Update: with regard to It's probably faster to use 2 regexps too: Yes, a quick Benchmarking shows that, with anchoring, the double-regex style runs about 50% faster than the single-regex solution I posted. (Perhaps one of the resident RegEx gurus can explain why this is?)

I'd be interested to see your benchmark (code + data), as I don't come to the same conclusion. The benchmark below shows the one regex solution to be somewhat faster - the data sample is tiny though.

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw /timethese cmpthese/;

chomp (our @lines = <DATA>);

our (@r1, @r2);

cmpthese -10 => {
    one      =>  '@r1 = map {/^\w+(?:,\w+)*$/          ? 1 : 0} @lines
+',
    two      =>  '@r2 = map {/^[\w,]+$/ && !/^,|,,|,$/ ? 1 : 0} @lines
+',
};

die "Unequal" unless "@r1" eq "@r2";


__DATA__
one,two,three,four,five
,one,two,three,four,five
one,two,three,four,five,
one,two,three,,four,five
one,two,three four,five




       Rate  two  one
two 25436/s   -- -26%
one 34417/s  35%   --
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Abigail