modifying x resources on the fly
For these tricks, I am going to assume that you are using a somewhat sane terminal emulator. Everything I write about here works in xterm and urxvt, and most things should work in any vte-based terminal (gnome-terminal, termite, lxterminal etc).
Some things might or might not work in iTerm…
All things listed here does work in both GNU Screen and Tmux, but you will have to escape the escape sequences. ;)
Here’s a gif to keep you interested:
Changing terminal color schemes
If you for some reason wish to change the colorscheme in your terminal, this is the usual way to do so:
vim ~/.Xresources
<tedious edit>
<save>
xrdb !$
<close terminal session>
<start a new one>This gets old quickly, especially if you’re in the process of trying new colors out, not sure what you’ll end up with.
Most people are aware of the fact that you can modify some colors of your terminal, i.e the so called ANSI colors; color index 0-15. The colors are usualy set during xinit, like so:
~/.xinitrc:
xrdb ${XDG_CONFIG_HOME}/Xresources
Xresources:
.color0: #1b1d1e
.color1: #1b1d1e
...
.color15: #f8f8f2
.color16: #000000
When you log in to your system and start your first terminal, these colors will be set… in stone.
No, not really.
Let’s start two terminals, side by side: [IMAGE]
In both terminals, run this command:
for i in {0..15}; do printf "\e[48;5;${x}m%.2d\e[m\n" $i; done[IMAGE]
What you see is the currently defined ANSI color table. Now, in one of the terminals, run this:
for i in {0..15}; do printf "\e]4;$x;rgb:ff/00/00\e\\"; done[IMAGE]
We’ve just changed all of the defined ANSI colors to #ff0000, also known as ‘very red’, but only in the currently running terminal session. Not very useful, but bare with me.
Over the years I’ve stumbled upon countless open source projects that deal with terminal colors in any way that hardcode the color values. It seems to be a little known fact that the extended colorset is not only customizable, but you can modify them on the fly as well. Needless to say, hardcoded values are never good.
Let’s try to modify some non-ANSI colors, shall we?
for i in {17..33}; do printf "\e]4;$i;rgb:00/00/00\e\\"; done
If this doesn’t work for you and you’re using xterm, you might need to set these options in your Xresources configuration:
XTerm*dynamicColors: 1
XTerm*allowColorOps: 1
If you’re using urxvt and it doesn’t work, you might need to patch it.
So, we can modify colors, that’s great. But what about the hardcoded values we talked about earlier? If we modify our colors like crazy, the software that relies on those hardcoded default will break?
Well, they are broken to begin with, and they need to be fixed. We can query the terminal for the actual colors:
printf "\e]4;197;?\a"Output:
rgb:ffff/0000/5f5f
Color index 197 has the value of ff005f (default).
Let’s change its value and query the terminal again:
printf "\e]4;197;rgb:ff/ff/00\e\\"
printf "\e]4;197;?\a"Output:
rgb:ffff/ffff/0000
Pink turned yellow.
Maybe we can get away with assuming the first 16 ANSI colors are set to something somewhat sane, but applications that deal with these extended colors should either:
- Do the right thing and query the terminal for set colors.
- Explicitly state that it assumes that no colors are modified; i.e; default xterm colors.
Other escapes
The development of new terminal features has been pretty sparse over the past 27 years (ECMA-48, 1991).
And for good reasons. Having a standard is crucial for developers and users alike. Nowadays when talking about standards, the phrase ‘xterm compatible’ is common. Terminals claim to emulate most of xterm, when in reality they emulate the most commonly used control sequences.
There has been new development in this area though as of lately. A few new terminals that market themselves as using opengl to render the screen have seen the light, most notably kitty (not to be confused with the putty fork of the same name).
Resources
Term::ExtendedColor - Perl library for using extended colors in your terminal
Colorcoke - Program for changing the terminal colors in many ways
rgbterm - query the terminal for rgb values of defined terminal colors