Extract names from many PDF files

Edited on: 20 Jun 2021


  • GNfinder - a scientific names finding app.
  • GNU parallel - a tool for parallel execution of a command (usually it is either already included, or can be istalled via standard package manager for an OS).
  • a folder with several PDF files that contain scientific names.


This tutorial shows how to find scientific names in many PDF files using GNfinder and GNU parallel.

If you need a powerful introduction to the command line itself, most of the commands you will need for this GNfinder exercise, you can learn via this Software Carpentry Unix Shell lesson.

Install gnfinder and parallel

Follow instructions at GNfinder home page for installing the application.

Check if GNU parallel is installed already, if not, follow instructions for your OS how to install it.

Extracting names from documents

To write this tutorial I used a folder with several PDF files in it as an example. First, go to such folder on your own computer and create names folder in it. Note that character designates a command line prompt and is not part of a command.

mkdir names

Now lets examine how many files are in the folder and how big the folder is.

ls *pdf |wc -l
❯ du -hd0
854M .

So my folder contains 558 files and is 854 Megabytes in size.

Now lets use GNU parallel program to extract and verify names from these PDF files. We are going to use the default CSV format for the output.

ls *.pdf | parallel 'gnfinder  {} -v > ./names/{.}.csv'

The first ls *.pdf command returns filenames in the folder that end with .pdf. Then we send the filenames via pipe (|) as an input to a GNU parallel command. The GNU parallel checks how many CPUs the computer has, creates the corresponding number of processes and then executes gnfinder command in parallel for each filename using these processes. The {} in the command is substituted with the name of a file, for example if pipe received the file Hamilton_1983.pdf, the name of this file will be used instead of {} in the command. The {.} is almost the same as {}, but it strips the extension of the file, so Hamilton_1983.pdf gets to Hamilton_1983 and ./names/{.}.csv becomes .names/Hamilton_1983.csv.

Make sure you do not overuse the parallel command, as it might overload Apache Tika server if too many jobs are send to it simultaneously. If such thing happens, you will start to get error messages.

On my computer the process of converting PDF to text and then running name verification took 1 min 21 sec. Lets examine the result:

cd names
❯ ls *csv |wc -l
❯ du -hd0
9.7M .cat * |wc -l

Looks like for every PDF file there is now one CSV file (558 total), the total size of the results is 9.7 Megabytes and there are 700909 rows generated in the output.

Lets look inside one of the files:

head Hamilton_1983.csv
0,(RHYNCHOTA:,Rhynchota,69,80,3.67,1,NO_ANNOT,,,Exact,0,"Rhynchota Schmarda, 1859",Rhynchota,urn:lsid:irmng.org:taxname:1377138,181,IRMNG,
1,HOMOPTERA:,Homoptera,81,91,5.15,1,NO_ANNOT,,,Exact,0,"Homoptera Boisduval in Guenée, 1852",Homoptera,urn:lsid:irmng.org:taxname:1405844,181,IRMNG,
2,CICADELLIDAE),Cicadellidae,92,105,4.81,1,NO_ANNOT,,,Exact,0,Cicadellidae,Cicadellidae,3950452,1,Catalogue of Life,
3,(Macrosteles quadrilineatus,Macrosteles quadrilineatus,1025,1052,11.75,2,NO_ANNOT,,,Exact,0,"Macrosteles quadrilineatus Forbes, 1885",Macrosteles quadrilineatus,2918990,1,Catalogue of Life,
4,"Aphrodes,",Aphrodes,1208,1217,4.76,1,NO_ANNOT,,,Exact,0,Aphrodes,Aphrodes,3971201,1,Catalogue of Life,
5,"Euscelis,",Euscelis,1218,1227,4.12,1,NO_ANNOT,,,Exact,0,Euscelis,Euscelis,4044198,1,Catalogue of Life,
6,"Evacanthus,",Evacanthus,1228,1239,4.99,1,NO_ANNOT,,,Exact,0,Evacanthus,Evacanthus,4044915,1,Catalogue of Life,
7,"Limotettix,",Limotettix,1240,1251,4.75,1,NO_ANNOT,,,Exact,0,Limotettix,Limotettix,4088755,1,Catalogue of Life,
8,"Macrosteles,",Macrosteles,1253,1265,3.62,1,NO_ANNOT,,,Exact,0,Macrosteles,Macrosteles,4094664,1,Catalogue of Life,

It looks like in case of this file the first 9 names were found in one or more biodiversity databases.

Extracting text out of PDF files

It is possible to use GNfinder for extracting UTF8-encoded text out of a large variety of files as well. Go again to the folder with PDF files and use the following commands:

mkdir texts
❯ ls *.pdf | parallel 'gnfinder {} -I > ./texts/{.}.txt'

Lets look at the results:

cd texts
❯ ls *.txt|wc -l
❯ head Hamilton_1983.txt


K. G. A. Hamilton
Biosysternatics Research Institute, Agriculture Canada, Ottawa KIA OC6

Abstract Can. Ent. 115: 473-511 (1983)

Fourteen new records of introduced leafhoppers are added to the 157 leafhoppers pre-

Now that you have textual respresentations of all the PDF files, you can run gnfinder locally on these files without the use of remote services:

ls *.txt | parallel 'gnfinder {} -U > {.}.csv'