Sergey Potapov

A word from rustacean, rubist and linuxoid.

Powering Less to Highlight Syntax and Display Line Numbers

Since I am a command line guy I use less tool everywhere and everytime to quickly take a look at files. And quite often those files are different scripts and source code. So, it would be great if syntax was highlighted automatically when I open a file with less. And probably it would be great as well if I saw line numbers.

Making less highlight syntax

It didn’t take a long time to find a solution. There is a pretty tool called source-highlight.

It might be exist in standard repository of your system. In Debian like Linux distribution(Debian, Ubuntu, Mint, etc) you can install it with command:

apt-get install source-highlight

It supports a realy big list of languages(in my case 143) and 12 output formats(esc, html, javadoc, latex, etc). You can use man to get closer with it:

man source-highlight

source-highlight package provides a little script which receives a source code file and prints highlighted code. Its path is /usr/share/source-highlight/ So we’re gonna to use it with less.

Fortunately _less is require flexible tool and we can customize it with number of invironment variables. One of them is LESSOPEN. A quote from man less:

    Command line to invoke the (optional) input-preprocessor.

So we can you any pipes to prepare an input for less.

Another variable we are going to use is LESS:

    Options which are passed to less automatically.

We will use -R option to allow ANSI colors.

So just set up this to variables:

export LESSOPEN="| /usr/share/source-highlight/ %s"
export LESS=' -R '

Making less display line numbers

To display line numbers just use -N option. If you want less to use it everytime add it to LESS variable as well:

export LESS=' -RN '

Make it work everytime

To make it work in all shell session just add the next code to the end of you $HOME/.bashrc file:

# syntax highlight for less
export LESSOPEN="| /usr/share/source-highlight/ %s"
export LESS=' -R -N'

Hope this was useful for you. Don’t be shy and leave you comments.