I wrote this for debug php purpose.
In LAMP, there are 2 types of output:

1. standard output (stdout, file descriptor: 1)
   We output the information data to standard output, it is the default mode when we use echo, print.
2. standard error (stderr, file descriptor: 2)
   When errors occurs, the error messages write to it. In command line environment, it is the same as standard output (stdout=stderr), but it differs in other cases.
   in Apache web server, the standard output redirects to $log/access.log, while standard errors to $log/error.log.

For standard output, the data can be buffered or not:

• By using ob_start(), fwrite() functions to buffer the data. This delays the operation, but improves the input/output performance.
• If not useing buffering, fwrite() functions directly operate I/O, without delay (although frequent I/O operation could decrease the performance).

In production environment, for security reason, we suppress the error message on failure by prepending a @ to the function name.
e.g, @mysql\pconnect($host, $username, $password);_

In developing environment, the output is very important for testing and debug purpose which we can’t disable or ignore.
There are 3 type of output:

(a) To system logfile, e.g, for Apache’s logfiles: error.log and access.log.
It is very useful for test and debug purpose, e.g, we use:
$ tail -f error.log
$ tail -f access.log
to monitor errors and standard output in real time;
or:
$ tail -n 20 error.log
to monitor error.log last 20 lines.

(b) self-defined log to hold output: We can create a file and ouput useful data into our file to monitor the programs.
$file = fopen(“my.log”, “w”);
fwrite($file, $message);
fclose($file);

(c) to screen (browser):
We have 3 common functions for output to screen purpose:

1. echo, or print - simply output scalar variable
2. print_r - Prints human-readable information about a variable
3. var_dump - Dumps information about a variable

The built-in echo is suitable for scalar variables, while print_r() is for array(). var_dump() is a little super, could replace print_r() when necessary.
The following function is a little smart to decide output format according to $variable itself: scalar or array().
If scalar, using echo. If array, using print_r() to output.

1. function output($var)
2. {
3. if (is_array($var)) {
4. echo ”

   “;

5. print_r($var);
6. echo ”“;
7. }
8. else {
9. echo $var . ”
   n”;
10. }
11. }

If your output is a complex sql in the browser, using the following:
echo ”

”. $sql . ”

The following is a better solution for output in browser. It does some css works to make the output well-formatted and esay-reading.
I used it in my various applications to generate formatted output when warnings or errors occur.
The entry point is: dump($message\to_output, $info);_

• every time the dump($message_to_output) is called.
• $info is the title of the message. It is optional.
• do_dump() is internal called, don’t need to call it directly.

The following are the functions:

1. function dump(&$var, $info=FALSE)
2. {
3. $scope = false;
4. $prefix = ‘unique’;
5. $suffix = ‘value’;
6. if($scope) $vals = $scope;
7. else $vals = $GLOBALS;
8. $old = $var;
9. $var = $new = $prefix.rand().$suffix; $vname = FALSE;
10. foreach($vals as $key => $val) if($val === $new) $vname = $key;
11. $var = $old;
12. echo ”

    “;

13. if($info != FALSE) echo ”$info:
    “;
14. do_dump($var, ’$‘.$vname);
15. echo ”“;
16. }
17. function do_dump(&$var, $var_name=NULL, $indent=NULL, $reference=NULL)
18. {
19. $do_dump_indent = ”|    “;
20. $reference = $reference.$var_name;
21. $keyvar = ‘the_do_dump_recursion_protection_scheme’; $keyname = ‘referenced_object_name’;
22. if (is_array($var) && isset($var[$keyvar]))
23. {
24. $real_var = &$var[$keyvar];
25. $real_name = &$var[$keyname];
26. $type = ucfirst(gettype($real_var));
27. echo “$indent$var_name $type = &$real_name
    “;
28. }
29. else
30. {
31. $var = array($keyvar => $var, $keyname => $reference);
32. $avar = &$var[$keyvar];
33. $type = ucfirst(gettype($avar));
34. if($type == “String”) $type_color = ”“;
35. elseif($type == “Integer”) $type_color = ”“;
36. elseif($type == “Double”){ $type_color = ””; $type = “Float”; }
37. elseif($type == “Boolean”) $type_color = ”“;
38. elseif($type == “NULL”) $type_color = ”“;
39. if(is_array($avar))
40. {
41. $count = count($avar);
42. echo “$indent” . ($var_name ? “$var_name => ”:"") . ”$type ($count)
    $indent(
    “;
43. $keys = array_keys($avar);
44. foreach($keys as $name)
45. {
46. $value = &$avar[$name];
47. do_dump($value, ”[‘$name’]”, $indent.$do_dump_indent, $reference);
48. }
49. echo “$indent)
    “;
50. }
51. elseif(is_object($avar))
52. {
53. echo “$indent$var_name $type
    $indent(
    “;
54. foreach($avar as $name=>$value) do_dump($value, “$name”, $indent.$do_dump_indent, $reference);
55. echo “$indent)
    “;
56. }
57. elseif(is_int($avar)) echo “$indent$var_name = $type(“.strlen($avar).“) $type_color$avar
    “;
58. elseif(is_string($avar)) echo “$indent$var_name = $type(“.strlen($avar).“) $type_color”$avar”
    “;
59. elseif(is_float($avar)) echo “$indent$var_name = $type(“.strlen($avar).“) $type_color$avar
    “;
60. elseif(is_bool($avar)) echo “$indent$var_name = $type(“.strlen($avar).“) $type_color”.($avar == 1 ? “TRUE”:“FALSE”).”
    “;
61. elseif(is_null($avar)) echo “$indent$var_name = $type(“.strlen($avar).“) {$type_color}NULL
    “;
62. else echo “$indent$var_name = $type(“.strlen($avar).“) $avar
    “;
63. $var = $var[$keyvar];
64. }
65. }