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Chapter 6: Files and Directories

6.1 Opening files, Writing to a file

[ After running this program, test.txt file will becreated and data will be written onto it.]

6.2 Locking a file, Reading a file content

The flock() function locks or releases a file.

This function returns TRUE on success or FALSE on failure.

Syntax: flock(file,lock,block)

Parameter Description

file Required. Specifies an open file to lock or release

lock Required. Specifies what kind of lock to use.Possible values:

LOCK_SH - Shared lock (reader). Allow other processes to accessthe file

LOCK_EX - Exclusive lock (writer). Prevent other processes fromaccessing the file

LOCK_UN - Release a shared or exclusive lock

LOCK_NB - Avoids blocking other processes while locking

block Optional. Set to 1 to block other processes while locking

Note: These locks only apply to the current PHP process. Other processes can modify or delete a PHP-

locked file if permissions allow.

Note: flock() is mandatory under Windows.

Tip: The lock is released also by fclose(), which is called automatically when script is finished.

successfully written to test.txtNot able to readWrite something

[When a file is exclusively locked, otherprocesses cannot read or write that fileuntil it is unlocked.]

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6.3 Handling file upload

A PHP script can be used with a HTML form to allow users to upload files to the server. Initially files are

uploaded into a temporary directory and then relocated to a target destination by a PHP script.

Information in the phpinfo.phppage describes the temporary directory that is used for file uploads

as upload_tmp_dirand the maximum permitted size of files that can be uploaded is stated

as upload_max_filesize. These parameters are set into PHP configuration file php.ini.

An uploaded file could be a text file or image file or any document.Creating an upload form:The following HTM code below creates an uploader form. This form is having method attribute setto postand enctype attribute is set to multipart/form-dataCreating an upload script:There is one global PHP variable called $_FILES. This variable is an associate double dimension arrayand keeps all the information related to uploaded file. So if the value assigned to the input's name attributein uploading form was file, then PHP would create following five variables:

$_FILES['file']['tmp_name']-the uploaded file in the temporary directory on the web server.

$_FILES['file']['name'] -the actual name of the uploaded file.

$_FILES['file']['size'] -the size in bytes of the uploaded file. $_FILES['file']['type'] -the MIME type of the uploaded file.

$_FILES['file']['error'] -the error code associated with this file upload.

Uploadform.htm

Photo:

Upload.php

Note: Create a folder by name upload in www folder and then run uploadform.htm from local host.Then, what ever file you upload (size must be less than 2mb-see php.ini file MAX_UPLOAD_SIZE is2mb only) that will be uploaded to upload folder that you created .

6.4 Working with directories

Creating Directories in PHP

A new directory can be created in PHP using the mkdir() function.

Deleting a Directory

Directories are deleted in PHP using the rmdir() function. rmdir() takes a single argument, the name of the

directory to be deleted. The deletion will only be successful if the directory is empty. If the directory

contains files or other sub-directories the deletion cannot be performed until those files and sub-

directories are also deleted.

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Finding and Changing the Current Working Directory

It is unlikely that a web application will be able to perform all of its file related tasks in a single directory.

For this reason, it is vital to be able to both find out the current working directory, and change to another

directory from within a PHP script.The current working directory can be identified using the getCwd() function:

The current working directory can be changed using the chdir() function. chdir() takes as the only

argument the path of the new directory:

Listing Files in a Directory

The files in a directory can be read using the PHP scandir() function. scandir() takes two arguments. The

first argument is the path the directory to be scanned. The second optional argument specifies how the

directory listing is to be sorted. If the argument is 1 the listing is sorted reverse-alphabetically. If the

argument is omitted or set to 0 the list is sorted alphabetically:

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