Copyright © 2003 Pearson Education, Inc. Slide 6b-1 The Web Wizard’s Guide to PHP by David Lash.

Copyright © 2003 Pearson Education, Inc. Slide 6b-1

The Web Wizard’s Guide to PHPby David Lash


CHAPTER 6Working with Files:

Using files on the Web Server From PHP Scripts

Copyright © 2003 Pearson Education, Inc.

Objectives To learn to work with files to store and retrieve

data To understand the types of applications that can

use File I/O


Why Use Files Files can provide an easy mechanism for storing

data between executions of scripts: store customer data store page hit counts remember end-user preferences store product inventory


Reading A file the easy way. You can use the file() function to read an entire

file into a PHP array Each array item will be assigned 1 line For example:

$inf ='mydata.txt'; $infile = file ($inf); print "$infile[0]";

print "$infile[2]";

Open mydata.txt and read into $infile array.

Output the1st and then 3rd lines of mydata.txt


So if mydata.txt was stored in the same directory as your PHP script and contained:

Apples are red.Bananas are yellow.Carrots are orange.Dates are brown.

Would output:Apples are red.

Carrots are orange. Using file() works well but does consume memory

Can slow scripts down for large files

Reading A file the easy way.


Using fopen() to open files

Use the fopen() script to create a connection to a file once connected can read or write a line at a

time

$file_ptr = fopen ($fileloc, 'r');

The filename of the file on the web server.

A file handle used to refer to the file in your program.

$fileloc = '/home/phppgm/data/data.txt';

File open mode.("r" means read only)


Using file open mods

Table 6.3 File Open Modes for Use with the fopen() Function

Open Mode

Description

r Read-only mode opens the file for reading but not writing.

r+ Read and write mode opens the file for reading and writing.

w Write-only mode opens a file for writing. If the file exists, it overwrites the existing file when writing. If the file doesn’t exist, it creates a new file.

w+ Read and write overwrite mode opens the file for writing and reading. If the file exists, it overwrites the existing file when writing.. If the file doesn’t exist, it creates a new file.

a Append mode opens the file for writing but will append any data written to the end of the existing file. If the file doesn’t exist, this command creates a new file.

a+ Read and append mode opens the file for writing and reading. Any written data is appended to the existing file. If the file doesn’t exist, writing data will create a new file.


Dealing with fopen() failure

The fopen() function can fail for a number of reasons: file location, file permissions, corrupt file

Provide an option for fopen() to output a message if it fails:

$inf = '/home/phppgm/data/mydata.txt'; $FILEH = fopen($inf, 'r') or die ("Cannot open $inf");

Only run die() when fopen()fails.


Using fgets() to read

Once a file is open for reading, use fgets() to read it:

$var = fgets(filehandle, length);

The filehandle of thefile used in the fopen()function.

Optional argument thatindicates one more thanthe maximum numberof bytes to read.

Variable will receive thecharacters read from thefile.


A Full Script Example Consider an example script that invites an end-user to

select a product number: Provides information about the product. Uses the following HTML form input line:

<input type="radio" name="id" value=$item>

Also uses the following input file: AC1000:Hammers:122:12.50AC1001:Wrenches:5:5.00AC1002:Handsaws:10:10.00AC1003:Screwdrivers:222:3.00


PHP Script

Show Source Code

Show data file


The Output ...The previous code can be executed at:

http://itm325.itmbsu.net/jstudent/Examples/Ch6/drive_invent.html


Writing to Files

You can use the fputs() function

The above outputs: “My script was here” into the file that $OFILE points to

The filehandle of the file to writeto.

Returns numberof bytes written or false(0) ifan error.

$message = "My script was here";$ret = fputs($OFILE, $message);

The data to output.


Putting it all together

Consider the following script that: opens a file, writes one line to it closes the file

$inf ='/home/phppgm/data/log.txt'; $FILEH = fopen($inf, 'w') or die("Cannot open $inf"); fputs($FILEH, 'Apples are red');

fclose ($FILEH);


A Full Script Example

Consider another example that appends end-user comments to the end of a file: Asks end-user for comments about site. Uses the following HTML form input line:

<br><textarea rows="1" cols="50" name="comments"></textarea>


PHP Script

Show Source Code

Show Data File

Run Script: http://itm325.itmbsu.net/jstudent/Examples/Ch6/driveappend.html


Locking a File

Web application have potential for many users to execute the same script at same time If scripts attempt to write to the same file at

the same instance in time it may corrupt the file

A corrupted file is a useless unintelligible mixture of data.


Using flock

PHP provides a flock() function that can ensure only one script at a time writes to a file. Use it in your scripts as a defense against file

corruption Use flock($FILEH, LOCK_UN) to unlock a file. Closing

a file ( fclose() ) will also release a lock.

File handle that indicates whatfile to lock.

Returns false (0) ifnot successful.

$ret = flock($FHILE, LOCK_EX);Lock type: LOCK_EX meansonly 1 program can read/writeto file at a time.


Tip: Using the newline character \n

Use the \n character to output a new line character into the file. If you omit the new line character, the appended text will appear together on the same line if you run the script twice, for example:

My script was hereMy script was here

If your script puts an \n at the lines’ end:

My script was here

My script was here


Reading and Writing Files

When reading and writing from the same file you can use the rewind() function to reset the file pointer to start of file:

$ret = rewind(filehandle);


Reading and Writing Files For example consider:

1. $FILEH = fopen('myfile.txt', 'r+');2. $inline = fgets($FILEH, 4096);3. rewind($FILEH);4.$ret= fputs($FILEH, 'Z');

Suppose myfile.txt contains:ABC

After script segment runs, the file will contain: ZBC


A Full Script Example

Consider a script that implements a web page hit counter using the counter file ctr.txt.


A Full Script Example: Accessing the counter

The script could be placed in a file named counter.php and accessed through an include statement as:

<?php include 'counter.php' ?>

For example: <html><head><title>Harry's Place </title></head><body><font size=5 color=blue>Happy Harry's Hardware Home</font>

<br><?php include 'counter.php' ?>

</body></html>


PHP Script

Show Source Code

Show counter file

Show code to be used with include function



http://itm325.itmbsu.net/jstudent/Examples/Ch6/drivecounter.php


Another Full Script Example

Consider another example that implements an on-line survey: Asks end-user to select favorite tool

<input type="radio" name="tool" value="hammer" checked> Hammer<input type="radio" name="tool" value="wrench"> Wrench<input type="radio" name="tool" value="sdriver"> Screwdriver

<input type="radio" name="tool" value="fryingpan"> Frying Pan

Use survey file /home/phppgm/data/survey1.txt. 0:0:0:0 initial value


PHP Script

Show Source Code

Show Data File



http://itm325.itmbsu.net/jstudent/Examples/Ch6/drivesurvey.html


Summary

Working with files enable scripts to store data for long periods of time. file() - read file into an array fopen() - open a file fgets() - read a line from file fputs() - write to a file. flock() - lock access to file.

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Copyright © 2003 Pearson Education, Inc. Slide 6b-1 The Web Wizard’s Guide to PHP by David Lash.

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