$_ is a special variable which contains the value of the last matched expression
Interesting, where did you get that?
Consider and meditate on the following:
my $string = 'This is a string';
my $match = $string =~ m/string/;
And the following warning:
Use of uninitialized value $_ in say at C:\Data\strawberry-perl\perl\s
+cript-chrome\Perl-1.pl line 9.
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James