Programming, like the real world, often involves unforeseen happenings that disrupt the flow of events. In programmer’s lingo, these unexpected happenings are known as exceptions.

We can read a file by using the following file modes :
           R, r+, w+, a+.

There are two types of key of array. It can be numerical And associative.
Numerical :It stores each array element with numeric index name.
associative : It contains characteristic element or string index name.

Regular expressions provide the foundation for describing or matching data according to defined syntax rules. A regular expression is nothing more than a pattern of characters itself, matched against a certain parcel of text.

We can read a file using the following methods and  modes:

Methods: file(), file_get_contents(), fgetcsv(), fgets(), fgetss(), fgetc(), fread(), readfile(), fscanf().

Modes: R, r+, w+, a+, x+.