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if($chunk_size=~/(\d+)([mMgG])/) {
    my $numb=$1;
...
else {
    $size=$chunk_size;
}

if ( $chunk_size =~ /(\d+)g/i )
{
...
{
    $size = $chunk_size;
}

$size = $chunk_size =~ /(\d+)g/i ? $1 * 1024*1024*1024 :
        $chunk_size =~ /(\d+)m/i ? $1 * 1024*1024 :
        $chunk_size =~ /(\d+)k/i ? $1 * 1024 :          # easy additio
+n
        $chunk_size;