Shell scripts commonly used ANSI escape codes for color output.
Following table shows Numbers representing colors in Escape Sequences.
| Color | Foreground | Background |
|---|
| Black | 30 | 40 |
| Red | 31 | 41 |
| Green | 32 | 42 |
| Yellow | 33 | 43 |
| Blue | 34 | 44 |
| Magenta | 35 | 45 |
| Cyan | 36 | 46 |
| White | 37 | 47 |
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 CODE | Meaning |
|---|
| 0 | Normal Characters |
| 1 | Bold Characters |
| 4 | Underlined Characters |
| 5 | Blinking Characters |
| 7 | Reverse 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 summarises these differences.
| Bold off | color | Bold on | color |
|---|
| 0;30 | Balck | 1;30 | Dark Gray |
| 0;31 | Red | 1;31 | Dark Red |
| 0;32 | Green | 1;32 | Dark Green |
| 0;33 | Brown | 1;33 | Yellow |
| 0;34 | Blue | 1;34 | Dark Blue |
| 0;35 | Magenta | 1;35 | Dark Magenta |
| 0;36 | Cyan | 1;30 | Dark Cyan |
| 0;37 | Light Gray | 1;30 | White |
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:
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.But it is
less flexible than ANSI escape sequences.
