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-2 CHAPTER 6 Working 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

Copyright © 2003 Pearson Education, Inc. Slide 6b-4 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

Copyright © 2003 Pearson Education, Inc. Slide 6b-5 Reading A file the easy way. You can use the file() function to read an entire file into a PHP arrayfile() 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

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

Copyright © 2003 Pearson Education, Inc. Slide 6b-7 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

Copyright © 2003 Pearson Education, Inc. Slide 6b-8 Using file open modsfile open mods

Copyright © 2003 Pearson Education, Inc. Slide 6b-9 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.

Copyright © 2003 Pearson Education, Inc. Slide 6b-10 Using fgets() to read Once a file is open for reading, use fgets() to read it:fgets()

Copyright © 2003 Pearson Education, Inc. Slide 6b-11 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: Also uses the following input file: AC1000:Hammers:122:12.50 AC1001:Wrenches:5:5.00 AC1002:Handsaws:10:10.00 AC1003:Screwdrivers:222:3.00

Copyright © 2003 Pearson Education, Inc. Slide 6b-12 PHP Script Show Source Code Show data file

Copyright © 2003 Pearson Education, Inc. Slide 6b-13 The Output... The previous code can be executed at:

Copyright © 2003 Pearson Education, Inc. Slide 6b-14 Writing to Files You can use the fputs() function The above outputs: “ My script was here” into the file that $OFILE points to

Copyright © 2003 Pearson Education, Inc. Slide 6b-15 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);

Copyright © 2003 Pearson Education, Inc. Slide 6b-16 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:

Copyright © 2003 Pearson Education, Inc. Slide 6b-17 PHP Script Show Source Code Show Data File Run Script:

Copyright © 2003 Pearson Education, Inc. Slide 6b-18 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.

Copyright © 2003 Pearson Education, Inc. Slide 6b-19 Using flock PHP provides a flock() function that can ensure only one script at a time writes to a file.flock() 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.

Copyright © 2003 Pearson Education, Inc. Slide 6b-20 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

Copyright © 2003 Pearson Education, Inc. Slide 6b-21 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);

Copyright © 2003 Pearson Education, Inc. Slide 6b-22 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: A B C After script segment runs, the file will contain: Z B C

Copyright © 2003 Pearson Education, Inc. Slide 6b-23 A Full Script Example Consider a script that implements a web page hit counter using the counter file ctr.txt.

Copyright © 2003 Pearson Education, Inc. Slide 6b-24 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: For example: Harry's Place Happy Harry's Hardware Home

Copyright © 2003 Pearson Education, Inc. Slide 6b-25 PHP Script Show Source Code Show counter file Show code to be used with include function

Copyright © 2003 Pearson Education, Inc. Slide 6b-26 The Output... The previous code can be executed at:

Copyright © 2003 Pearson Education, Inc. Slide 6b-27 Another Full Script Example Consider another example that implements an on-line survey: Asks end-user to select favorite tool Hammer Wrench Screwdriver Frying Pan Use survey file /home/phppgm/data/survey1.txt. 0:0:0:0 initial value

Copyright © 2003 Pearson Education, Inc. Slide 6b-28 PHP Script Show Source Code Show Data File

Copyright © 2003 Pearson Education, Inc. Slide 6b-29 The Output... The previous code can be executed at:

Copyright © 2003 Pearson Education, Inc. Slide 6b-30 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.