Syntax highlighting in pagers (eg. like less) using GNU source-highlight
Mar 21st, 2021 by miki

There is this nifty OS project, GNU, which has this nifty piece of software for syntax highlighting, source-highlight (aka. src-highlite), together with which is distributed this nifty shell script,, meant for piping arbitrary text through the highlighter selecting and applying a sensible highlight language definition, before being paged in some nifty pager which is able to interpret ANSI escape codes (ISO/IEC 6429 or ECMA-48, previously ANSI X3.64/FIPS PUB 86) like fx. the nifty and ubiquitous less.

Sadly, even after having installed less and source-highlight on modern Ubuntu and Debian systems they are not inter-operating by default. You’d have to feel the itch of syntax highlighting, discover source-highlight and dig its documentation to find out about said script.

TL;DR – quick and simple setup

Below is a quick two-line shell HOW-TO which sets up environment variables for the current user to enable auto-detection of language and subsequent syntax highlighting pr. default in less using GNU source-highlight (here done on Ubuntu 20.04 LTS, should behave similarly on Debian and derived distributions);

$ sudo apt install source-highlight
$ echo -e "\nexport LESSOPEN=\"| /usr/share/source-highlight/ %s\"\nexport LESS=' -R '" >> ~/.bash_aliases


This setup will make fx. some C source code display as below in less.

environment set up for less to enable ANSI color codes and pass any text through source-highlighter for potential ANSI escape code addition

less showing highlighted C code, auto-detected and highlighted by GNU source-highlighter

For the conservative

If you’d still like to have a “plain less” not messing with and amending you text, you could make an alias to use specifically when you want syntax highlighting. Put these somewhere interpreted by you shell (for bash fx. ~/.bash_aliases);

# syntax highligt in less
alias lesssh="LESSOPEN='|/usr/share/source-highlight/ %s' LESS=' -R ' less"
function lessurl() { wget -O- -q $1 |source-highlight -f esc -s html |less -R; }

Line two is a bonus shell function pulling some HTML from a webserver using wget, adding syntax highlighting and showing it in less.

Digging deeper

For the brave, take a tour of the “info source-highlight” (or “man source-highlight”) manuals (also here) to become familiar with the tool. You can use it anywhere you’d like some colour on arbitrary text and where color are supported in various ways and encodings, for example HTML and latex;

source-highlight adding color encoding to C code using HTML and latex encoding

If you are a programmer wanting to add highlighting features to you own application, the command line utilities are building on a highlighting library which you can utilise (API documentation here).

[Danish] Stallman til Danmark i Maj 2019!
Apr 7th, 2019 by miki

Update: Jeg mødte Richard i Odense, fik lov at sponsorere FSF og fik en GNU med hjem!

Mikkel & RMS (og GNU)
SDU, Odense

Rygterne har lydt noget tid, men nu er det officielt at formand for og stifter af Free Software Foundation, den ideologiske ophavsmand til GNU-projektet og højlydt fortaler for softwarebrugeres frihed og privatliv i den digitale verden, Richard Stallman besøger Danmark med en række åbne og gratis foredrag dette forår.

Det er Stallmans dedikerede arbejde med fri software og GNU-projektet fra starten af 1980’erne, herunder udformning af softwarelicenser som GNU GPL og udviklingsværktøjer som GNU Compiler Collection (GCC) og GNU Emacs, der er grundlaget for en stor del af det der i offentligheden i dag bedst kendes som “open source”. I Stallmans og GNUs terminologi benævnes det dog retteligt “fri software” (på engelsk: “free software”) for at fremhæve at etablering og bevarelse af softwarens, og slutbrugeren af dens, frihed er det egentlige rationale for at give kildekoden fri.

Kernen Linux er frigivet under GNU GPL og er både inspireret af og anvender GNU-projektets arbejde direkte, og er en vigtig del af et komplet GNU-system (også kendt som GNU/Linux eller en “Linux-distribution”).

Stallman kommer på en veritabel Danmarksturne med start i Aalborg mandag d. 6. maj 2019 og ender i København fredag d. 10.  maj 2019. Foredragsrækken er arrangeret af innovationsnetværket for IT, InfiniIT, som inkluderer de store IT-universiteter i Danmark.

Den samlede foredragsrække er som følger:

Tidspunkt Lokation Begivenhed hos FSF Begivenhed hos InfinIT Anden omtale
Mandag d. 6. maj 2019


Aalborg Universitet
Auditoriet, Lokale 1.12
Niels Jernes Vej 8A
9220 Aalborg SØVejviser:

Richard Stallman – “Free software and your freedom” Free Software, Free Society – Richard Stallman og den frie software-bevægelse (AAU)
Tirsdag d. 7. maj 2019


Syddansk Universitet
Lokale U170
Bygning 44
Campusvej 55
5230 OdenseVejviser:

Richard Stallman – “The dangers of mass surveillance” A Free Digital Society – Richard Stallman og den frie software-bevægelse
Onsdag d. 8. maj 2019


IT-Universitetet i København
Rued Langgaards Vej 7
2300 København SVejviser:

Richard Stallman – “Free software and your freedom in computing” A Free Digital Society – Richard Stallman og den frie software-bevægelse
Torsdag d. 9. maj 2019


Københavns Universitet
Københavns Biocenter
Lundbeckfond Auditorium Ole Maaløes Vej 5
2200 København NVejviser

Richard Stallman – “Computing, freedom, and privacy” Free Software, Free Society – Richard Stallman og den frie software-bevægelse (KU)
Fredag d. 10. maj 2019


Danmarks Tekniske Universitet
Auditorium 116/81 (bygning 116)
Ved Bygningstorvet på Knuth-Wintherfeldts Allé
2800 Kongens LyngbyVejviser:

Richard Stallman – “Copyright vs Community”

(ændrede lokationsoplysninger ikke opdaterede her)

Copyright vs Community Richard Stallman og den frie software-bevægelse

Kilder: FSF: Where in the world is Richard Stallman?, InfinIT-arrangementer, IDA-søgning, PROSA-arrangementer

Begivenhederne er også tilføjet den åbne kalender GriCal:

Information om Richard/GNU/FSF

De primære kilder er hovedsageligt på engelsk:

Kilder på dansk


Anden omtale

Stallman in 2012: Denmark supposedly a free country, still valid
Mar 3rd, 2017 by miki

Stumbled upon this slightly dated talk by Richard M. Stallman (aka. RMS) of GNU and FSF fame, in which my home country of Denmark is sadly referenced as only a “supposedly free country”.


“But censorship is wrong, of course, whether it is done on the internet or not. We used to think that the internet would protect us from censorship because it was too hard to censor the internet. But thanks to the efforts of various companies in the US, The UK, France and so on, it is now possible for governments to censor the internet and also surveil it completely, they just need to put enough effort in. And this is not limited to obvious tyrannies such as China and Iran. We see a lot of supposedly free countries imposing censorship on the internet.

For instance, Denmark several years ago imposed filtering on the internet blocking a secret list of sites. The list was leaked and posted on WikiLeaks. Hooray for WikiLeaks! Whereupon Denmark blocked access to that page too. So everyone else could know what internet users in Denmark were blocked from seeing except those people.”

Sadly since this time it has not gotten any better. Most of the points RMS makes (the whole talk is worth a listen) are still valid and a grave concern from my perspective. The Danish internet (really DNS) blocking system has been broadened and the slippage that was feared has become a reality. Even though this issue has gotten some attention in the IT and rights communities the general public just doesn’t care.

The actual block is technically done through DNS blacklists that Danish ISP are legally required to implement. The list of blocked sites is available from the telecom trade organization “Telekommunikationsindustrien i Danmark” (English: Telecommunication’s Industry Association in Denmark) at and currently has 111 sites (csv) on active block.

As it being DNS based if you are impacted, workarounds do exist. However, my guess is that they will soon be able to actively shut down services physically located in Denmark.

Full talk

Below are links to the full talk, and an inline/embedded player courtesey of youtube. Start time of all links are at starting point of above transcript.


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