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Old 06-18-2018, 11:56 PM   #1
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Location: Cambridge

Join Date: Apr 2012
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Default Entrez esearch.fcgi large set of sequences download: fluctuating number of sequences

Hello everybody!

I have a little problem: I'm trying to download a large set of fasta sequences from Entrez, but the number of sequences retrieved differs from the announced number:
When I am using the link in a browser:
It will give me a certain number of sequences.
But when I use the perl script (as explain here:, the number of final fasta sequences is always lower...
I am using just a small difference compared with the tutorial:
        $efetch_url = $base ."efetch.fcgi?db=nucleotide&WebEnv=$web";
        $efetch_url .= "&query_key=$key&retstart=$retstart";
        $efetch_url .= "&retmax=$retmax&rettype=fasta&retmode=text";
Does anybody had the same problem before? Does anybody know where does it come from and how to fix it?

Thanks in advance,
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Old 06-21-2018, 06:01 AM   #2
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Ok, I found the problem: DO NOT USE eUtils !

Use Entrez Direct instead, It's really working (be sure to install the latest NCBI version and not the aptitude package)
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Old 06-21-2018, 06:21 AM   #3
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Posts: 6,978

NCBI requires use of API tokens with eUtils as May 1st, 2018. It you are running a large amount of queries some of those may fail, which may explain the variable numbers. Just a thought.

Last edited by GenoMax; 06-21-2018 at 06:26 AM.
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entrez id

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