Try this: 
sub is_valid_string
{
    my $string = shift;

    # Handle the empty case
    return 0 unless length $string;

    # Preserve trailing empty fields
    my @string = split ',', $string, -1;

    # No commas at the beginning, end, or next to one another.
    return 0 if grep { !$_ } @string;

    return 0 if grep { /[^a-zA-Z]/ } @string;

    return 1;
}

[download]

It was tested with your test strings and passed with flying colors.

------
We are the carpenters and bricklayers of the Information Age.

The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

In reply to Re: regex: only want [a-zA-Z] and comma chars in a string (Don't use a regex!) by dragonchild
in thread regex: only want [a-zA-Z] and comma chars in a string by heezy

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