The following should validate what you specified: 
while (<DATA>) {
    if (/^[CETLMNPA](?:,[CETLMNPA])*$/) {
        print "Validated: $_";
    } else {
        print "Incorrect: $_";
    }
}

__DATA__
C,M,N
C,MN
C,,M,N
P
T
Z
E,M,N,P,A,A

[download]
- Miller

PS: It would be great if you spell checked your node title :)

In reply to Re: Regular expression for combination of data by wind
in thread Regular expression for combination of data by isha

Title:
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