PHP CURL GET request returns 500 where bash curl s

Question

I'm attempting to use PHP's CURL to make a GET request to a server and am having some difficulties doing so. When I make the request through PHP I am returned a 500 error from the external server. However, if I make the request using the bash curl, or visit the URL in a browser it succeeds.

I've stripped the PHP down to the bare essentials:

$url = 'http://example.com:8080/path/to/service?cmd=my_command&arg=example2.com';
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_exec($ch);
print_r(curl_getinfo($ch));
curl_close($ch);

As stated this returns a 500 error from example.com. However, if I do the following:

[me@host ~] curl "http://example.com:8080/path/to/service?cmd=my_command&arg=example2.com"

I am returned the expected XML document.

What gives? It's got to be something with the encoding of the URL, as if I strip the $url var down to just http://example.com:8080 the PHP CURL request now responds with 200. I've tried replacing the & with %26 - that didn't work (nor would I expect it to, as & is valid in the URL there). I've tried doing what the answer for php curl sending vars using GET wierd results suggested, but that didn't help either.

What am I missing here? I'm sure that it's something absurdly simple, but it's escaping me.

Thanks!

EDIT: I've just attempted doing this in Python - just to see what happened - and it works fine there:

import urllib2
r = urllib2.urlopen(theURL)
r.read()

Answer 1

It turns out that the API I was accessing required a User-Agent for all requests, but did not provide any information to indicate such.

Is this a common thing? I can't find any other examples of anyone else doing this other than http://developer.github.com/v3/#user-agent-required

I was able to get things working just fine by adding

curl_setopt($ch, CURLOPT_USERAGENT, "User-Agent: Some-Agent/1.0");