I am trying to download FASTA sequences from a list of protein GIs (~ 100000). I planned to use EPost using HTTP POST to first upload the list of GIs and then use EFetch to download the FASTA.

I am getting no response from the server (WebEnv and query_key are not generated) when I upload the list of GIs with EPost using HTTP POST.

The code that I am using for EPost is :

#!/usr/bin/perl 
use LWP::Simple; 
use LWP::UserAgent; 

$base = 'http://eutils.ncbi.nlm.nih.gov/entrez/eutils/'; 
$url = $base . "epost.fcgi"; 

$url_params = "db=protein&id=830003112&id=830003110&id=830003108&id=830003106&id=830003104&id=830003102&id=830003100&id=830003098&id=830003096&id=830003094&id=830003092&id=830003090"; 

#create HTTP user agent 
$ua = new LWP::UserAgent; 

#create HTTP request object 
$req = new HTTP::Request POST => "$url"; 
$req->content_type('application/x-www-form-urlencoded'); 
$req->content("$url_params"); 

#post the HTTP request 
$response = $ua->request($req); 
print $response->content;

This prints nothing after the code is run. Ideally it should print the WebEnv and the query_key. The HTTP status is OK and the code is 200.

If I change the url_params and remove all GIs from it

$url_params = "db=protein";

I get the following output :

<?xml version="1.0"?>
<!DOCTYPE ePostResult PUBLIC "-//NLM//DTD ePostResult, 11 May 2002//EN" "http://www.ncbi.nlm.nih.gov/entrez/query/DTD/ePost_020511.dtd">
<ePostResult>
    <ERROR>Empty ID list; Nothing to store</ERROR>
</ePostResult>

I have no idea what the problem is and why the server isn't generating WebEnv and query_key.

If anyone knows the solution please help me out.