One of the first things Carp does is local($!, $^E), I assume because of what its documentation says: "Carp takes care not to clobber the status variables $! and $^E in the course of assembling its error messages." I think what's going on is that since @_ are aliases, this actually clears out the argument as well. Another thing to note is that $! is like a dualvar, though I'm not sure if this has to do with the issue. <update> Actually, in the following, $? behaves the same way as $!, while $@, an our variable, and an explicitly created dualvar do not - so it probably does have to do with the variable's magic in combination with local instead. </update> I suspect you'll have to work with "$!". This reproduces the issue:

use warnings;
use strict;
use Data::Dump;

sub foo {
    dd @_;
    local $!;
    dd @_;
}

$! = 2;
foo($!);
$! = 2;
foo("$!");

__END__

"No such file or directory"
""
"No such file or directory"
"No such file or directory"

[download]

In reply to Re: Carp: $! vs "$!" in croaking (updated) by haukex
in thread Carp: $! vs "$!" in croaking by cavac

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.