Regular expressions provide the foundation for describing or matching data according to defined  syntax rules. Generelly regular expressions declared by "/^[value]{range}$/";.

Magic methods are the members functions that is available to all the instance of class Magic methods always starts with "__". Eg. 
__construct All magic methods needs to be declared as public To use magic method they should be defined within the class or program scope Various Magic Methods used in PHP 5 are: __construct() __destruct() __set() __get() __call() __toString() __sleep() __wakeup() __isset() __unset() __autoload() __clone()

We can read a file using the following mode and Methods:-
Methods- file(), file_get_contents(), fgetcsv(), fgets(), fgetss(), fgetc(),fresd(), readfile(), fscanf().  
Mode-  R, r+, w+, a+, x+

Ans:  The substr() function is used to return the part of a string located between a predefined starting offset and length position.
Its prototype follows:
string substr(string str, int start [, int length])

We can write into a file using the following mode and Methods:
Methods- fwrite() with fopen, file_put_contants().   
Mode-  r+,  W,  w+, A, a+, X, x+