$RID = "MEH|MED|MMD|MMS|CR1|FR1";

while(<$dpf>) {
    while(m/($RID)(....)(.*)($RID)/g) {
        $RecordID = $1;  $RecordLen = $2; $RecordData = $3;
        if (len($RecordData) != $RecordLen) {
            #ERROR:  Record is wrong length
        }
    }
}

##</code><code>##

MEH0016BUNCHODATA123456MED0019BUNCHMOREDATA456789MED0018MOREDATAAGAIN44568