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Reference - What does this symbol mean in PHP?
What does @ mean in PHP?
I have a line in my code which looks like this:
@mysql_select_db($dbname) or die( "Error: Unable to select database");
It works, but I want to know what the @ does and why it is there.
The @ symbol suppresses any errors and notices for the expression it precedes.
See this reference: PHP Error Control Operators
PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.
In this case, the @ will suppress the regular PHP database connection error (which may contain sensitive information). In case of a connection error, the "or die" part will be executed, failing with a generic error message. The line is probably copied from a "quick and dirty" example.
Using the error suppression operator @ is considered bad style, especially when other forms of error handling are missing. It complicates debugging - how can you find out about in error without any indication that it occured? In a production system it's better to log all errors to a file and suppress the rendering of errors on the page. You could do that in the php.ini file or (if you are on a shared host and not allowed to make config changes) with the following code.
ini_set('display_errors', false); ini_set('log_errors', true); ini_set('error_log', '/var/log/apache/php-errors.log'); 
It suppresses all error output. Generally, you shouldn't use it unless you have a good reason. I don't know why it is used in the example you posted, or why die() is used. The error should be caught and processed accordingly. The select may fail for a number of reasons, some perhaps recoverable. Like no connection to the database established.
