in reply to Anti-Virus Signature Updates

Finding the intersection of two arrays is described in perlfaq 4. The short version: use a hash. So incorporating fruitures notes from above, here is my (untested, since I do not have access to a suitable ftp server) try:
#!/usr/bin/perl -w use strict; use Net::FTP; my $host = ''; my $user = 'anonymous'; my $pass = ''; my $remote_dir = '/pub/antivirus/NAV/signatures'; my $destination_dir = 'current-sig';
Here I read the contents of lastupdate.txt into the array @lupd. If the file does not exist, @lupd will be left empty (no need for a special flag).
my @lupd = (); if(-e "./lastupdate.txt") { open(LASTUPDATE,"./lastupdate.txt") or die "Error while opening lastupdate.txt ($!)"; chomp( @lupd = <LASTUPDATE> ); close(LASTUPDATE); }
The following construct is called a hash slice. It is described in more detail in this page
my %haveit; @haveit{ @lupd } = (1) x @lupd; my $ftp = Net::FTP->new($host, Debug => 1); $ftp->login($user,$pass); $ftp->type("I"); my @listing = grep /x86\.exe$/i, $ftp->ls($remote_dir); my @newupdate; foreach my $file (@listing) {
The hash slice above produced a hash which maps every known filename to a true value. So if the file has already been downloaded, we can simply skip the download. When the download is unsuccessful, the file is skipped as well.
next if $haveit{ $file }; $ftp->get($file) or next; push @newupdate, $file; } $ftp->quit; open(NEWUPDATE,">>./lastupdate.txt") or die "Couldn't open lastupdate.txt for appending ($!)"; print NEWUPDATE map "$_\n", @newupdate; close(NEWUPDATE) or die "Closing lastupdate.txt failed ($!)";
You might also want to think about locking if there is any chance that two instances of this program run at the same time.