Intro to PHP

Dr. Andrew Besmer

About PHP

The Language

PHP
PHP Hypertext Preprocessor
  • Recursive acronym
  • Open source
  • Available on most OS
  • Portable code

Similarities

  • Code similar to
    • C
    • Java
    • Perl
  • Take some concepts with you or reuse existing
  • Used primarily to write dynamic server side web apps
    • Can be used to make cli scripts

Running PHP

  • You can run PHP several ways:
    • Through a web server like Apache
    http://localhost/myFile.php
    • Directly from the command line
    php myFile.php

Interpreted Language

PHP is an interpreted language

  • Pros
    • Program can change dynamically at runtime
    • Easier to program with, just code and run!
    • Easier to move from one OS/Architecture to another
  • Cons
    • Without compiling syntax errors may go undetected
    • Can be problematic for performance
      • Can be mitigated via caching

Basic Syntax

PHP mode

  • Can move in and out of “PHP mode” as you need
    • Move into using the start tag <?php
    • Can exit by using the end tag ?>
    <?php
  //PHP mode
?>
  • Execution depends on code location
    • Inside is code to be run on the server
    • Outside is ignored by interpreter and outputted1
  • It is good practice to leave off the closing tag in a PHP only file

PHP mode

  • PHP is most frequently combined with HTML/CSS/JS for making web apps
<!DOCTYPE html>
<html>
    <head>
        <title>First App</title>
    </head>
    <body>
        <?php echo "Hi CSCI Students!"; ?>
    </body>
</html>
  • Can be used to do many other things
    • Generate PNG/JPG
    • Generate JSON/XML
    • Generate PDF

Statements

Statement
Instruction given within the language.
  • When in PHP mode the interpreter will evaluate and execute each statement then move to the next
  • Each statement must end with a semicolon ;2

Comments

  • Single line comments use //
<?php
// This is a single line comment
echo "This line is run!";
  • Multi line comments use /* to start them and */ to end them
<?php
/*
 This is a multi line comment
 echo "These statements were commented out.";
 echo "So they will not be executed or output";
*/
  • A # can also be used but seldom is
<?php
# I'm not used often

Comments

Warning

  • Do not nest the multi line comments they end at the first */
<?php
/*
    echo 'This will not end well!'; /* Do you see the problem? */
*/

Variables

Variables

Variable
Named reference to a storage location in main memory (RAM) who’s value can change.
  • Which would you rather?
0x00BAB10C
$uberBlock

Variables

  • Variable names should start with a $
  • Variable names
    • Are case sensitive
    • Must start with letter or _ followed by letters, numbers, or underscores
    • Variable names should be $camelCasedForReadability
    • $this is a reserved variable (more later)

  1. Exception is using conditionals for output, more on this later.↩

  2. Exception is when closing the PHP tag. Don’t do this!↩