sub gzip {
    my $cmd = shift;
    my $dir = shift;
    my ($file, $fullfile);
    my @files = ();
    print "$cmd files in $dir...\n";

    # Make sure command is secure and predictable.
    if ( $cmd eq 'zip' ){
        $cmd = 'gzip';
    } elsif ( $cmd eq 'unzip' ){
        $cmd = 'gunzip';
    } else {
        warn "zip or unzip command not given $!";
    }

    # Generate list of files
    opendir DIR, $dir or warn "Cannot open $dir $!";
    while ( defined ( $file = readdir(DIR) ) ){

        $fullfile = "$dir/$file";
        next if ( !-f $fullfile
                || $file =~ m/\.txt$/
                || $file !~ m/^[\w-]+(\.[\w-]+)*$/ );

        push @files, $fullfile;
    }
    closedir DIR;

    # Using file list from above, issue zip or unzip command.  You cannot do
    # both in the same loop as the readdir may pickup the newly created files
    # and try to process them.  Thus you may endup to zipping a zipped file or
    # unzipping an upzipped file.
    while (<@files>) {
        system ( "$cmd $_") == 0 or warn "Cannot $cmd $fullfile : $!";
    }
}