Thursday, September 11, 2014

Change the Colour of Emacs Shell Prompt and Font Highlighting

The project I'm currently working on is Linux based, and I just can’t get my head around vi no matter how hard I try. Fortunately I have root privileges, so Emacs to the rescue :)

We are using CentOS so installing is as easy as

 sudo yum install emacs   

One of the many reasons I really like Emacs is you can run a shell inside Emacs.
Press Alt – x
Type shell
Press enter
NB the Alt key in Emacs is often called the Meta key and the key combination above would be shortened to M – x

This allows me to split the Emacs window and have the shell in the bottom half and what I working on in the top half, see the image below. To switch between the shell and what I’m working on I press M – O (that’s Alt and the letter O and not the number zero, Alt zero will unsplit the screen)

If like me you’re running Emacs inside Putty the first thing you might notice is the shell prompt is in dark blue on a black background. Not only is this very difficult to read but it can cause eye strain making for an unpleasant work day.

To change the colour of the shell prompt, and any font highlighting in Emacs is actually very easy if you know how. However the settings are a bit hidden, here is how to change the colours of any text in Emacs.

First you need to find out the supported colours for your version of Emacs. I’m using an old version and it doesn't support many colours, see the image below. Newer versions of Emacs support many more colours. To list the colours do the following.
Press M – x
Type list-colors-display
Press enter

Make a note of the easy to read colours. Then to change the colour of the shell prompt inside Emacs
Press M – x
Type list-faces-display
Press enter
This will display all the Font Highlighting options you can change, see the image below. On the left you will see underlined text of the name of the setting. On the right you will see the current colour settings.

Find the text comint-highlight-prompt and move the cursor directly over the top of it and press the enter key (sometimes the comint-highlight-prompt option doesn't show up, I don’t know why). This will take you into another screen, see the image below.  

  1. If the square brackets on the left of “Foreground” don’t have an X inside them like circle 1 in the image above, move the cursor in between the square brackets and press enter. This will enable the Foreground option
  2. Now move the cursor directly on top of the current colour of the foreground, circle 2 in the image above
  3. Press enter
  4. Type in the new colour you would like for the shell prompt, circle 3 in the image above. I chose green so I could feel like I was using a 1980s terminal :)
  5. Press enter 
  6. Move the cursor to the “Save for future sessions”, circle 4 in the image above 
  7. Press enter 
  8. Press Ctrl – x k to close the current screen / buffer. 
And you’re done :) The shell prompt will be what every colour you set it to.
While you are at it I would recommend changing at least minibuffer-prompt as well, you will be reading the text displayed in the minibuffer-prompt a lot. If you are feeling up to it change all the other text colours you find hard to read using the process above.

If all else fails add the following to your .emacs file

  '(comint-highlight-prompt ((t (:foreground "green"))))  
  '(minibuffer-prompt ((t (:foreground "green"))))  

finally no matter which method you use to change the colour of the shell prompt in enacs, don't forget to back up your .emacs file. Recreating it takes far to long