Month: July 2010

If you have mysqli extension installed with PHP and you use it to perform database operations, after you have tried to connect to MySQL by:

$conn = new mysqli('localhost', 'db_user', 'db_pwd', 'db_name');

You can then check if the connection is successful by:

if ($conn -> connect_errno) {
  // failure
} else {
  // success
}

That’s because connect_errno contains the error number of the last query. If there’s no error, it’s 0 by default. If an error occurred in the last query, it’s a natural number greater than zero. There you go with the conditional check of whether the PHP database connection is successful.

However if you are using the legacy mysql extension to connect to MySQL databases:

$conn = mysql_connect('localhost', 'db_user', 'db_pwd');

It’s even simpler. The returned value of mysql_connect() function will be FALSE should the connection fail. Therefore, you can check if the connection is successful by:

if ($conn = mysql_connect('localhost', 'db_user', 'db_pwd')) {
  // success
} else {
  // failure
}

If the website is run on a Linux server, everything that can be run from the web (i.e., from the browser address bar) can be run from the Linux console. That is if you have the SSH access which most hosts provide. Connect to your hosting server via SSH by putty and you will have the ultimate control over your box. For example, you can execute a PHP script called routine.php via SSH by:

/usr/bin/php5 routine.php #routine.php is in the current working directory

Depending on your distro and PHP installation options, the command line interpreter (in this case, /usr/bin/php5) may vary in location.

You can add this line to a crontab job and it the PHP script routine.php will be executed by your designated intervals or at any certain time, automatically.

Other than calling PHP scripts from Linux console via SSH, you can also call to execute PHP code in another script file from the current PHP file. For instance, in A.php:

exec('/usr/bin/php5 B.php');

As it obviously suggests, this line will run the Linux command ‘/usr/bin/php5 B.php’ and you can put stuff in B.php that will be taken care of when this line in A.php is executed.

There are a variety of different PHP functions that perform essentially the same task, running system commands: exec, shell_exec, system and passthru.

Sometimes you need to temporarily halt the code execution of your PHP script for certain seconds and then automatically resume it. For example, some mail delivery servers have the restriction that you have to wait a certain interval such as 12 seconds before sending another email.

You can tell your PHP script to stop for 12 seconds before continuing down with the rest of the code by sleep() function:

sleep(12); // freeze PHP execution for 12 seconds before going ahead

That’s it. When it is executed to this line, PHP will freeze for 12 seconds, doing nothing, and then go on with the line immediately after this line.