PHP script does nothing. How to debug?

Put below line on the top of the your script.

ini_set('display_errors', 'On');
error_reporting(E_ALL);

Which will show you if there is any error in the script.

Check your php.ini settings.

Inside your php.ini:

display_errors = On
error_reporting = E_ALL

then restart your web server and try again.

Being a programmer, knowing to use a debugging tool is a handy. I suggest you to use xdebug

As a last resort, ( as others mentioned the preferred ways )

You can comment all the code out, and back track the code tell it stops, just be mindful of if{ } blocks and other control structures. For example.. say you have this code.

<?php

function do_nothing(){

}

$somthing = 1;
if($something){
  do_nothing();
}

$badCode = 'hello'

$array = array(1,2,3,4,5);

foreach($array as $item ){
   echo 'item: '.$item;
}

outputs nothing, because it's broken.

You could

<?php
/*
function do_nothing(){

}

$somthing = 1;
if($something){
  do_nothing();
}

$badCode = 'hello'

$array = array(1,2,3,4,5);

foreach($array as $item ){
   echo 'item: '.$item;
}
*/
echo 'works';

outputs

'works'

And continue to

<?php
/*
function do_nothing(){

}

$somthing = 1;
if($something){
  do_nothing();
}

$badCode = 'hello'
*/
$array = array(1,2,3,4,5); //need this for the loop
foreach($array as $item ){
 //don't comment half this block
   echo 'item: '.$item;
}

echo 'works';

Outputs

'item: 1'

'item: 2'

'item: 3'

'item: 4'

'item: 5'

'works'

And finally

<?php
/*
function do_nothing(){

}

$somthing = 1;
if($something){
  do_nothing();
}
*/
$badCode = 'hello'

$array = array(1,2,3,4,5); //need this for the loop
foreach($array as $item ){
 //don't comment half this block
   echo 'item: '.$item;
}

echo 'works';

Broken, ( missing semicolon $badCode = 'hello'; )

It's a rudimentary way to debug, to be sure. but it will work 100% of the time if you respect the control blocks..

Also be sure to be familiar with the different print functions.

• echo — Output one or more strings
• print_r — Prints human-readable information about a variable
• var_export — Outputs or returns a parsable string representation of a variable
• var_dump — Dumps information about a variable
• debug_backtrace — Generates a backtrace

I'm sure there are more of these but those are the most common. Its also useful to use a <pre> tag before printing objects and array to preserve the whitespace and make them easy to read.

I also like to use this little function ( which can tell you what line you printed from )

/**
 * export a variable with line number from backtrace using offset
 * @param mixed $var
 * @param int $offset
 */
function print_debug($var=null, $offset=0){
    $stacktrace = debug_backtrace(false);
    $trace = $stacktrace[$offset];
    extract($trace);
    echo "<span style='color: #CCC;'> Output from FILE[ $file ] LINE[ $line ]</span>";
    echo "<pre>";
    var_export($var);
    echo "</pre>";
}