The Default Error Handler
If ignore_repeated_errors is enabled, the first thing PHP's error handler does is to check whether the current error message is a repeat of the last one. If it is, or if the origin (file and line) of the error is the same and ignore_repeated_source is also enabled, PHP does exactly as the ini option suggests it would: It ignores the error and continues processing, or halts execution if the error was fatal.
Further handling of the error depends on the setting error_reporting, which tells PHP which errors should be handled and which should be ignored outright. The error_reporting directive is a bit mask made up of zero or more of the error levels mentioned earlier joined together using the bitwise operations. Note, however, that core errors (E_CORE_WARNING and E_CORE_ERROR) cannot be ignored using this setting. PHP's internal error handler will always continue handling them.
error_reporting=E_ERROR | E_CORE_ERROR | E_COMPILE_ERROR | E_PARSE | E_USER_ERROR
The setting above tells PHP's default error handler to deal only with fatal errors and to ignore everything else. We could have left E_CORE_ERROR out of the preceding list because it's never ignored, but it's best to be explicit where possible to avoid any unexpected behavior down the road. Informational and actionable errors will have no effect.
error_reporting = E_ALL
The E_ALL constant is a special value that represents every error level except E_STRICT. With this line in your php.ini, all error conditions except E_STRICT messages will be handled by the default error handler.
error_reporting = E_ALL & ~E_NOTICE
The default php.ini settings for error reporting include all error types except E_STRICT and E_NOTICE using the preceding syntax. The symbols given translate in human speak to "E_ALL and not E_NOTICE," or "Everything that's normally part of E_ALL except for E_NOTICE." Because E_ALL already excludes E_STRICT, this gives us all fatal and actionable errors, plus the user-generated informational error E_USER_NOTICE.
After it has decided whether to handle a particular error, PHP needs to know what to do with it. The settings display_errors and log_errors can be enabled to output a formatted message and/or write a message to an error_log, respectively. display_errors will not, by itself, display errors that occur during startup. To show startup errors, you must enable both display_errors and display_startup_errors. However, many administrators prefer to find startup errors in the error_log.
Errors can be output by display_errors in one of three formats: plain text, HTML, and XML. By default, PHP scripts run from the command line will output in plain text, whereas scripts run via a Web server will output in HTML.
<?xml version="1.0"?> <methodResponse> <fault> <value> <struct> <member> <name>faultCode</name> <value><int>2</int></value> </member> <member> <name>faultString</name> <value> <string>Warning: Unable to open myfile.txt for reading in /home/ jdoe/public_html/myscript.php on line 42</string> </value> </member> </struct> </value> </fault> </methodResponse>
<br /> <b>Warning</b>: Unable to open myfile.txt for reading in <b>/home/jdoe/public_html/ myscript.php</b> on line <b>42</b><br />
If html_errors is not enabled, the same message is output, but without the markup tags. The plain text and HTML versions will also add the contents of error_prepend_string and error_append_string to the beginning and end of the message output respectively.
Next, if log_errors is enabled, PHP will construct an error message similar to the plain-text version, but not including the error_prepend_string or error_append_string values, and append it to the end of the file specified by error_log. If error_log is empty, PHP will ask your Web server to handle it, or output it to stderr when using the CLI or CGI versions of PHP. If error_log is set to syslog and your system supports the concept of a syslog, it will be used; otherwise, PHP will attempt to open the filename provided and append the error string to its contents.
bool error_log(string $message[, int $message_type[, string $destination[, string $extra_headers]]])
When none of the optional parameters are specified, or when 0 is given for message_type, error_log() sends its message to the same error log used by PHP's internal error handler (as described previously and depending on the value of the php.ini option error_log). error_log() may also be used to send email or append to an alternative log file. See the online manual for more information on the usage of error_log().