I haven't yet gotten to the point of running it from cron; so far I'm still testing it on the command line, but it's successfully writing these files, so permissions don't seem to be a problem.

I have the minimal test reading successfully from cURL, and doing everything that the main script is doing to the Parser object.

#!/usr/bin/perl

use strict;
use Data::Dumper;
use Net::Curl::Easy qw(:constants);
use XML::RSS::Parser;

my $ua_string = "User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; r
+v:30.0) Gecko/20100101 Firefox/30.0";
my $curl = Net::Curl::Easy->new;
my $feedsrc = "https://feeds.simplecast.com/o4MKcfjK";
my $feed;

$curl->pushopt(CURLOPT_HTTPHEADER, [$ua_string]);
$curl->setopt(CURLOPT_NOPROGRESS, 0);
$curl->setopt(CURLOPT_FOLLOWLOCATION, 1);
$curl->setopt(CURLOPT_CONNECT_ONLY, 0);
$curl->setopt(CURLOPT_URL, $feedsrc);
$curl->setopt(CURLOPT_WRITEDATA, \$feed);
$curl->perform();

my $parser = XML::RSS::Parser->new();
$parser->register_ns_prefix('lc_itunes', 'http://www.itunes.com/dtds/p
+odcast-1.0.dtd');
my $rss = $parser->parse_string($feed);
print $rss . "\n";
[download]

$ ./test.pl 
  % Total    % Received % Xferd  Average Speed   Time    Time     Time
+  Current
                                 Dload  Upload   Total   Spent    Left
+  Speed
100  164k  100  164k    0     0  1267k      0 --:--:-- --:--:-- --:--:
+-- 1271k
XML::RSS::Parser::Feed=HASH(0x618af3317380)
[download]

So that's working. I just can't see why it's breaking as part of the actual script, when it's clearly readable in isolation, and works fine on a different machine.