Seasoned Linux professionals thoroughly know data formats: it is mandatory since these formats are used by many tools as:

  • output format (CSV, XML, JSON, …)
  • the format for their settings files (YAML, TOML, XML, JSON, INI, …)
  • the format of the document to be sent to an API (XML by SOAP, JSON by REST)

It is straightforward that is mandatory to be familiar to Regular Expressions: many legacy tools like grep (in all of its flavours, such as egrep) and sed use them as pattern matching criteria. They should also know how to leverage on awk when a little bit of business logic is needed while processing data, and of course know most of the so called “coreutils” (sort, cut, wc, uniq, …). Modern Linux professionals are also skilled on format specific tools such as xpath and xmlstarlet (XML), jq (JSON) or yq (YAML).

In addition to that, Linux professionals should also have a thorough understanding of:

  • encryption technologies that guarantee data integrity and confidentiality on the disk (openssl, GPG, PGP, …)
  • encryption technologies that guarantee data integrity and confidentiality on the wire (TLS, X.509 certificates, Public Key Infrastructure
  • design patterns that exploit encryption technologies, such as Shamir’s Secret Sharing
  • Cryptographic API, such as PKCS#11

Honestly, in my experience, I saw too many technicians neglecting this topic, but believe me, this can be very dangerous.


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.

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Skilled professionals nowadays, besides being skilled on technical matters, are supposed to know how to operate according to the principles of modern product management methodologies such as Agile and Lean. The traditional waterfall approach of gathering all the requirements, design everything as a whole, develop everything and test everything before deploying has been superseded since it cannot bear the demand of a quick time to the market of modern times: it is very likely that the delivery comes too late, when the service is no-more needed. The aim of this post is to explain what you should know about  Agile and Lean methodologies so as to operate into teams that use them.

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When it comes to guarantee data confidentiality on the wire or on the disk we cannot be exempt to know how to use cryptography: this post provides a quick guide of both symmetric and asymmetric cryptography along with an overview of their bricks: RSA and DSA keys, Elliptic Curves keys, PGP Keys, Message Digest, HMAC, digital signature and encipherment. The aim is to provide the necessary terms and concepts to understand how to operate with cryptographic tools, providing examples with openssl.

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Don’t be tempted to skip this post: you would miss something valuable. Of course most of us know how to operate a filesystem, but the underlying details of POSIX filesystems are not broadly known by most of the people. In this post I describe them quite accurately, trying to keep at a level that may intrigue, but avoiding to be too theoretical. Having such an expertise is certainly one of the things that make the difference from a technician and a skilled professional. In addition to that, this skill may really save your life when facing weird things that sometimes may arise.

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A pillar every Linux professional must have are certainly Regular Expressions: they are broadly used every time is required to lookup or substitute a pattern that matches some criteria. Tools such as grep and sed miss almost all of their power if who is using them does not have a good understanding of Regular Expressions. This is really a huge topic: there's more than one book that is fully focused on regular expressions - this post is only a quick guide: the aim of this post is to let the reader get the gist of what Regular Expressions are by explaining everything that is needed to know to face the common use cases that may arise during daily work..

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