The "$_" variable is described in perlvar. It's the default variable for many operators and functions.

This bit of code uses a variable:

while (my $line = <INFILE>) {
    print $line;
    print "FOUND IT!\n" if $line =~ /foo/;
}
[download]

But if we wanted to use $_, we could rewrite the code as:

while (<INFILE>) {
    print;
    print "FOUND IT!\n" if /foo/;
}
[download]

It's a very handy variable, but I only tend to use it in very small areas. I often find using a variable name to be a bit more clear and simple (for me) to maintain.

...roboticus