reading in arguments

Hi. I was wondering why the code below works but it won't work if I change the line

my $file = shift;

to

my $file = @_;

and also, if I run this code (using the name cat.pl) with a comma separated list of arguments why it skips the first argument. For example if I run
perl cat.pl SampleForGraphing.csv, second.csv

it only prints the file second.csv

Thanks.

#!/Perl/bin/perl
use strict;
#use warnings;

sub print_file {
my $file = shift;

open FILE, $file;
while (my $line = <FILE>) {
print $line;
}
}
sub cat {
	while (my $file = shift) {
			print_file $file;

}
}
cat @ARGV;

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