Catmandu::Introduction - An Introduction to Catmandu data processing toolkit


Catmandu is a data processing toolkit developed as part of the LibreCat project. Catmandu provides the command line client catmandu and a suite of tools to ease the import, storage, retrieval, export and transformation of data. For instance, to transform a CSV file into JSON use the command:

    $ catmandu convert JSON to CSV < data.json

Or, to store a YAML file into an ElasticSearch database type (requires Catmandu::ElasticSearch):

    $ catmandu import YAML to ElasticSearch --index_name demo < test.yml

To export all the data from an Solr search engine into JSON type (requires Catmandu::Solr):

    $ catmandu export Solr --url http://localhost:8983/solr to JSON

With Catmandu one can import OAI-PMH records in your application (requires Catmandu::OAI):

    $ catmandu convert OAI --url --set allFtxt

and export records into formats such as JSON, YAML, CSV, XLS, RDF and many more.

Catmandu also provides the small scripting language "Fix" to manipulate data, extract parts of your dataset and transform records. For instance, rename fields with the move_field Fix command:

    $ catmandu convert JSON --fix 'move_field(title,my_title)' < data.json

In the example above, we renamed all the title fields in the dataset into the my_title field.

One can also work on deeply nested data. E.g. create a deeply nested data structure with the move_field Fix command:

    $ catmandu convert JSON --fix 'move_field(title,my.deeply.nested.title)' < data.json

In this example we moved the field title into the field my, which contains a (sub)field deeply, which contains a (sub)field nested.

Catmandu was originally created by librarians for librarians. We process a lot of metadata especially library metadata in formats such as MARC, MAB2 and MODS. With the following command we can extract data from a marc record and to store it into the title field (requires Catmandu::MARC):

    $ catmandu convert MARC --fix 'marc_map(245,title)' < data.mrc

Or, in case only the 245a subfield is needed write:

    $ catmandu convert MARC --fix 'marc_map(245a,title)' < data.mrc

When processing data a lot of Fix commands could be required. It wouldn't be very practical to type them all on the command line. By creating a Fix script which contains all the fix commands complicated data transformations can be created. For instance, if the file myfixes.txt contains:


then they can be executed on a MARC file using this command:

    $ catmandu convert MARC --fix myfixes.txt < data.mrc

Fixes can also be turned into executable scripts by adding a bash 'shebang' line at the top. E.g. to harvest records from an OAI repository write this fix file:

     #!/usr/bin/env catmandu run
     do importer(OAI,url:"")

Run this (on Linux) by setting the executable bit:

     $ chmod 755 myfix.fix
     $ ./myfix.fix

To experiment with the Fix language you can also run the catmandu Fix interpreter in an interactive mode:

     $ catmandu run
     Catmandu 0.95 interactive mode
     Type: \h for the command history
     fix > add_field(hello,world)
     hello: world
     fix >

Catmandu contains many powerful fixes. Visit to get an overview what is possible.


For more information read our documentation pages and blog for a complete introduction and update into all Catmandu features.

In the winter of 2014 an Advent calendar tutorial was created to provide a day by day introduction into the UNIX command line and Catmandu:

If you need extra training, our developers regulary host workshops at library conferences and events:


There are several ways to get a working version of Catmandu on your computer.

For a quick and demo installation visit our blog where a VirtualBox image is available containing all the Catmandu modules, including ElasticSearch and MongoDB. A similarly easy method is using Docker: At librecat/catmandu a Docker image is provided with version tags for each release, latest for the latest release and dev for the latest development version. The image can be tried online in a Jupyter notebook via binder.

On our website we provide installation instructions for:

Ubuntu Server

Open Source

Catmandu software published at is free software without warranty, liabilities or support; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 or any later version. Every contributor is free to state her/his copyright.

Developers & Support

Catmandu has a very active international developer community. We welcome all feedback, bug reports and feature enhancement.

Join our mailing list to receive more information:

Are a developer and want to contribute to the project? Feel free to submit pull requests or create new Catmandu packages!


Catmandu is created in a cooperation with many developers world wide. Without them this project isn't possible. We would like to thank our core maintainer: Nicolas Steenlant and all contributors: Christian Pietsch, Dave Sherohman, Friedrich Summann, Jakob Voss, Johann Rolschewski, Jorgen Eriksson, Magnus Enger, Maria Hedberg, Mathias Loesch, Najko Jahn, Nicolas Franck, Patrick Hochstenbach, Petra Kohorst, Snorri Briem, Upasana Shukla and Vitali Peil.