I'm trying to practice code and integrating my other interests with it, and a strong interest of mine is genetics/science in general. I'm making a simple script to generate a random string, but if I use the input for a genetic code (AGCT), the cat output will be colored according to the letters (A - blue, G - green, C - red, T - yellow). I was scratching my head for a while on it, and my google-fu isn't very good. An output from the command (using the genetic code input) looks like this:

user@conroe$ random AGCT 128

And this is the code:

if [ $# == 2 ]
    { cat /dev/urandom | env LC_CTYPE=C tr -dc $1 | head -c $2; echo; }
        printf "${RED}error: ${NC}insufficient input\n"

Any help?

  • You can just pipe to sed as: random AGCT 128 | sed "s/A/${BLUE}A${NC}/" | sed "s/G/${GREEN}G${NC}/" and so on ...
    – Bichoy
    Jun 17, 2015 at 4:29
  • I'm not sure if I understand what you want to do. You want to color the output to the letter A with blue, G with green and so on?
    – VaTo
    Jun 17, 2015 at 4:56
  • @SaulOrtega Yep! Jun 17, 2015 at 5:01
  • Why the superfluous cat? You should just do < /dev/urandom env LC_TYPE=C tr -dc $1 | ....
    – Anthon
    Jun 17, 2015 at 5:52

1 Answer 1


You can pipe the output of < /dev/urandom tr -dc $1 | head -c $2 (I took the liberty of removing the UUOC and the apparently unneeded env LC_CTYPE=C and echo; you can restore them in your version however) to a while loop reading one character at the time and echoing different color escape sequences followed by a different character based on the read character:


if [ $# == 2 ]
    < /dev/urandom tr -dc $1 | head -c $2 | while read -n 1 x
        case $x in
                echo -ne '\033[0;34mA'
                echo -ne '\033[0;32mG'
                echo -ne '\033[0;31mC'
                echo -ne '\033[0;33mT'
    echo -e '\033[0m'
    exit 0
exit 1


  • 1
    Don't hardcode escape sequences, use tput which gets them from the current terminal definition: tput setaf 4; echo -n A, tput setaf 2; echo -n G, etc...
    – Celada
    Jun 17, 2015 at 5:27
  • It works, but I was looking for something that was only in one line. This splits it up and prints a new character each line. Jun 17, 2015 at 5:29
  • @ViktorAhlström This prints everything in only one line followed by a single newline at the end. Are you sure you copied the script exactly like it is? Also it's meant to be run in bash. Which shell are you using?
    – kos
    Jun 17, 2015 at 5:34
  • I'm using zsh, oops. Jun 17, 2015 at 5:40
  • 1
    @Celada It's more complicated that that. On OpenBSD: tput setaf 3 - tput: not enough arguments (3) for capability `setaf'; echo $TERM - xterm-256color; infocmp -1 | grep setaf - setaf=\E[%?%p1%{8}%<%t3%p1%d%e%p1%{16}%<%t9%p1%{8}%-%d%e38;5;%p1%d%;m,
    – lcd047
    Jun 17, 2015 at 5:49

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