Magic Quotes is a process that automagically escapes incoming data to the PHP script. It's preferred to code with magic quotes off and to instead escape the data at runtime, as needed.
When on, all ' (single-quote), " (double quote), \ (backslash) and NULL characters are escaped with a backslash automatically. This is identical to what addslashes() does.
There are three magic quote directives:
Affects HTTP Request data (GET, POST, and COOKIE). Cannot be set at runtime, and defaults to on in PHP.
See also get_magic_quotes_gpc().
If enabled, most functions that return data from an external source, including databases and text files, will have quotes escaped with a backslash. Can be set at runtime, and defaults to on in PHP.
See also set_magic_quotes_runtime() and get_magic_quotes_runtime().
If enabled, a single-quote is escaped with a single-quote instead of a backslash. If on, it completely overrides magic_quotes_gpc. Having both directives enabled means only single quotes are escaped as ''. Double quotes, backslashes and NULL's will remain untouched and unescaped.
See also ini_get() for retrieving its value.
Useful for beginners
Magic quotes are implemented in PHP to help code written by beginners from being dangerous. Although SQL Injection is still possible with magic quotes on, the risk is reduced.
Convenience
For inserting data into a database, magic quotes essentially runs addslashes() on all Get, Post, and Cookie data, and does so automagically.
Portability
Assuming it to be on, or off, affects portability. Use get_magic_quotes_gpc() to check for this, and code accordingly.
Performance
Because not every piece of escaped data is inserted into a database, there is a performance loss for escaping all this data. Simply calling on the escaping functions (like addslashes()) at runtime is more efficient.
Although php.ini-dist enables these directives by default, php.ini-recommended disables it. This recommendation is mainly due to performance reasons.
Inconvenience
Because not all data needs escaping, it's often annoying to see escaped data where it shouldn't be. For example, emailing from a form, and seeing a bunch of \' within the email. To fix, this may require excessive use of stripslashes().
The magic_quotes_gpc directive may only be disabled at the system level, and not at runtime. In otherwords, use of ini_set() is not an option.
Example 30-1. Disabling magic quotes server side An example that sets the value of these directives to Off in php.ini. For additional details, read the manual section titled How to change configuration settings.
If access to the server configuration is unavilable, use of .htaccess is also an option. For example:
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In the interest of writing portable code (code that works in any environment), like if setting at the server level is not possible, here's an example to disable magic_quotes_gpc at runtime. This method is inefficient so it's preferred to instead set the appropriate directives elsewhere.