
  }
  fclose($handle);
  

Writing to a file using fputs

• Example

  $handle = fopen("file.txt", "a");
  fputs($handle, "line\n");
  fclose($handle);
  

Locking

• What happens if several users try to save a file at the same time?
• => File corrupts
• flock() functions locks a file
• flock() takes to parameters: file handle and operation. Operation is one of the following:
  • LOCK_SX: shared lock (reader)
  • LOCK_EX: exclusive lock (writer)
  • LOCK_UN: release lock (either shared or exclusive)

Example of file Locking

• $fp = fopen("/tmp/lock.txt", "w+");
  flock($fp, LOCK_EX)
  fputs($fp, "Write something here\n");
  flock($fp, LOCK_UN);
  fclose($fp);
  

Error handling

• When handling files, many things can go wrong..

• if(!($fp = fopen("/tmp/lock.txt", "w+"))) {
      print "Cannot open file.";
  }
  if(!(flock($fp, LOCK_EX))) {
      print "Cannot lock the file";
  }
  if(!(fputs($fp, "Write something here\n"))) {
      print "Cannot write to a file";
  }
  if(!(flock($fp, LOCK_UN))) {
      print "Cannot unlock the file";
  }
  if(!(fclose($fp))) {
      print "Cannot close the handle";
  }
  

Create your own functions with error handling

• function file_put_contents($file, $data) {
      if(!($fp = fopen($file, "w+"))) {
          return false;
      }
      .
      .
      return true;
  }
  
  file_put_contents("file.txt", "Hello!");
          
  

• .. but infact this method already exists: http://fi.php.net/file_put_contents

file_put_contents

• The file_put_contents(file,data,mode,context) writes a string to a file.
• This function follows these rules when accessing a file:
  • Create the file if it does not exist
  • Open the file
  • Lock the file if LOCK_EX is set
  • If FILE_APPEND is set, move to the end of the file. Otherwise, clear the file content
  • Write the data into the file
  • Close the file and release any locks
• Usage: file_put_contents("file.txt", "Hello!", LOCK_EX);

Copying and deleting files

• copy()
• rename()
• unlink()