Linux Console Colors & Other Tricks
By Jay Link


If you've just begun programming on the Linux console, you may find yourself less than enthused about the available color choices (or lack thereof). Indeed, the default -- dreary gray on black -- brings to mind Henry Ford's famous statement regarding color schemes for his Model T: "You can have any color you want, as long as it's black."


You may have noticed that the "ls" command is capable of producing a rainbow of colors; executables are typically green, compressed files are red, and graphics (.GIF, .JPG, etc.) are purple.


But are these special hues limited to file listings? If not, how can you apply the day-glo treatment to your own code?


The answer is surprisingly simple: all you need are some console escape sequences.


Try typing the following at your command prompt:

echo -e "\033[35;1m Shocking \033[0m"

What you should have is the word "Shocking" appearing in bright purple. (Sorry, electric pink is not an option).


This is made possible by \033 , the standard console "escape" code, which is equivalent to ^[ , or 0x1B in hex. When this character is received, the Linux console treats the subsequent characters as a series of commands. These commands can do any number of neat tricks, including changing text colors.


Here's the actual syntax:

\033 [ <command> m

(In practice, you can't have any spaces between the characters; I've just inserted them here for clarity).


Anything following the trailing "m" is considered to be text. It doesn't matter if you leave a space behind the "m" or not.


So this is how you turn your text to a deep forest green:

echo -e "\033[32mRun, forest green, run."

Note that the "-e" argument to "echo" turns on the processing of backslash-escaped characters; without this, you'd just see the full string of text in gray, command characters and all. Finally, the command "0" turns off any colors or otherwise funkified text:

\033[0m

Without the "0" command, your output will continue to be processed, like so:

echo -e "\033[32mThis is green."

echo "And so is this."

echo "And this."

echo -e "\033[0mNow we're back to normal."


Running a command that uses console colors (e.g., ls) will also reset the console to the standard gray on black.



Programming Console Colors

Of course, escape sequences aren't limited to shell scripts and functions. Let's see how the same result can be achieved with C and Perl:

C:
printf("\033[34mThis is blue.\033[0m\n");

Perl:
print "\033[34mThis is blue.\033[0m\n";

Available Colors

Now, how do you know which codes do what? The first eight basic EGA colors are defined as follows:

30 black foreground
31 red foreground
32 green foreground
33 brown foreground
34 blue foreground
35 magenta (purple) foreground
36 cyan (light blue) foreground
37 gray foreground


So, if I wanted the word "ocean" to appear in light blue, I could type the following:

echo -e "The \033[36mocean\033[0m is deep."




Combining Commands

Multiple console codes can be issued simultaneously by using a semicolon (";"). One useful command is "1", which sets text to bold. The actual effect is a lighter shade of the chosen color. So, to get a light magenta (purple) as shown in the first example, you would do this:

echo -e "\033[35;1mCombining console codes\033[0m"

This bolding feature allows you to access the other half of the standard 16 EGA colors. Most notably, brown turns into yellow, and gray turns into bright white. The other six colors are just brighter versions of their base counterparts.


Backgrounds

Text backgrounds can also be set with console codes, allowing you to have white on top of red (for example). Here is the full list of available background options:

40 black background
41 red background
42 green background
43 brown background
44 blue background
45 magenta background
46 cyan background
47 white background


What do you think this does?

echo -e "\033[45;37mGrey on purple.\033[0m"

Finally, here are some other noteworthy command codes:

0 reset all attributes to their defaults
1 set bold
5 set blink
7 set reverse video
22 set normal intensity
25 blink off
27 reverse video off


Conclusion

And now you have the answer to boring, plain ol' console text. A splash of color can liven up almost any display, creating better aesthetics as well as improving the overall feel.

Unfortunately, these techniques are limited to the console, as they don't display over telnet (unless the remote interface is also a Linux console).


Note that the codes given here are known as ECMA-48 compliant. That is, they work on systems other than Linux. (In case you're interested, ECMA is the European Computer Manufacturers Association, a standards body similar to the ISO). Any system with a VT-102 capable console can use the color codes demonstrated above.



Related Resources

1. ECMA This is the page that covers Standard ECMA-48, "Control Functions for Coded Character Sets".

2. "man console_codes" The console_codes man page contains substantial information on not only ECMA-48 compliant codes, but the Linux-specific ones as well.


3. The Linux Documentation Project The LDP is a vast storehouse of Linux-related knowledge.



About Author

Jay Link is twentysomething and lives in Springfield, Illinois. Aside from Linux, his interests include mountain climbing and flying. He administrates InterLink BBS (an unintentionally not-for-profit Internet provider) in his fleeting spare moments, as well as working various odd jobs to pay the rent.

http://www.developer.com/open/article.php/631241

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