What the output is ?
I'll skip this one - it takes nothing to put the text inside a text file, and execute it using the Perl interpreter.
perlrun can help you with this, anyway.
Explanation ?
For regex in general, the main reference is
perlre, but a look to
perlretut is worth a look as well. In your case,
perlop is also a good starting point, in particular the "Regexp Quote-Like Operators".
In general, the "s/SOMETHING/OTHER/" construct makes substitutions. Wherever it finds "SOMETHING", it puts "OTHER". In this case, this substitution operator is applied to the $value variable, via the =~ binding operator. This can be found in perlop, of course.
The "e" switch indicates that the "OTHER" (i.e. the 'pack("C", hex($1))' in your case) is to be considered an expression and not a pure sequence of characters, and the "g" switch indicates that the substitution has to be applied to every occurence of the text matched in the first "SOMETHING" part (i.e. the '%(..)' in your case). Globally, this seems born to replace every occurrence of "%XX" with the character whose hexadecimal representation is "XX".
Could any one help me .......
A whole lot is willing to help you here. But please take a look around, and in particular to the
About the PerlMonks FAQ and
How do I post a question effectively?. You forgot to use proper code tagging, and forced a janitor to do it for you. Welcome to the Monastery!
Flavio
perl -ple'$_=reverse' <<<ti.xittelop@oivalf
Don't fool yourself.