Why not let Perl write the regex for you?
use Modern::Perl '2014';
use Algorithm::Permute;

my @elements = qw/ A C T G /;
my @permutations;
Algorithm::Permute::permute { push @permutations, ( join '(?:', @eleme
+nts ) . ')?)?)?'} @elements;
my $regex = join '|', @permutations;
$regex = qr/^(?:$regex)$/;

say "Testing";

for my $length ( 1 .. 4 ) {
    my $p =
      new Algorithm::Permute( [ qw/ A C T G A C T G A C T G A C T G X 
+/, ' ' ],
        $length );
    while ( my @res = $p->next ) {
        my $test = join( '', @res );
        print "$test\t";
        say $test=~ /$regex/ ? 'Accept' : 'Reject';
    }
}

[download]
Sample output:
Testing
A    Accept
C    Accept
T    Accept
G    Accept
(...)
X    Reject
     Reject
CA    Accept
AC    Accept
TC    Accept
CT    Accept
(...)
GA    Accept
AA    Reject
CC    Reject
(...)
AG    Accept
XC    Reject
CX    Reject
XT    Reject
(...)
CTGA    Accept
TCGA    Accept
TGCA    Accept
TGAC    Accept
CAGA    Reject
ACGA    Reject
(...)

[download]
The final regex for your pattern will then be /^$regex\s*,\s*$regex$/

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

My blog: Imperial Deltronics

In reply to Re: Regular expression for a comma separated string by CountZero
in thread Regular expression for a comma separated string by naderra

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