En/php debug - Revision history

Wikiuser at 13:58, 21 March 2022

2022-03-21T13:58:13Z

Wikiuser: Links update, template adoption and SEO tag inclusion

2016-02-09T22:55:34Z

Links update, template adoption and SEO tag inclusion

Wikiuser: Links update and some minor fixes. Moreover the new syntax highlight extension was enabled

2015-12-23T22:10:02Z

Links update and some minor fixes. Moreover the new syntax highlight extension was enabled

Wikiuser: Corrected Operative System in Operating System

2015-02-14T22:30:20Z

Corrected Operative System in Operating System

Wikiuser at 21:30, 29 December 2014

2014-12-29T21:30:28Z

Wikiuser: Added page about debugging techniques in PHP

2014-12-29T21:21:34Z

Added page about debugging techniques in PHP

New page

Welcome to Simone Giustetti's wiki pages.

Languages: '''English''' - [http://www.giustetti.net/wiki/index.php?title=php_debug Italiano]

----

== Introduction ==

Every software developer spends a certain amount of her/his working time '''searching and correcting errors'''; an activity commonly referred to as '''debug'''. There is no denying it: as long as we will have programs errors will exist and we will need fixes and workarounds for them. Every modern programming language comes with tools, both embedded or external, some more powerful than others, meant to help in '''fixing bugs'''. In this specific aspect '''PHP''', a language widely used in developing dynamic web sites, is somewhat lacking when compared to similar tools. A gap that should be filled with release 5.6 and the introduction of an '''internal debugger''', a tool to allow developers to follow the source code flow while in execution. The following paper will instead describe some tools to debug PHP source code written with older releases of the language. Tools complementing the internal debugger that prove to be invaluable to developers when maintaining production code.

== PHP language ==

PHP is a general purpose programming language aimed for fast script development, well suited for producing '''dynamic web pages'''. In this specific configuration PHP is executed on '''a remote server''' where it generates HTML pages then sent to a web browser. Users requesting web pages will receive them without any sign of server executed PHP code.

While fast web site development is PHP main goal, the language can be used to write scripts that don't need any server and are able to run on a local host from the command line. Such scripts are ideal for repetitive tasks, even complex ones, and can be scheduled through the operative system provided scheduling services. Local scripts do not require any web server, browser, database or other service but only need the PHP language parser.

== PHP development ==

Whatever the reason to use PHP, writing code proves to be a fairly simple task and requires neither specific tools nor development environments, but only:
# The '''language parser'''.
# A '''text editor''' of choice.
Once the two listed prerequisites are installed you can start writing PHP code. To execute the completed script open a terminal emulator and run command:
'''php''' ''-f'' <script>
where <script> is the text file containing the lines of code. Execute the command in the directory where your scripts are located. Feedback messages, warnings and error messages produced by the code will be output to video during execution.

== PHP and syntax analysis ==

PHP bare installation provides some tools useful when searching trough the source code for errors. Executing a '''syntax analysis''' of PHP code is a fairly straightforward task provided local access to the scripts is granted. To check the syntax of script hello_world.php placed inside directory /home/sviluppo/php/ open a '''shell''' or a '''similar terminal emulator''' an move to the directory:
'''cd''' /home/sviluppo/php/
then run the php parser using option ''-l'' that forces a syntax check of the file:
'''php''' ''-l'' ./hello_world.php
The parser will return
bash-4.2$ '''php''' ''-l'' hello_world.php
'''No syntax errors detected''' in hello_world.php
when no syntax error is found. Otherwise an error message related to the first issue encountered while parsing the code will be output to screen:
bash-4.2$ '''php''' ''-l'' hello_world.php
'''PHP Parse error: syntax error''', unexpected 'echo' (T_ECHO), expecting ',' or ';' in hello_world.php '''on line 3'''
'''Errors parsing''' hello_world.php
All of the error messages will show:
* An '''error description'''.
* The '''parsed line of code'''.
When an issue is resolved, run the command again and parsing will stop when the next error is found:
bash-4.2$ '''php''' ''-l'' hello_world.php
'''PHP Parse error: syntax error''', unexpected '' <title>PHP Test</title' (T_CONSTANT_ENCAPSED_STRING) in hello_world.php '''on line 4'''
'''Errors parsing''' hello_world.php
The procedure can be recursively repeated for each error found by the parser at every consecutive run. Once all issues are resolved, message "No syntax errors detected" will be output giving proof of source code syntax correctness.

Below are three PHP listings referring to the parser runs executed in the above lines. Some syntax errors, even really dumb ones, were added to the first two. The main difference among the two being the resolution of the bug at line 2 where an ";" character was added to close the line of code. The third and last listing contains the correct code.

''hello_world.php - Listing 1'': Contains many syntax errors.
<?php
echo '<html>'
echo ' <head>';
iechio ' <title>PHP Test</title>';
echo ' </head>";
echo' <body>';
echo ' <nowiki><p>Hello World</p></nowiki>'; ?>
echo '</body>";
echo '</html>';
?>
''hello_world.php - Listing 2'': The first parser signaled bug was resolved.
<?php
echo '<html>';
echo ' <head>';
iechio ' <title>PHP Test</title>';
echo ' </head>";
echo' <body>';
echo ' <nowiki><p>Hello World</p></nowiki>'; ?>
echo '</body>";
echo '</html>';
?>
''hello_world.php - Listing 3'': Correct syntax.
<?php
echo "<html>\n";
echo " <head>\n";
echo " <title>PHP Test</title>\n";
echo " </head>\n";
echo " <body>\n";
echo " <nowiki><p>Hello World</p></nowiki>'; ?>
echo " </body>\n";
echo "</html>\n";
?>

== PHP and variable content ==

Syntax analysis proves to be an useful tool for error spotting, but it mainly highlights mistypings and missing characters while typing code. Syntax errors are fairly easy to spot and correct. '''Logic errors''' are usually more difficult to find and resolve. Logic errors only show up while the code is in execution. To understand such errors requires to follow the code flow through the parsed files, understand their order of execution and print out a list of variables and their respective content. PHP offers a relatively scarce number of tools to perform such task: '''backtrace and dump''' functions.

Backtrace functions return a '''list of source code files parsed during execution and the respective calling functions'''. Two backtrace functions exist:
* '''debug_backtrace()'''.
* '''debug_print_backtrace()'''.

The former returns an associative array whose each component consists of:
* The file containing the call.
* The line of code responsible for calling another file or function.
* The called file / function.
* An array containing the list of parameters passed to the function ant their respective values.
Calls are listed in decreasing order with '''the last one at the top of the list'''. Reading the list top down through each previous call you'll reach the main script.

debug_print_backtrace only returns a list of function calls or file inclusions in decreasing order. Each line shows the called function or included file name, the file containing the call and the corresponding line number. The first line returned by debug_print_backtrace corresponds to the last executed call; searching forwards through the list it is possible to rebuild the source code flow.

The PHP provided dump functions return the list of variables available when calling the function and their respective values. Some dump functions are available:
* '''get_defined_vars()'''.
* '''print_r()'''.
* '''var_export()'''.
* '''var_dump()'''.

Function get_defined_vars returns a list of '''all''' defined variables available when calling it. The list is exported in the form of a multi-dimensional array whose every component is a variable. The remaining functions take a parameter corresponding to the '''searched for variable''' and return its name and value in slightly different formats.

== Conclusions ==

A drawback in using the previously listed functions consists of the '''need to modify the source code'''. A common function driven debug session usually resolves in:
# Deciding which file to begin the analysis with.
# Writing some backtrace or dump functions in it accordingly to ones need.
# Executing code to obtain the desired information.
# Updating more source code files.
# Repeating the above tasks until a bug is found and resolved.
# Removing all the added lines of code to restore the program flow.
The procedure can result difficult and requires a lot of effort and time. It surely would be better to '''follow parser executed code flow without the need to update it'''. This proves to be impossible without installing and configuring some additional tools. Many of such freely available tools are based on [[En/xdebug]], a software that will be thee subject of a future article dealing with its many features, installation and configuration procedures and bindings with some external developers tools.

For any feedback, questions, errors and such, please e-mail me at ''studiosg [at] giustetti [dot] net''

External links

----

* [http://www.php.net PHP language home page]
* [http://php.net/manual/it/ PHP language manual]

----

Languages: '''English''' - [http://www.giustetti.net/wiki/index.php?title=php_debug Italiano]

@@ Line 1: / Line 1: @@
-Welcome to Simone Giustetti's wiki pages.
+{{header_en|title=Debugging PHP scripts| keyword={{Template:keyword_en_php}}| description=Some tips and tricks to debug PHP source code | link_page=php_debug}}
 == Introduction ==
@@ Line 52: / Line 46: @@
 Below are three PHP listings referring to the parser runs executed in the above lines. Some syntax errors, even really dumb ones, were added to the first two. The main difference among the two being the resolution of the bug at line 2 where an ";" character was added to close the line of code. The third and last listing contains the correct code.
 ''hello_world.php - Listing 1'': Contains many syntax errors.
@@ Line 144: / Line 139: @@
 ----
-Languages: '''English''' - [[php_debug | Italiano]]
+{{footer_en | link_page=php_debug}}

← Older revision		Revision as of 22:30, 14 February 2015
Line 16:		Line 16:
	PHP is a general purpose programming language aimed for fast script development, well suited for producing '''dynamic web pages'''. In this specific configuration PHP is executed on '''a remote server''' where it generates HTML pages then sent to a web browser. Users requesting web pages will receive them without any sign of server executed PHP code.		PHP is a general purpose programming language aimed for fast script development, well suited for producing '''dynamic web pages'''. In this specific configuration PHP is executed on '''a remote server''' where it generates HTML pages then sent to a web browser. Users requesting web pages will receive them without any sign of server executed PHP code.

−	While fast web site development is PHP main goal, the language can be used to write scripts that don't need any server and are able to run on a local host from the command line. Such scripts are ideal for repetitive tasks, even complex ones, and can be scheduled through the ~~operative~~ system provided scheduling services. Local scripts do not require any web server, browser, database or other service but only need the PHP language parser.	+	While fast web site development is PHP main goal, the language can be used to write scripts that don't need any server and are able to run on a local host from the command line. Such scripts are ideal for repetitive tasks, even complex ones, and can be scheduled through the operating system provided scheduling services. Local scripts do not require any web server, browser, database or other service but only need the PHP language parser.

← Older revision	Revision as of 13:58, 21 March 2022
(No difference)

@@ Line 2: / Line 2: @@
-Languages: '''English''' - [http://www.giustetti.net/wiki/index.php?title=php_debug Italiano]
+Languages: '''English''' - [[php_debug | Italiano]]
 ----
@@ Line 12: / Line 12: @@
-== PHP language ==
+== PHP Language ==
 PHP is a general purpose programming language aimed for fast script development, well suited for producing '''dynamic web pages'''. In this specific configuration PHP is executed on '''a remote server''' where it generates HTML pages then sent to a web browser. Users requesting web pages will receive them without any sign of server executed PHP code.
@@ Line 19: / Line 19: @@
-== PHP development ==
+== PHP Development ==
 Whatever the reason to use PHP, writing code proves to be a fairly simple task and requires neither specific tools nor development environments, but only:
@@ Line 29: / Line 29: @@
-== PHP and syntax analysis ==
+== PHP and Syntax Analysis ==
 PHP bare installation provides some tools useful when searching trough the source code for errors. Executing a '''syntax analysis''' of PHP code is a fairly straightforward task provided local access to the scripts is granted. To check the syntax of script hello_world.php placed inside directory /home/sviluppo/php/ open a '''shell''' or a '''similar terminal emulator''' an move to the directory:
@@ Line 54: / Line 54: @@
 ''hello_world.php - Listing 1'': Contains many syntax errors.
     <?php
        echo '<html>'
@@ Line 60: / Line 61: @@
        echo '   </head>";
        echo'   <body>';
-       echo '     <nowiki><p>Hello World</p></nowiki>'; ?>
+       echo '     <p>Hello World</p>'; ?>
        echo '</body>";
        echo '</html>';
     ?>
 ''hello_world.php - Listing 2'': The first parser signaled bug was resolved.
     <?php
        echo '<html>';
@@ Line 71: / Line 74: @@
        echo '   </head>";
        echo'   <body>';
-       echo '     <nowiki><p>Hello World</p></nowiki>'; ?>
+       echo '     <p>Hello World</p>'; ?>
        echo '</body>";
        echo '</html>';
     ?>
 ''hello_world.php - Listing 3'': Correct syntax.
     <?php
        echo "<html>\n";
@@ Line 82: / Line 87: @@
        echo "   </head>\n";
        echo "   <body>\n";
-       echo "      <nowiki><p>Hello World</p></nowiki>'; ?>
+       echo "      <p>Hello World</p>\n";
        echo "   </body>\n";
        echo "</html>\n";
     ?>
-== PHP and variable content ==
+== PHP and Variable Content ==
 Syntax analysis proves to be an useful tool for error spotting, but it mainly highlights mistypings and missing characters while typing code. Syntax errors are fairly easy to spot and correct. '''Logic errors''' are usually more difficult to find and resolve. Logic errors only show up while the code is in execution. To understand such errors requires to follow the code flow through the parsed files, understand their order of execution and print out a list of variables and their respective content. PHP offers a relatively scarce number of tools to perform such task: '''backtrace and dump''' functions.
@@ Line 123: / Line 129: @@
 # Repeating the above tasks until a bug is found and resolved.
 # Removing all the added lines of code to restore the program flow.
-The procedure can result difficult and requires a lot of effort and time. It surely would be better to '''follow parser executed code flow without the need to update it'''. This proves to be impossible without installing and configuring some additional tools. Many of such freely available tools are based on xdebug, a software that will be thee subject of a future article dealing with its many features, installation and configuration procedures and bindings with some external developers tools.
+The procedure can result difficult and requires a lot of effort and time. It surely would be better to '''follow parser executed code flow without the need to update it'''. This proves to be impossible without installing and configuring some additional tools. Many of such freely available tools are based on [[En/xdebug|xdebug]], a software that will be thee subject of a future article dealing with its many features, installation and configuration procedures and bindings with some external developers tools.
@@ Line 138: / Line 144: @@
 ----
-Languages: '''English''' - [http://www.giustetti.net/wiki/index.php?title=php_debug Italiano]
+Languages: '''English''' - [[php_debug | Italiano]]

@@ Line 123: / Line 123: @@
 # Repeating the above tasks until a bug is found and resolved.
 # Removing all the added lines of code to restore the program flow.
-The procedure can result difficult and requires a lot of effort and time. It surely would be better to '''follow parser executed code flow without the need to update it'''. This proves to be impossible without installing and configuring some additional tools. Many of such freely available tools are based on [[En/xdebug]], a software that will be thee subject of a future article dealing with its many features, installation and configuration procedures and bindings with some external developers tools.
+The procedure can result difficult and requires a lot of effort and time. It surely would be better to '''follow parser executed code flow without the need to update it'''. This proves to be impossible without installing and configuring some additional tools. Many of such freely available tools are based on xdebug, a software that will be thee subject of a future article dealing with its many features, installation and configuration procedures and bindings with some external developers tools.
@@ Line 134: / Line 134: @@
 * [http://www.php.net PHP language home page]
-* [http://php.net/manual/it/ PHP language manual]
+* [http://php.net/manual/en/index.php PHP language manual]
 ----
 Languages: '''English''' - [http://www.giustetti.net/wiki/index.php?title=php_debug Italiano]