How to show all colors supported by bash?

Question

One day, I typed the command

echo "\033[32mHELLOBASE\033[m"

in the gnome bash shell. The terminal showed me a green HELLOBASH string. I found this interesting. From my experience and serveral tests, I can change the number 32 from 0 up to 47. Next I wrote the following code,

for i in {0..48};do
    echo \033[$imHELLOBASH\[033m
done

Of course, it doesn't work, or I cannot be here! So how to improve the above code to function?

Nimitz

Bash doesn't natively show colors at all -- your terminal does that. If you want to look up what your terminal can and can't support, the tput command looks up the right codes for colors. – Cuprite

...the code you're using right now only works on some terminals -- on others, those codes would be garbage. Using tput means you always have the right code for the terminal type you're currently using. – Cuprite

...see mywiki.wooledge.org/BashFAQ/037 – Cuprite

Answer 1

Let's do this the right way -- looking up color codes in our termcap (or, for modern systems, terminfo) database using the tput command:

for ((i=0; i<=48; i++)); do
  tput setaf "$i"
  echo HELLOBASH
done

If you want to see all available colors on a 256-color terminal, use this code token from BashFAQ #37:

colors256() {
        local c i j

        printf "Standard 16 colors\n"
        for ((c = 0; c < 17; c++)); do
                printf "|%s%3d%s" "$(tput setaf "$c")" "$c" "$(tput sgr0)"
        done
        printf "|\n\n"

        printf "Colors 16 to 231 for 256 colors\n"
        for ((c = 16, i = j = 0; c < 232; c++, i++)); do
                printf "|"
                ((i > 5 && (i = 0, ++j))) && printf " |"
                ((j > 5 && (j = 0, 1)))   && printf "\b \n|"
                printf "%s%3d%s" "$(tput setaf "$c")" "$c" "$(tput sgr0)"
        done
        printf "|\n\n"

        printf "Greyscale 232 to 255 for 256 colors\n"
        for ((; c < 256; c++)); do
                printf "|%s%3d%s" "$(tput setaf "$c")" "$c" "$(tput sgr0)"
        done
        printf "|\n"
}
colors256

For additional background on how and why any of this works, see the bash-hackers page on terminal codes.

---

As for why your original code didn't work even on terminals using ANSI color codes, by the way -- @rici pegged it correctly: Your parameter expansion was ambiguous without adding curly braces.

That is to say:

$imHELLOBASH

...needed to be...

${i}mHELLOBASH

...to avoid the shell trying to find and expand a variable called imHELLOBASH rather than a variable named i.

Cuprite

termcap or terminfo? I think that is implementation dependant. – Colb

Depends on how modern your system is. These days, yes, it would be terminfo. – Cuprite

I thought termcap died out in the late 1980s, my recollection of the days of curses is a little shaky. Where the heck did you dig-up that program from? I'll bet you had to blow a lot of dust off it :-) – Colb

They were both being distributed when I started in the mid 90s. – Cuprite

Answer 2

It is not much to do with bash, more to do with the terminal driver. Rather than trying to use control characters, I suggest you use tput instead, for example:

i=1
while (( $i < 10 ))
do
    tput setaf $i
    echo "This is $i"
   (( i++ ))
done

Colb

Answer 3

A simple version of your loop might look something like this:

for i in {0..48}; do
  echo "$(tput setaf $i)HELLOBASH$(tput sgr0)"
done

If you prefer to use ANSI color codes rather than spawn a subshell to call tput, then you could go this way:

for i in {0..48}; do
  echo $'\E[38;5;'$i'm'HELLOBASH$'\E[00m'
done

If you want something more readable, you can use variables:

for i in {0..48}; do
  fg=$'\E[38;5;'$i'm'
  reset=$'\E[00m'
  echo "${fg}HELLOBASH${reset}"
done

Powerlevel10k has a handy one-liner for Zsh users to see a colormap.

I use a modified version of that in Bash and it works great. The only overly clever bit in this snippet is the first 16 colors are special. They take up 8 per line because it looks nicer to line them up that way, and then after that the color sequences need to go in a 6-per line gradient, so there's a bit of modulo/echo magic to make that happen.

function colormap() {
  local i bg fg reset
  reset=$'\E[00m'
  for i in {0..255}; do
    fg=$'\E[38;5;'$i'm'
    bg=$'\E[48;5;'$i'm'
    printf "%s  %s"    "$bg" "$reset"
    printf "%s%03d%s " "$fg" "$i" "$reset"
    (( i <= 15 && (i + 1)  % 8 == 0 )) && echo
    (( i > 15  && (i - 15) % 6 == 0 )) && echo
  done
}

The advantage of this is that it's simple, and way faster than making 256 calls to tput.

Burget