use Archive::Zip qw(:CONSTANTS :ERROR_CODES);
use IO::Scalar;

my $fname = 'file1.txt';
my $zipfile = 'filename.zip';
my $zip = Archive::Zip -> new();
if (-e $zipfile)
{
   $zip ->read($zipfile);
} 

my $member = $zip->memberNamed( $fname );
if ($member eq undef)
{
   $member = $zip->addFile( $fname );
}

$member -> desiredCompressionLevel( 9 );

$fname = 'autotransParams.txt';
$member = $zip->memberNamed( $fname );
if ($member eq undef)
{
   $member = $zip->addFile( $fname );
}

$member -> desiredCompressionLevel( 9 );
my $status = $zip -> overwriteAs($zipfile);