Bash Colors: colorizing shell scripts

Bash Colors: colorizing shell scripts

Shell scripts commonly used ANSI escape codes for color output.

Following table shows Numbers representing colors in Escape Sequences.

ColorForegroundBackground
Black3040
Red3141
Green3242
Yellow3343
Blue3444
Magenta3545
Cyan3646
White3747

 

The numbers in the above table work for xterm terminal.Result may vary for other terminal emulators.

Use the following template for writing colored text. echo -e “\033[COLORm Sample text” The “\033[” begins the escape sequence.

You can also use “\e[” instead of “\033[“. COLOR specifies a foreground color, according to the table above.

The “m” terminates escape sequence, and text begins immediately after that.

Note: With an echo, the -e option enables the escape sequences.You can
also use printf instead of echo.

printf “\e[COLORm sample text\n” To print Green text echo -e “\033[32m Hello World” or printf “\e[32m Hello World”

The problem with above statement is that the blue color that starts with the 32 color code is never switched back to the regular color,so any text you type after the prompt and even prompt also is still in the Green color.

To return to the plain, normal mode, we have yet another sequence. echo -e “\033[0m” Now you won’t see anything new on the screen, as this echo statement was not passed any string to display.

But it has done its job, which was to restore the normal viewing mode.

Whatever yor type now will be avoid of any fancy effects.

Escape sequence also allow you to control the manner in which characters are displayed on the screen.

The following table summarizes numbers representing text attributes in Escape Sequences:

ANSI CODEMeaning
0Normal Characters
1Bold Characters
4Underlined Characters
5Blinking Characters
7Reverse video Characters

 

Note: Blink attribute doesn’t work in any terminal emulator, but it will work on the console. Combining all these Escape Sequences, you can get more fancy effect. Use the following template for writing colored text on a colored background. echo -e “\033[COLOR1;COLOR2m sample text\033[0m” The semicolon separated numbers “COLOR1” and “COLOR2″ specify a foreground and a background color.The order of the numbers does not matter, since the foreground and background numbers fall in non- overlapping ranges.”m” terminates the escape sequence, and the text begins immediately after that.Although setting the colors separately also work (i.e. \033[44m\033[32m). There are some differences between colors when combining colors with bold text attribute. The following table summarizes these differences.

colorBold oncolor
Balck1;30Dark Gray
Red1;31Dark Red
Green1;32Dark Green
Brown1;33Yellow
Blue1;34Dark Blue
Magenta1;35Dark Magenta
Cyan1;30Dark Cyan
Light Gray1;30White

Bold off
0;300;310;320;330;340;350;360;37

 

The following shell script prints all the colors and codes on the screen.

#!/bin/bash # This script echoes colors and codes echo -e “\n\033[4;31mLight Colors\033[0m \t\t\033[1;4;31mDark Colors\033[0m” echo -e “\e[0;30;47m Black \e[0m 0;30m \t\e[1;30;40m Dark Gray \e[0m 1;30m” echo -e “\e[0;31;47m Red \e[0m 0;31m \t\e[1;31;40m Dark Red \e[0m 1;31m” echo -e “\e[0;32;47m Green \e[0m 0;32m \t\e[1;32;40m Dark Green \e[0m 1;32m” echo -e “\e[0;33;47m Brown \e[0m 0;33m \t\e[1;33;40m Yellow \e[0m 1;33m” echo -e “\e[0;34;47m Blue \e[0m 0;34m \t\e[1;34;40m Dark Blue \e[0m 1;34m” echo -e “\e[0;35;47m Magenta \e[0m 0;35m \t\e[1;35;40m DarkMagenta\e[0m 1;35m” echo -e “\e[0;36;47m Cyan \e[0m 0;36m \t\e[1;36;40m Dark Cyan \e[0m 1;36m” echo -e “\e[0;37;47m LightGray\e[0m 0;37m \t\e[1;37;40m White \e[0m 1;37m”
OUTPUT:

bash colors

Some examples:

Block background and white text

echo -e “\033[40;37m Hello World\033[0m”

Reverse video text attribute option interchanges fg and bg colors.
Bellow statement prints block on white

echo -e “\033[40;37;7m Hello World\033[0m”

echo -e “\033[33;44m Yellow text on blue background\033[0m”
echo -e “\033[1;33;44m Bold yellow text on blue background\033[0m”
echo -e “\033[1;4;33;44mBold yellow underlined text on blue background\033[0m”

The “tput” command:

Other than echo there is a command called tput using which we
can control the way the output is displayed on the screen and control our bash colors.But it is
less flexible than ANSI escape sequences.

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