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Adding colors to Bash scripts

ifenna__ profile image Ifenna Updated on ・2 min read

I recently wrote a post-receive git hook for a server and I wanted to easily distinguish my hook's output from git information. This led me to look into colorizing bash output.

By using ANSI color escape codes, we can add color to output strings. The ANSI standard specifies certain color codes;

Color Foreground Code Background Code
Black 30 40
Red 31 41
Green 32 42
Yellow 33 43
Blue 34 44
Magenta 35 45
Cyan 36 46
Light Gray 37 47
Gray 90 100
Light Red 91 101
Light Green 92 102
Light Yellow 93 103
Light Blue 94 104
Light Magenta 95 105
Light Cyan 96 106
White 97 107

To change the color of the text, what we want is the foreground code. There are also a few other non-color special codes that are relevant to us:

Code Description
0 Reset/Normal
1 Bold text
2 Faint text
3 Italics
4 Underlined text

The echo command prints out text. We need to tell it that we're working with special ANSI codes, not just regular characters. This can be accomplished by adding a \e at the beginning to form an escape sequence. The escape sequence for specifying color codes is \e[COLORm (COLOR represents our color code in this case). By default, echo does not support escape sequences. We need to add the -e option to enable their interpretation.

To print red text, therefore, we could have

echo -e "\e[32mRed text\e[0m"

The \e[0m means we use the special code 0 to reset text color back to normal. Without this, all other text you print out after this would be red.

This works, but it would be more readable if we store the color codes in variables and use those instead.

RED="\e[31m"
ENDCOLOR="\e[0m"

echo -e "${RED}Red text${ENDCOLOR}"

Putting all these together, we could have a script like this

#! /usr/bin/env bash

RED="\e[31m"
GREEN="\e[32m"
ENDCOLOR="\e[0m"

echo -e "${RED}This is some red text, ${ENDCOLOR}"
echo -e "${GREEN}And this is some green text${ENDCOLOR}"

Demoing this

We can combine escape codes to get more fancy output.

#! /usr/bin/env bash

RED="31"
GREEN="32"
BOLDGREEN="\e[1;${GREEN}m"
ITALICRED="\e[3;${RED}m"
ENDCOLOR="\e[0m"

echo -e "${BOLDGREEN}Behold! Bold, green text.${ENDCOLOR}"
echo -e "${ITALICRED}Italian italics${ENDCOLOR}"

Another one

You can use these in any number of ways to make your scripts less monotonous. The combinations are up to you. Happy scripting!

Discussion

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Using escape codes directly is cool, but I'm a fan of using tput like this:

# SET Attribute Foreground <colour 123>
kindalightblue=$(tput setaf 123)

There are a lot of handy things tput can do, and though the capabilities vary with your terminal, and though it's not completely portable either, you get all the colours your terminal can show.

 

I haven't heard about tput before. I'll definitely check it out.

EDIT: Just took a look. It's great. Thanks for the tip 🚀.

 

If you want to see the colors you can use this script: gist.github.com/dtmilano/4055d6df5... which uses tput.

 

Thank you for the super helpful post.
I think the first example should be: echo -e "\e[31mRed text\e[0m"
32 represents green.

 

Awesome post, but you have a missing "m" in the first example:
echo -e "\e[32Red text\e[0m"
It should be:
echo -e "\e[32mRed text\e[0m"

 

Thanks for noticing! Fixed it.

 

Great article. Something that should be simple but is actually super hard to understand thank you