#!/usr/bin/perl -w

# ...
# I assume @files holds the list of filenames
my %data;

foreach (@files) {
	# this will allow us to store the whole file as a string!
	{
		local $/ = undef; #
		open FILE, $_ or die "Couldn't open $_: $!\n";
		$data{$_} = <FILE>;
		close FILE;
	}
}

# to print :

foreach (sort keys %data) {
	my ($city, $id) = split /_/, $_;
	print "City: $city, ID : $id\n";
	print "====\n\n";
	print $data{$_}, "=====\n";
}