Re: First Question, why something works? (-M)

[toolic]

-M uses $_. Tip #6 from the Basic debugging checklist ... B::Deparse

sub BEGIN {
    use warnings;
    use strict 'refs';
    require 5.01;
}
use warnings;
use strict 'refs';
BEGIN {
    $^H{'feature_say'} = q(1);
    $^H{'feature_state'} = q(1);
    $^H{'feature_switch'} = q(1);
}
die "No file names supplied!\n" unless @ARGV;
my $oldest_name = shift @ARGV;
my $oldest_age = -M $oldest_name;
foreach $_ (@ARGV) {
    my $age = -M $_;
    ($oldest_name, $oldest_age) = ($_, $age) if $age > $oldest_age;
}
printf "The oldest file was %s, and it was %.1f days old\n", $oldest_n
+ame, $oldest_age;

See also How do I compose an effective node title?

[i255d]

So what you are saying is that when I use $age = -M; in my foreach loop, it is the same as me using $age = -M $_;?

[Athanasius]

Hello i255d, and welcome to the Monastery!

Yes, this is one of many places where Perl uses the special $_ variable implicitly, making it easier to write concise, elegant code. For a list of the places where Perl uses $_ implicitly, see the first entry in perlvar#General-Variables. (If you’re not already familiar with the Perl documentation site, bookmark it now and get to know your way around as soon as possible.)

The Camel Book (4^th Edition, p. 706) has this advice:

Use the singular pronoun to increase readability:

   for (@lines) {
       $_ .= "\n";
   }

The $_ variable is Perl’s version of a pronoun, and it essentially means “it”. So the code above means “for each line, append a newline to it.”

Hope that helps,

[i255d]

Very excited to be part of the Monastery. I am still on the llama book, chapter 13. Looking forward to the next one. I am an administrator, so I felt it best not to rush through the file and directory sections of this book. Yes, I think you have answered my questions. I see someone ran my code through B::Deparse, later I will have to get into what that is.

[Laurent_R]

Yes. If the argument is omitted, file test operators test $_ (except -t which tests STDIN).