You are on th right track. Gropuing lets you have alternatives

if ( /.*(\d+\.\d+\.(\d\d+|[4-9])\.\d+).*/ )  {
         print "$1 <br> \n";
}
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This matches either a multidigit number or a single digit in 4..9. Note it could still be fooled by 01, etc, so check your input for that problem.