Thanks! I see you're filtering lines beginning with # when they occur at the beginning of the file; the way I understood the OP's sample data is that the comments can occur anywhere. And my worry was that, even though in the OP's data this is probably not the case, filter-based solutions will remove lines that may actually not be comments, and I wasn't sure if there was a easy solution for this?

use warnings;
use strict;
use Data::Peek;
use Text::CSV_XS qw/csv/;

DDumper csv( in=>*DATA, escape_char=>"\\",
    filter => sub { $_[1][0] !~ m/^\s*#/ });

__DATA__
# This is a comment
a,b,c

# Also a comment
x,y,z
"#not",a,comment
\#also,not,"a comment"
[download]

Output:

[
    [   'a',
        'b',
        'c'
        ],
    [   ''
        ],
    [   'x',
        'y',
        'z'
        ],
    [   ''
        ]
    ]
[download]

So more or like like this:?

DDumper csv (
    in     => *DATA,
    sep    => "|",
    filter => sub {
        $_[1][0] =~ m/^\s*#/ && @{$_[1]} == 1 ? 0 : 1;
        },
    );
[download]

Which would not even need a ternary if slightly rewritten


Enjoy, Have FUN! H.Merijn

So more or like like this:?

Closer, but then this no longer filters comments that contain the sep character (e.g. add "# This is a comment, too" to my example above)...

Update: I realize this is less likely when sep=>'|', but my question is basically whether there's a "generic" way to filter lines. For example, I could load the file into memory and do s/^\s*#.*(?:\n|\z)//mg, but that would break any CSV data that contains embedded newlines that happen to match this pattern. In other words, with Text::CSV_XS, filter is only applied after parsing fields like "#foo" or \#foo to #foo, and I'm wondering if there's a hook into the parser before that takes place?

Update 2: In the CB, you suggested in => \do { local $/; <DATA> =~ s/^\s*#.*(?:\n|\z)//mgr }, which gets closer as well, though it breaks this test case. Just for completeness, here are all the test cases so far combined into one data set:

# This is a comment
not,a,comment

# This is a comment, too
not,a,comment
"#not",a,comment
\#also,not,"a comment"
foo,"bar
# Not a comment, either!
quz",baz
[download]