error_log

Example 267. Basic error_log() usage

// Send an error message to the php error log
error_log ("Uh oh, something bad happened.");

// Mail an error message somewhere
error_log (
    "Uh oh, something bad happened.", 1,
    'admin@example.com', 
    "Subject: Error at $PHP_SELF\nBcc: root@example.com"
);

// Append an error message to a file
$date_time = date ('Y-m-d H:i:s');
error_log ("[$date_time] foo without bar on line 20\n");

Example 268. Send an error message to the default PHP error log

<?php
// Make sure that the log_errors and error_log directives are set
// in the php.ini file. They must be set for the error_log function 
// to be able to write errors to the PHP error log.

// If they're not set, you can set them at runtime by
// uncommenting the two lines below.
// ini_set ('log_errors', 1);
// ini_set ('error_log', 'syslog');

// You can also specify a file for the error log directive.
// ini_set ('error_log', '/var/log/php_error.log');

// Try to retrieve data from a URL.
// In this case, pretend that you have invested in Flag Resources stock
// and want to track the fluctuations in the stock's value.
$URL = 'http://finance.yahoo.com/d/quotes.csv?s=FGRa.V&f=sl1d1t1c1ohgv&e=.csv';

// Try to open a connection to the resource.
// If a connection cannot be opened, log an error to the PHP error log.
// Suppress output of possible errors with the error control operator (@).
if (! $fp = @ fopen ($URL, 'r')) {
    // Log the error
    error_log (sprintf ('Could not open %s in file %s at line %s.',
        $URL, __FILE__, __LINE__ - 2));

    // Exit the script with an error message for the user
    die ("$URL could not be reached.  Please try again later.<br /><br />");
}

// Retrieve all of the data from the URL.
// Suppress possible errors with the error control operator (@).
while (! @ feof ($fp))
    $stock_data .= @ fgets ($fp, 1024);

// Remove any trailing and leading whitespace.
// Add a newline at the end to make sure that
// each new piece of stock data will get its 
// own line.
$stock_data = trim ($stock_data) . "\n";

// Make sure that the data looks right.
// It should be a comma-separated list of values.
if (! ereg ('^([^,]+,)+[^,]+$', $stock_data)) {
    // Log the error
    error_log (sprintf ('Could not read data from %s in file %s at line %s.',
        $URL, __FILE__, __LINE__ - 2));

    // Exit the script with an error message for the user.
    die ("$URL could not be read.  Please try again later.<br /><br />");
}

// Use error_log() to write out the retrieved stock data.
// While this is not what the function was explicitly designed for, 
// this code is a lot shorter than doing the same thing with fopen/fwrite/fclose....
if (error_log ($stock_data, 3, 'FGR.aV'))
    print "Stock data written.";

?>

Example 269. Use error_log to gracefully handle database server outages

<?php
///*** NOTE: This example is geared towards UNIX-like systems ***///

// Configure PHP's error logging support.
// Ideally, these directives should be set in the php.ini file!
ini_set ('track_errors', 1);
ini_set ('log_errors',   1);
ini_set ('error_log',    '/var/log/php_error.log');

// Grab the path to the error log.
$error_log = ini_get ('error_log');

// Try to connect to a MySQL database.
// Suppress possible errors with the error control operator (@).
$db_link = @ mysql_connect ('localhost', 'foo', 'bar');

// Having the database server go down can cripple a dynamic web site.
// Let's try to handle the problem gracefully.
if (! $db_link) {
    // Capture the last error message generated
    $error = $php_error_msg;

    // Log the error
    error_log ($error);

    // Mail the system administrator, however...
    // if the site is busy, we don't want to clog the administrator's mailbox.
    // Let's add a bit of functionality to limit how much mail is generated.

    // Find the last entry containing the error message stored in $error.
    // Use a system command - the built-in system utilities should be much
    // faster at searching a large text file than PHP.

    // Use the exec() function to run the system command.
    // exec() returns the last line of output from the command.
    // Use escapeshellarg() to make the error message safe to use
    // as an argument for a shell command.
    $last_error = exec ('tail --lines=1000 | grep ' . escapeshellarg ($error));

    // If there is no error message that matches $error within the last 15 minutes
    // or 1000 errors, mail the sysadmin.
    if (! trim ($last_error) || time() < strtotime (substr ($last_error, 1, 20)) + 15 * 60) {
        $time = date ('Y-m-d H:i:s');
        error_log (
            "The MySQL server may be down. At $time, script $PHP_SELF encountered this error: $error.",
            1, $SERVER_ADMIN
        );
    }

    // Route the client to an error handling page
    header ('Location: http://www.some.host.com/mysql_error.php');
}
?>