Debugging PHP

Useful links

Debugging in PHP
About debugging in PHP
A Detailed Guide to PHP Debugging
howto debug PHP code

Warning: PHP does a syntax check before executing the code. If the syntax check fails the program can terminate without any (error)message

^M

The program looks like

#! /usr/bin/php
<?php
The code
?>

When you run it you get an error:

/usr/bin/php^M: bad interpreter: No such file or directory

This can be solved by opening the program in a text editor like Geany and then

CTRL-A
CTRL-C
CTRL-N
CTRL-V
CTRL-S and save the file under the same or a new name

Try again

Build in functions

Sometimes if you expect that a function is already build in into PHP, or that a function which is build in into PHP, can solve your issue. This in not always the case. You will need to write your own function / code in those cases to solve the issue.

Some functions

Functions to use for debugging when the script is ran from a webbrowser

Function	Explanation
echo	Output one or more strings
nl2br	Inserts HTML line breaks before all newlines in a string
echo nl2br (“\nThis text will be printed\n”);	Prints some text. Use a new line at the beginning and at the end of the text to make sure the text is on a separate line
print_r ($somevariable);	Prints human-readable information about a variable
var_dump ($somevariable);	Dumps information about a variable
$resultvariable = is_bool ($somevariable); var_dump($resultvariable);	Check if a variable is a boolean
$resultvariable = is_bool ($somevariable); echo nl2br ($resultvariable ? 'true' : 'false');	Check if a variable is a boolean
$resultvariable = is_int( $somevariable[0]); var_dump($resultvariable);	Check if element 0 of array somevariable is an integer
echo nl2br (“Showing if somevariable is an array: ” . is_array($somevariable) . “ 1: it is an array, 0: no array\n”);	Check if a variable is an array
echo nl2br (“Showing characterset: ” . mb_internal_encoding() . “\n”);	Get the internal character encoding

Tools

Database management

With phpMyAdmin a mySQL database can be managed
Adminer is a replacement for phpMyAdmin in a single PHP file

Debugging

Firebug is deprecated. This is what followed Firebug

Install Xdebug

Do, logged in as root, in a termiknal

Install with aptitude php-dev or for your specific version, an example: php7.0-dev
pecl channel-update pecl.php.net
mount -o remount,exec /tmp/ or whereever the temporary directory is located pecl uses
- If needed do mount -o remount,noexec /tmp/ to restore /tmp/ to its original state
pecl install xdebug

Then you should get a lot of output from the compiler (make) which ends with something like

----------------------------------------------------------------------
Libraries have been installed in:
   /tmp/pear/temp/pear-build-rootiu8Wto/xdebug-2.9.0/modules

If you ever happen to want to link against installed libraries
in a given directory, LIBDIR, you must either use libtool, and
specify the full pathname of the library, or use the '-LLIBDIR'
flag during linking and do at least one of the following:
   - add LIBDIR to the 'LD_LIBRARY_PATH' environment variable
     during execution
   - add LIBDIR to the 'LD_RUN_PATH' environment variable
     during linking
   - use the '-Wl,-rpath -Wl,LIBDIR' linker flag
   - have your system administrator add LIBDIR to '/etc/ld.so.conf'

See any operating system documentation about shared libraries for
more information, such as the ld(1) and ld.so(8) manual pages.
----------------------------------------------------------------------

Build complete.
Don't forget to run 'make test'.

running: make INSTALL_ROOT="/tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0" install
Installing shared extensions:     /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0/usr/lib/php/20151012/

  +----------------------------------------------------------------------+
  |                                                                      |
  |   INSTALLATION INSTRUCTIONS                                          |
  |   =========================                                          |
  |                                                                      |
  |   See https://xdebug.org/install.php#configure-php for instructions  |
  |   on how to enable Xdebug for PHP.                                   |
  |                                                                      |
  |   Documentation is available online as well:                         |
  |   - A list of all settings:  https://xdebug.org/docs-settings.php    |
  |   - A list of all functions: https://xdebug.org/docs-functions.php   |
  |   - Profiling instructions:  https://xdebug.org/docs-profiling2.php  |
  |   - Remote debugging:        https://xdebug.org/docs-debugger.php    |
  |                                                                      |
  |                                                                      |
  |   NOTE: Please disregard the message                                 |
  |       You should add "extension=xdebug.so" to php.ini                |
  |   that is emitted by the PECL installer. This does not work for      |
  |   Xdebug.                                                            |
  |                                                                      |
  +----------------------------------------------------------------------+


running: find "/tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0" | xargs ls -dils
137518    0 drwxr-xr-x 3 root root      60 dec 14 19:16 /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0
139134    0 drwxr-xr-x 3 root root      60 dec 14 19:16 /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0/usr
139135    0 drwxr-xr-x 3 root root      60 dec 14 19:16 /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0/usr/lib
139475    0 drwxr-xr-x 3 root root      60 dec 14 19:16 /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0/usr/lib/php
137962    0 drwxr-xr-x 2 root root      60 dec 14 19:16 /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0/usr/lib/php/20151012
137966 1796 -rwxr-xr-x 1 root root 1835992 dec 14 19:16 /tmp/pear/temp/pear-build-rootiu8Wto/install-xdebug-2.9.0/usr/lib/php/20151012/xdebug.so

Build process completed successfully
Installing '/usr/lib/php/20151012/xdebug.so'
Segmentation fault

Something about the Segmentation fault warning
Run make test
- This results in: “make: *** No rule to make target 'test'. Stop.” Are we missing something?
Goto Configure PHP and follow the instructions
- vi /etc/php/7.0/apache2/php.ini
- Add to the end: zend_extension=“/usr/lib/php/20151012/xdebug.so” or where ever xdebug.so is located.
  - You can use find / -type f -name xdebug.so 2> /dev/null to find it
  - and also for vi /etc/php/7.0/cli/php.ini
  - The end of php.ini should look like

; Added for Xdebug
zend_extension="/usr/lib/php/20151012/xdebug.so"
; End:

Restart the webserver.
- In case of Apache do: systemctl restart apache2 and / or systemctl restart apache2.service
- In case of Lighttpd do: systemctl restart lighttpd and / or systemctl restart lighttpd.service
Run php -m and look for

 [Zend Modules]
 Xdebug
 Zend OPcache

Run /var/www/html/test.php or where ever the contents of your webserver is stored. This should be in test.php
Do chmod 644 /var/www/html/test.php

<!DOCTYPE HTML>
<html>
  <head>
    <title>PHP Test</title>
  </head>
  <body>
    <?php echo '<p>Hello World</p>'; ?>
    Hello, Here is "some" info about PHP on this computer
    <?php
      phpinfo();
      $d = date("D");
      if($d == "Fri" || $d == "Sat"){
        echo "Have a nice weekend!";
      }
      else {
	echo "It is not a weekend tomorrow. Have a nice day with a lot of fun!!!";
      }
    ?>
  </body>
</html>

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