Colorize Terminal Text with Escape Sequences in Linux

ANSI escape codes can be used to style the output of echo or printf. An escape code is a sequence of characters start with an ESC character, followed by second character in the ASCII range 64 to 95. This sequence can be of different length.

The general format of escape code for styling the terminal text is:
ESC[{attr1};{attr2};....{attrn)m.

Note that above escape code sequece ends with m and there is no ; before that.

The ASCII equivalent of ESC character is 033(in decimal) or 0x1b(in hexa). We use 033 because it works for all operating systems.

Some examples for escape codes are:

'\033[0m'       #Reset text
'\033[0;33m'    #Yello color text
'\033[42m'      #Green background
'\033[1;42m'    #Bold text with Green background

If we examine the code '\033[1;42m',

\033	[	1	;	42	m
Octal value of `ESC` char.	left square bracket	Attribute 1 (bold)	Divider	Attribute 2 (Green)	Ending Char.

Usage with `echo`

$ echo -e '\033[1;42m'This is text with green background

Don’t forget to use -e option along with echo command. Any text following the above code sequence will print with green background color.

Usage with `printf`

$ printf '\033[1;42m'This is text with green background

Text Formatting

Examples of text formatting:

Value	Escape Code	Text Style
0	'\033[0;31m'	Regular
1	'\033[1;31m'	Bold
2	'\033[2;31m'	Low Intensity
3	'\033[3;31m'	Italic
4	'\033[4;31m'	Underline
5	'\033[5;31m'	Blinking
6	'\033[6;31m'	Reverse
7	'\033[7;31m'	Background
8	'\033[8;31m'	Invisible

Text Colour

Examples of text color:

Value	Escape Code	Text Color
30	'\033[0;30m'	Black
31	'\033[0;31m'	Red
32	'\033[0;32m'	Green
33	'\033[0;33m'	Yello
34	'\033[0;34m'	Blue
35	'\033[0;35m'	Magenta
36	'\033[0;36m'	Cyan
37	'\033[0;37m'	White

Background Colour

Examples of Background color:

Value	Escape Code	Background Color
40	'\033[0;40m'	Black
41	'\033[0;41m'	Red
42	'\033[0;42m'	Green
43	'\033[0;43m'	Yello
44	'\033[0;44m'	Blue
45	'\033[0;45m'	Magenta
46	'\033[0;46m'	Cyan
47	'\033[0;47m'	White

Random Text Style Attributes

One or more attributes can be clubbed together for more styling.

A simple color echo solution for shell scripts

Save the following code in a file, let’s say cecho.sh

cecho() {
	local code="\033["
	case "$1" in
		black  | bk) color="${code}0;30m";;
		red    |  r) color="${code}1;31m";;
		green  |  g) color="${code}1;32m";;
		yellow |  y) color="${code}1;33m";;
		blue   |  b) color="${code}1;34m";;
		purple |  p) color="${code}1;35m";;
		cyan   |  c) color="${code}1;36m";;
		gray   | gr) color="${code}0;37m";;
		*) local text="$1"
			esac
			[ -z "$text" ] && local text="$color$2${code}0m"
			echo -e "$text"
}

Including the above file in any shell script will allow us to print color text on terminal.

Let’s say file display.sh has the following content.

#!/bin/sh
. /path/to/cecho.sh

cecho red "This is red text"

Now executing second shell script will display output in red color.

$ bash display.sh

color text on terminal using shell script

References

bash:tip_colors_and_formatting

Stackoverflow: Change echo output

Terminal color escape sequences

Usage with echo

Usage with printf