bash shell output color

 

The Bash Shell

Bash is the primary shell of the Linux machine, included here are some tips/tricks with the shell. Use the manual page and learn about PS1, PS2 and PROMPT_COMMAND. The tricks in here can be use in ~/.bash_profile.

Output in Color

Cool terminal output involves color, here is how to set and reset output colors using terminal control characters. To print in color one must first send the control sequences for the color to the terminal, then output the message and reset the terminal, to be nice. One can also create nifty looking prompts with the teniques described here.

Consoloe Color Table

The below key describes all the different sequences that can be sent to change the display format. The disclaimer should be made that "this is how the test computer performed".

Style           Foreground      Background
1st Digit       2nd Digit       3rd Digit
0 - Reset       30 - Black      40 - Black
1 - FG Bright   31 - Red        41 - Red
2 - Unknown     32 - Green      42 - Green
3 - Unknown     33 - Yellow     43 - Yellow
4 - Underline   34 - Blue       44 - Blue
5 - BG Bright   35 - Magenta    45 - Magenta
6 - Unknown     36 - Cyan       46 - Cyan
7 - Reverse     37 - White      47 - White

To instruct echo to interpret these codes you must tell it -en. The -e switch tells echo to interpret your escape sequences and -n tells echo not to make a newline at the end. The activation sequence is \033 this starts the output modification codes. Next is a [ followed by a digits from the above list to represent the style, foreground and background. The sequence is terminated by the letter m. The sequence to get plain red on black would look like this: echo -en "\033[0;31;40m" or once could say echo -en "\033[0;31m" to only affect the foreground. Portions of the sequence can be left out but the digits are still interpreted in the same order. One can switch only the background by saying echo -en "\033[7;43m", this would change the background to yellow without affecting the current foreground settings. Once output is complete the terminal should be reset with echo -e "\033[0m".

Echo in Color Test Script

The code below is a sample of echo in color, it will run through all the sequences and ouput some nice looking tables. This can be use to test what different colors will look like as well as show the hidious combinations.

#/bin/sh
# Show all the colors of the rainbow, should be run under bash
for STYLE in 0 1 2 3 4 5 6 7; do
  for FG in 30 31 32 33 34 35 36 37; do
    for BG in 40 41 42 43 44 45 46 47; do
      CTRL="\033[${STYLE};${FG};${BG}m"
      echo -en "${CTRL}"
      echo -n "${STYLE};${FG};${BG}"
      echo -en "\033[0m"
    done
    echo
  done
  echo
done
# Reset
echo -e "\033[0m"

Setting Terminal Title

( When using a program like PuTTY to access the Linux box sometimes it's nice to have an informative termnal.

Set my title to: hydrogen.edoceo.com
# echo -en "\e]0;hydrogen.edoceo.com\a"

Set my title to: Title
# echo -en "\e]0;Title\a")   

This above dosen't work in my linux . (centos 5.1) I don't know why?

summary

roughly speeking , we can't set the color one time then use all the times. 

ex. echo -en echo -e "\033[0;31m"

and will see the foreground color changed to red. and after executing "ls" or other command which had the output , the termnal color will back to original color.