Print true color (24-bit) test pattern

Question

How can I test that my terminal / tmux is correctly setup to display truecolor / 24-bit color / 16.8 million colours?

Answer 1

The following script will produce a test pattern like:

You can optionally call it as:

width=1000 truecolor-test

and it will print a pattern of width columns.

#!/bin/bash
# Based on: https://gist.github.com/XVilka/8346728

awk -v term_cols="${width:-$(tput cols || echo 80)}" 'BEGIN{
    s="/\\";
    for (colnum = 0; colnum<term_cols; colnum++) {
        r = 255-(colnum*255/term_cols);
        g = (colnum*510/term_cols);
        b = (colnum*255/term_cols);
        if (g>255) g = 510-g;
        printf "\033[48;2;%d;%d;%dm", r,g,b;
        printf "\033[38;2;%d;%d;%dm", 255-r,255-g,255-b;
        printf "%s\033[0m", substr(s,colnum%2+1,1);
    }
    printf "\n";
}'

Answer 2

I edited the function from Tom Hale's answer here to add a option for the amount of lines, which splits up the output. I find it useful as it shows more detailed color.

#!/bin/bash
# Based on: https://gist.github.com/XVilka/8346728 and https://unix.stackexchange.com/a/404415/395213

awk -v term_cols="${width:-$(tput cols || echo 80)}" -v term_lines="${height:-1}" 'BEGIN{
    s="/\\";
    total_cols=term_cols*term_lines;
    for (colnum = 0; colnum<total_cols; colnum++) {
        r = 255-(colnum*255/total_cols);
        g = (colnum*510/total_cols);
        b = (colnum*255/total_cols);
        if (g>255) g = 510-g;
        printf "\033[48;2;%d;%d;%dm", r,g,b;
        printf "\033[38;2;%d;%d;%dm", 255-r,255-g,255-b;
        printf "%s\033[0m", substr(s,colnum%2+1,1);
        if (colnum%term_cols==term_cols) printf "\n";
    }
    printf "\n";
}'