34.5. "Colorizing" Scripts
The ANSI [1] escape sequences set screen attributes, such as bold text, and color of foreground and background. DOS batch files commonly used ANSI escape codes for color output, and so can Bash scripts.
Example 34-8. A "colorized" address database
#!/bin/bash
# ex30a.sh: "Colorized" version of ex30.sh.
# Crude address database
clear # Clear the screen.
echo -n " "
echo -e '\E[37;44m'"\033[1mContact List\033[0m"
# White on blue background
echo; echo
echo -e "\033[1mChoose one of the following persons:\033[0m"
# Bold
tput sgr0
echo "(Enter only the first letter of name.)"
echo
echo -en '\E[47;34m'"\033[1mE\033[0m" # Blue
tput sgr0 # Reset colors to "normal."
echo "vans, Roland" # "[E]vans, Roland"
echo -en '\E[47;35m'"\033[1mJ\033[0m" # Magenta
tput sgr0
echo "ones, Mildred"
echo -en '\E[47;32m'"\033[1mS\033[0m" # Green
tput sgr0
echo "mith, Julie"
echo -en '\E[47;31m'"\033[1mZ\033[0m" # Red
tput sgr0
echo "ane, Morris"
echo
read person
case "$person" in
# Note variable is quoted.
"E" | "e" )
# Accept upper or lowercase input.
echo
echo "Roland Evans"
echo "4321 Floppy Dr."
echo "Hardscrabble, CO 80753"
echo "(303) 734-9874"
echo "(303) 734-9892 fax"
echo "revans@zzy.net"
echo "Business partner & old friend"
;;
"J" | "j" )
echo
echo "Mildred Jones"
echo "249 E. 7th St., Apt. 19"
echo "New York, NY 10009"
echo "(212) 533-2814"
echo "(212) 533-9972 fax"
echo "milliej@loisaida.com"
echo "Girlfriend"
echo "Birthday: Feb. 11"
;;
# Add info for Smith & Zane later.
* )
# Default option.
# Empty input (hitting RETURN) fits here, too.
echo
echo "Not yet in database."
;;
esac
tput sgr0 # Reset colors to "normal."
echo
exit 0 |
The simplest, and perhaps most useful ANSI escape sequence is bold text, \033[1m ... \033[0m. The \033 represents an escape, the "[1" turns on the bold attribute, while the "[0" switches it off. The "m" terminates each term of the escape sequence.
bash$ echo -e "\033[1mThis is bold text.\033[0m" |
A similar escape sequence switches on the underline attribute (on an rxvt and and an aterm).
bash$ echo -e "\033[4mThis is underlined text.\033[0m" |
 | With an echo, the -e option enables the escape sequences. |
Other escape sequences change the text and/or background color.
bash$ echo -e '\E[34;47mThis prints in blue.'; tput sgr0 bash$ echo -e '\E[33;44m'"yellow text on blue background"; tput sgr0 |
Use the following template for writing colored text on a colored background. echo -e '\E[COLOR1;COLOR2mSome text goes here.' The "\E[" begins the escape sequence. The semicolon-separated numbers "COLOR1" and "COLOR2" specify a foreground and a background color, according to the table below. (The order of the numbers does not matter, since the foreground and background numbers fall in non-overlapping ranges.) The "m" terminates the escape sequence, and the text begins immediately after that. Note also that single quotes enclose the remainder of the command sequence following the echo -e. |
The numbers in the following table work for an rxvt terminal. Results may vary for other terminal emulators.
Table 34-1. 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 |
Example 34-9. Echoing colored text
#!/bin/bash
# color-echo.sh: Echoing text messages in color.
# Modify this script for your own purposes.
# It's easier than hand-coding color.
black='\E[30;47m'
red='\E[31;47m'
green='\E[32;47m'
yellow='\E[33;47m'
blue='\E[34;47m'
magenta='\E[35;47m'
cyan='\E[36;47m'
white='\E[37;47m'
alias Reset="tput sgr0" # Reset text attributes to normal
#+ without clearing screen.
cecho () # Color-echo.
# Argument $1 = message
# Argument $2 = color
{
local default_msg="No message passed."
# Doesn't really need to be a local variable.
message=${1:-$default_msg} # Defaults to default message.
color=${2:-$black} # Defaults to black, if not specified.
echo -e "$color"
echo "$message"
Reset # Reset to normal.
return
}
# Now, let's try it out.
# ----------------------------------------------------
cecho "Feeling blue..." $blue
cecho "Magenta looks more like purple." $magenta
cecho "Green with envy." $green
cecho "Seeing red?" $red
cecho "Cyan, more familiarly known as aqua." $cyan
cecho "No color passed (defaults to black)."
# Missing $color argument.
cecho "\"Empty\" color passed (defaults to black)." ""
# Empty $color argument.
cecho
# Missing $message and $color arguments.
cecho "" ""
# Empty $message and $color arguments.
# ----------------------------------------------------
echo
exit 0
# Exercises:
# ---------
# 1) Add the "bold" attribute to the 'cecho ()' function.
# 2) Add options for colored backgrounds. |
 | There is, however, a major problem with all this. ANSI escape sequences are emphatically non-portable. What works fine on some terminal emulators (or the console) may work differently, or not at all, on others. A "colorized" script that looks stunning on the script author's machine may produce unreadable output on someone else's. This greatly compromises the usefulness of "colorizing" scripts, and possibly relegates this technique to the status of a gimmick or even a "toy". |
Moshe Jacobson's color utility (http://runslinux.net/projects/color) considerably simplifies using ANSI escape sequences. It substitutes a clean and logical syntax for the clumsy constructs just discussed.