sub map_user_group
{
    if( ! defined( $uid ) ){
        if( $user =~ /^\d+$/ ){
            # User is just a number - presume it is the uid
            $uid = $user;
        }
        else {
            $uid = (getpwnam( $user ))[ 2 ];
        }
    }
    if( ! defined( $gid ) ){
        if( $group =~ /\d+$/ ){
            # Group is just a number - presume it is the gid
            $gid = $group;
        }
        else {
            $gid = (getgrnam( $group ))[ 2 ];
        }
    }
}
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Any ideas would be much appreciated!