Introduction
The echo command outputs a given string to the commonplace output pipe, sometimes pointing to the terminal. Though the usual output pipe can level to different interfaces – the echo command is often used to print and show messages within the terminal. By default, the textual content of the displayed messaged inherits the colour of different textual content within the terminal (which is customizable in and of itself). Nonetheless – there are a number of methods you may alter the output coloration of echo – each for particular person strings and for whole messages.
On this quick information, we’ll check out how one can change the output coloration of
echoin Linux-based programs, utilizing ANSI escape codes,tputand how one can make this course of much less verbose in Bash scripts.
Change Output Shade with ANSI Escape Codes
The simplest method to change the colour is thru ANSI escape sequences/codes. All ANSI escape codes begin with the Escape character, which may be represented in varied codecs – 27 in decimal, x1B in hexadecimal, because the management key ^[, or 33 in octal format. The sequences are then followed by the command:
33[command
Where the opening bracket (Control Sequence Introducer) is optional, but helps separate the command from the escape character. When you put a color code as the command, it changes the color of the oncoming text:
33[0;34
0;34 is the code for the color blue, for example. With this alone, you can change the color of text in echo with:
33[0;34Text
Where Text would be colored blue. Alternatively, consider a simple bash script to print “Welcome to France” in the colors of the French flag:
#!/bin/bash
BLUE=' 33[0;34m'
WHITE= ' 33[0;37m'
RED= ' 33[0;31m'
echo -e "${Blue}Welcome ${WHITE}to ${RED}France"
The optional -e flag of the echo command allows you to use special characters like n (newline) and t (tab) inside of the input string.
Once you run the script:
$ ./colors.sh
It results in:
The ANSI codes aren’t limited to color – but can also be applied for style. The codes 0..9 represent text styles, while the codes 30...37 represent colors:
| Color | Codes | Text Styles | Codes |
| Black | 30 | Simple text | 0 |
| Red | 31 | Bold text | 1 |
| Green | 32 | Low intensity text | 2 |
| Brown/Orange | 33 | Underline text | 4 |
| Blue | 34 | Blinking text | 5 |
| Purple | 35 | Invisible text | 8 |
| Cyan | 36 | Strikethrough text | 9 |
| Light Gray | 37 |
Let’s create a bash script to explore some of these options:
#!/bin/bash
echo -e " 33[0;33mSample text"
echo -e " 33[1;33mBold text"
echo -e " 33[2;33mLow intensity text"
echo -e " 33[4;33mUnderline text"
echo -e " 33[5;33mBlinking text"
echo -e " 33[8;33mInvisible text"
echo -e " 33[9;33mStrikethrough text"
Running this script results in:
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Similarly, you can change the background color of these texts using codes 40..47:
| color | Codes |
| Black | 40 |
| Red | 41 |
| Green | 42 |
| Brown/Orange | 43 |
| Blue | 44 |
| Purple | 45 |
| Cyan | 46 |
| Light Gray | 47 |
Changing the background of a given string boils down to the same rule as when changing the font color – the code itself changes the behavior:
#!/bin/bash
BLUE=' 33[0;44m'
BLACK=' 33[0;30m'
WHITE=' 33[0;30;47m'
RED=' 33[0;41m'
echo -e "${BLUE}Welcome ${WHITE}to ${RED}France"
Note: As a rule of thumb – you can translate font colors to background colors by adding 10. 30 is black font color, 40 is black background color.
Change the Output Color with the tput
An alternative to ANSI codes is using the tput command:
$ tput setaf color_code
setf allows for 8 colors, while setaf allows for 256 colors so depending on the command you’re using, you can go between 0..7 and 0..255 as the color codes. Both commands dedicate 0..7 to the same color codes, while with setaf, 8..15 are high-intensity colors, and 16..231 are different hues of the first 8, and 232..255 are greyscale colors:
Credit: Wikipedia
Finally, tput also allows you to change the background color, add bold, lower the intensity, etc. with other commands:
| Text Styles | Commands |
| Foreground color | setaf |
| Background color | setab |
| No style | sgv0 |
| Bold text | bold |
| Low-intensity text | dim |
| Underline text | smul |
| Blinking text | blink |
| Reverse text | rev |
Let’s create another script that uses tput to change the output color echo:
#!/bin/bash
YELLOW=`tput setaf 3`
echo "${YELLOW}Changing"
WHITE=`tput setaf 7 bold`
echo "${WHITE}Colors"
BLUE=`tput setaf 4 smul`
echo "${BLUE}With tput"
CYAN=`tput setaf 6 blink`
echo "${CYAN}is less"
RED=`tput setab 1 setaf 7`
echo "${RED}verbose!"
This script will print the following output in the terminal:
The tput command delivers an easy way to print any color through a simple color code. Let’s now create a script that can print every color code available for the tput command:
#!/bin/bash
tput init
end = $ (($ (tput colors) - 1))
w = 1
for c
in $ (seq 0 $end)
do
eval "$(printf " tput setaf % 3 s " " $c ")"
echo - n "$_"
[[$c - ge $ ((w * 2))]]
offset = 2 || offset = 0
[[$ (((c + offset) % (w - offset))) - eq $ (((w - offset) - 1))]]
echo
executed
tput init
It’s going to print 0 to 255 coloration and their codes:
Conclusion
On this quick information – we have taken a take a look at how one can change the colour of echo‘s output in Linux – utilizing ANSI Escape Sequences and the tput command.
We have additionally explored how one can make the method much less verbose utilizing Bash variables, tweak background colours and elegance textual content.
