they did not give solution of the problem. They are giving only matching the string

The point of these tutorials is to explain to you how things work, so that you can understand them and solve the problems yourself. perlretut tells you enough about regular expressions to enable you to come up with a solution yourself. So don't just skim over it, read it thoroughly, try to understand it. Try things out, play with them.

we have to read the file some other way. but i don't know how it is ?

If line-by-line doesn't work for you, what other options could work? Don't give up so easily!