Sed – the Stream EDitor

Posted on December 30, 2021November 14, 2024 by Marco Antonio Carcano

Sed is a command line tool that can really do amazing stream manipulations: despite it certainly being a "seasoned" tool, it is very likely that there are a lot of sed one-liners inside your Company's scripts.

Having at least an understanding of it is a must if you want to be able to maintain this legacy stuff that very often is not worth the effort to rework.

And anyway, when having to deal with quick and dirty solutions that rely on shell scripts, or when writing documentation with shell commands that can be easily replaced by a copy and paste by the reader... it's still an excellent tool honestly I cannot work without.

The aim of this post is to provide an easy tutorial to quickly learn how to use sed in every situation that can be easily sorted out with a sed one-liner.

In memory of Lee E. McMahon, contributor to early versions of the Unix operating system, ... and of course in particular of the sed stream editor.

Files: verifying checksums, comparing files and generating patches

Posted on December 13, 2021November 14, 2024 by Marco Antonio Carcano

Despite it is a boring task, comparing file is a need that sometimes IT professionals have to deal with: there are many reasons for having to deal with this:

verify if a file has been corrupted
verify if a file has been tampered
compare two versions of a configuration file to see where they differ - this happens quite often when after a configuration modification an application stops working as it should and you have to guess why
generate a patch that can be used to go back and forth to current and previous version of the same files

and so on.

This post explains how to deal with these needs on Linux using the tools provided by the Linux distribution.

YAML in a nutshell

Posted on November 21, 2021November 14, 2024 by Marco Antonio Carcano

YAML is a must-have skill for IT professionals, since it is probably becoming the the most commonly used document format for manifest and configuration files - think for example to Kubernetes, Ansible and a lot of other modern Dev-Ops oriented or CI/CD tools such as drone.

Being skilled on YAML does not only mean being able to write YAML documents, but also efficiently query and manipulate YAML files.

This post provides everything it is very likely you must know to exploit YAML in your daily work, explaining its syntax and showing things in action by using yq - a tool we can consider "the jq for YAML", and using Python with PyYAML.

By the way, this post is part of a trilogy of posts dedicated to markup and serialization formats, so be sure not to miss

JSON and jq in a nutshell

Posted on November 19, 2021November 14, 2024 by Marco Antonio Carcano

JSON is a must-have skill for IT professionals, since it is probably the most used document format when dealing with AJAX and with REST web-services: since both of them are broadly used on the web, it is very likely that sooner or later you'll ever have to deal with it.

Being skilled on JSON does not only mean being able to write JSON documents, but also knowing how to exploit tools such as jq to extract values or even a subset from a JSON document.

Having these skills makes your life easier not only if you are a developer, but also if you are involved in the system integration field.

This post is an overview about all you must know about JSON and how to work with it using jq.

By the way, this post is part of a trilogy of posts dedicated to markup and serialization formats, so be sure not to miss

XML in a nutshell

Posted on November 4, 2021November 14, 2024 by Marco Antonio Carcano

XML is a must-have skill for every professional: it is still broadly used by application protocols such as SOAP or SAML, or by description languages such as WSDL. By the way it is not something that is bound only to the application integration field: several applications relies on XML based configuration files and Blueprints, think for example to Apache Tomcat configuration files ("server.xml", "context.xml", ...), OSGI Blueprints such as a JAAS configuration, or again to Maven POM files or SCAP files (OVAL, XCCDF, ...).
The aim of this post is to provide a good overview of XML, explaining its goals, how to enforce it using schemas and generate a human-readable view of an XML file using XSLT.

The post also provides an overview of the XPath query language with some examples using the xpath command line tool. It shows you how to modify XML nodes and attributes using the xmlstarlet command line tool.

By the way, this post is part of a trilogy of posts dedicated to markup and serialization formats, so be sure not to miss

Of course these things would deserve a whole book, ... but as usual I try to be synthetic, showing you only the things that are really likely you'll sooner or later come across when working with XML, and giving tips on where to find more information on each topic.

Packaging a Python Wheel as RPM

Posted on October 31, 2021November 14, 2024 by Marco Antonio Carcano

This is the last post of the trilogy dedicated to how to set up a well structured Python project, developed with professional style, suitable to be used within the context of a Continuous Integration toolchain. This time we focus on how to package all we have done so far as RPM packages, showing how to break down everything into subpackages that also perform post installation tasks.
If you haven't read the previous two posts, you must do it right now since they are requisite to understand this post. In addition to that this post relies onto objects that are being created in the previous posts.

Read them in the following order:

The operating environment used in this post is Red Hat Enterprise Linux 8 or CentOS 8 - using a different environment may lead to having to adapt or even change things.