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 34-9. A "colorized" address database

   1 #!/bin/bash
   2 # ex30a.sh: "Colorized" version of ex30.sh.
   3 #            Crude address database
   4 
   5 
   6 clear                                   # Clear the screen.
   7 
   8 echo -n "          "
   9 echo -e '\E[37;44m'"\033[1mContact List\033[0m"
  10                                         # White on blue background
  11 echo; echo
  12 echo -e "\033[1mChoose one of the following persons:\033[0m"
  13                                         # Bold
  14 tput sgr0
  15 echo "(Enter only the first letter of name.)"
  16 echo
  17 echo -en '\E[47;34m'"\033[1mE\033[0m"   # Blue
  18 tput sgr0                               # Reset colors to "normal."
  19 echo "vans, Roland"                     # "[E]vans, Roland"
  20 echo -en '\E[47;35m'"\033[1mJ\033[0m"   # Magenta
  21 tput sgr0
  22 echo "ones, Mildred"
  23 echo -en '\E[47;32m'"\033[1mS\033[0m"   # Green
  24 tput sgr0
  25 echo "mith, Julie"
  26 echo -en '\E[47;31m'"\033[1mZ\033[0m"   # Red
  27 tput sgr0
  28 echo "ane, Morris"
  29 echo
  30 
  31 read person
  32 
  33 case "$person" in
  34 # Note variable is quoted.
  35 
  36   "E" | "e" )
  37   # Accept upper or lowercase input.
  38   echo
  39   echo "Roland Evans"
  40   echo "4321 Floppy Dr."
  41   echo "Hardscrabble, CO 80753"
  42   echo "(303) 734-9874"
  43   echo "(303) 734-9892 fax"
  44   echo "revans@zzy.net"
  45   echo "Business partner & old friend"
  46   ;;
  47 
  48   "J" | "j" )
  49   echo
  50   echo "Mildred Jones"
  51   echo "249 E. 7th St., Apt. 19"
  52   echo "New York, NY 10009"
  53   echo "(212) 533-2814"
  54   echo "(212) 533-9972 fax"
  55   echo "milliej@loisaida.com"
  56   echo "Girlfriend"
  57   echo "Birthday: Feb. 11"
  58   ;;
  59 
  60 # Add info for Smith & Zane later.
  61 
  62           * )
  63    # Default option.	  
  64    # Empty input (hitting RETURN) fits here, too.
  65    echo
  66    echo "Not yet in database."
  67   ;;
  68 
  69 esac
  70 
  71 tput sgr0                               # Reset colors to "normal."
  72 
  73 echo
  74 
  75 exit 0


Example 34-10. Drawing a box

   1 #!/bin/bash
   2 # Draw-box.sh: Drawing a box using ASCII characters.
   3 
   4 # Script by Stefano Palmeri, with minor editing by document author.
   5 # Used in the "ABS Guide" with permission.
   6 
   7 
   8 ######################################################################
   9 ###  draw_box function doc  ###
  10 
  11 #  The "draw_box" function lets the user
  12 #+ draw a box into a terminal.       
  13 #
  14 #  Usage: draw_box ROW COLUMN HEIGHT WIDTH [COLOR] 
  15 #  ROW and COLUMN represent the position        
  16 #+ of the upper left angle of the box you're going to draw.
  17 #  ROW and COLUMN must be greater than 0
  18 #+ and less than current terminal dimension.
  19 #  HEIGHT is the number of rows of the box, and must be > 0. 
  20 #  HEIGHT + ROW must be <= than current terminal height. 
  21 #  WIDTH is the number of columns of the box and must be > 0.
  22 #  WIDTH + COLUMN must be <= than current terminal width.
  23 #
  24 # E.g.: If your terminal dimension is 20x80,
  25 #  draw_box 2 3 10 45 is good
  26 #  draw_box 2 3 19 45 has bad HEIGHT value (19+2 > 20)
  27 #  draw_box 2 3 18 78 has bad WIDTH value (78+3 > 80)
  28 #
  29 #  COLOR is the color of the box frame.
  30 #  This is the 5th argument and is optional.
  31 #  0=black 1=red 2=green 3=tan 4=blue 5=purple 6=cyan 7=white.
  32 #  If you pass the function bad arguments,
  33 #+ it will just exit with code 65,
  34 #+ and no messages will be printed on stderr.
  35 #
  36 #  Clear the terminal before you start to draw a box.
  37 #  The clear command is not contained within the function.
  38 #  This allows the user to draw multiple boxes, even overlapping ones.
  39 
  40 ###  end of draw_box function doc  ### 
  41 ######################################################################
  42 
  43 draw_box(){
  44 
  45 #=============#
  46 HORZ="-"
  47 VERT="|"
  48 CORNER_CHAR="+"
  49 
  50 MINARGS=4
  51 E_BADARGS=65
  52 #=============#
  53 
  54 
  55 if [ $# -lt "$MINARGS" ]; then                 # If args are less than 4, exit.
  56     exit $E_BADARGS
  57 fi
  58 
  59 # Looking for non digit chars in arguments.
  60 # Probably it could be done better (exercise for the reader?).
  61 if echo $@ | tr -d [:blank:] | tr -d [:digit:] | grep . &> /dev/null; then
  62    exit $E_BADARGS
  63 fi
  64 
  65 BOX_HEIGHT=`expr $3 - 1`   #  -1 correction needed because angle char "+" is 
  66 BOX_WIDTH=`expr $4 - 1`    #+ a part of both box height and width.
  67 T_ROWS=`tput lines`        #  Define current terminal dimension 
  68 T_COLS=`tput cols`         #+ in rows and columns.
  69          
  70 if [ $1 -lt 1 ] || [ $1 -gt $T_ROWS ]; then    #  Start checking if arguments
  71    exit $E_BADARGS                             #+ are correct.
  72 fi
  73 if [ $2 -lt 1 ] || [ $2 -gt $T_COLS ]; then
  74    exit $E_BADARGS
  75 fi
  76 if [ `expr $1 + $BOX_HEIGHT + 1` -gt $T_ROWS ]; then
  77    exit $E_BADARGS
  78 fi
  79 if [ `expr $2 + $BOX_WIDTH + 1` -gt $T_COLS ]; then
  80    exit $E_BADARGS
  81 fi
  82 if [ $3 -lt 1 ] || [ $4 -lt 1 ]; then
  83    exit $E_BADARGS
  84 fi                                 # End checking arguments.
  85 
  86 plot_char(){                       # Function within a function.
  87    echo -e "\E[${1};${2}H"$3
  88 }
  89 
  90 echo -ne "\E[3${5}m"               # Set box frame color, if defined.
  91 
  92 # start drawing the box
  93 
  94 count=1                                         #  Draw vertical lines using
  95 for (( r=$1; count<=$BOX_HEIGHT; r++)); do      #+ plot_char function.
  96   plot_char $r $2 $VERT
  97   let count=count+1
  98 done 
  99 
 100 count=1
 101 c=`expr $2 + $BOX_WIDTH`
 102 for (( r=$1; count<=$BOX_HEIGHT; r++)); do
 103   plot_char $r $c $VERT
 104   let count=count+1
 105 done 
 106 
 107 count=1                                        #  Draw horizontal lines using
 108 for (( c=$2; count<=$BOX_WIDTH; c++)); do      #+ plot_char function.
 109   plot_char $1 $c $HORZ
 110   let count=count+1
 111 done 
 112 
 113 count=1
 114 r=`expr $1 + $BOX_HEIGHT`
 115 for (( c=$2; count<=$BOX_WIDTH; c++)); do
 116   plot_char $r $c $HORZ
 117   let count=count+1
 118 done 
 119 
 120 plot_char $1 $2 $CORNER_CHAR                   # Draw box angles.
 121 plot_char $1 `expr $2 + $BOX_WIDTH` +
 122 plot_char `expr $1 + $BOX_HEIGHT` $2 +
 123 plot_char `expr $1 + $BOX_HEIGHT` `expr $2 + $BOX_WIDTH` +
 124 
 125 echo -ne "\E[0m"             #  Restore old colors.
 126 
 127 P_ROWS=`expr $T_ROWS - 1`    #  Put the prompt at bottom of the terminal.
 128 
 129 echo -e "\E[${P_ROWS};1H"
 130 }      
 131 
 132 
 133 # Now, let's try drawing a box.
 134 clear                       # Clear the terminal.
 135 R=2      # Row
 136 C=3      # Column
 137 H=10     # Height
 138 W=45     # Width 
 139 col=1    # Color (red)
 140 draw_box $R $C $H $W $col   # Draw the box.
 141 
 142 exit 0
 143 
 144 # Exercise:
 145 # --------
 146 # Add the option of printing text within the drawn box.

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 an aterm).
 bash$ echo -e "\033[4mThis is underlined text.\033[0m"
 	      

Note

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
 
 
 bash$ echo -e '\E[1;33;44m'"BOLD yellow text on blue background"; tput sgr0
 	      

Note

It's usually advisable to set the bold attribute for light-colored foreground text.

The tput sgr0 restores the terminal settings to normal. Omitting this lets all subsequent output from that particular terminal remain blue.

Note

Since tput sgr0 fails to restore terminal settings under certain circumstances, echo -ne \E[0m may be a better choice.

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

ColorForegroundBackground
black3040
red3141
green3242
yellow3343
blue3444
magenta3545
cyan3646
white3747


Example 34-11. Echoing colored text

   1 #!/bin/bash
   2 # color-echo.sh: Echoing text messages in color.
   3 
   4 # Modify this script for your own purposes.
   5 # It's easier than hand-coding color.
   6 
   7 black='\E[30;47m'
   8 red='\E[31;47m'
   9 green='\E[32;47m'
  10 yellow='\E[33;47m'
  11 blue='\E[34;47m'
  12 magenta='\E[35;47m'
  13 cyan='\E[36;47m'
  14 white='\E[37;47m'
  15 
  16 
  17 alias Reset="tput sgr0"      #  Reset text attributes to normal
  18                              #+ without clearing screen.
  19 
  20 
  21 cecho ()                     # Color-echo.
  22                              # Argument $1 = message
  23                              # Argument $2 = color
  24 {
  25 local default_msg="No message passed."
  26                              # Doesn't really need to be a local variable.
  27 
  28 message=${1:-$default_msg}   # Defaults to default message.
  29 color=${2:-$black}           # Defaults to black, if not specified.
  30 
  31   echo -e "$color"
  32   echo "$message"
  33   Reset                      # Reset to normal.
  34 
  35   return
  36 }  
  37 
  38 
  39 # Now, let's try it out.
  40 # ----------------------------------------------------
  41 cecho "Feeling blue..." $blue
  42 cecho "Magenta looks more like purple." $magenta
  43 cecho "Green with envy." $green
  44 cecho "Seeing red?" $red
  45 cecho "Cyan, more familiarly known as aqua." $cyan
  46 cecho "No color passed (defaults to black)."
  47        # Missing $color argument.
  48 cecho "\"Empty\" color passed (defaults to black)." ""
  49        # Empty $color argument.
  50 cecho
  51        # Missing $message and $color arguments.
  52 cecho "" ""
  53        # Empty $message and $color arguments.
  54 # ----------------------------------------------------
  55 
  56 echo
  57 
  58 exit 0
  59 
  60 # Exercises:
  61 # ---------
  62 # 1) Add the "bold" attribute to the 'cecho ()' function.
  63 # 2) Add options for colored backgrounds.

Caution

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.html#color) considerably simplifies using ANSI escape sequences. It substitutes a clean and logical syntax for the clumsy constructs just discussed.

Henry/teikedvl has likewise created a utility (http://scriptechocolor.sourceforge.net/) to simplify creation of colorized scripts.

Notes

[1]

ANSI is, of course, the acronym for the American National Standards Institute.