Diff for "BashFAQ/037"

How can I print text in various colors?

Do not hard-code ANSI color escape sequences in your program! The tput command lets you interact with the terminal database in a sane way:

  # Bourne
  tput setaf 1; echo this is red
  tput setaf 2; echo this is green
  tput bold; echo "boldface (and still green)"
  tput sgr0; echo back to normal

• This will be contentious, but I'm going to disagree and recommend you use hard-coded ANSI escape sequences because terminfo databases in the real world are too often broken. tput setaf literally means "Set ANSI foreground" and shouldn't have any difference with a hard-coded ANSI escape sequence, except that it will actually work with broken terminfo databases so your colors will look correct in a VT with terminal type linux-16color or any terminal type so long as it really is a terminal capable of 16 ANSI colors.

  So do consider setting those variables to hard-coded ANSI sequences such as:

      # Bash
      white=$'\e[0;37m'

  • You assume the entire world of terminals that you will ever use always conforms to one single set of escape sequences. This is a very poor assumption. Maybe I'm showing my age, but in my first job after college, in 1993-1994, I worked with a wide variety of physical terminals (IBM 3151, Wyse 30, NCR something or other, etc.) all in the same work place. They all had different key mappings, different escape sequences, the works. If I were to hard-code a terminal escape sequence as you propose it would only work on ONE of those terminals, and then if I had to login from someone else's office, or from a server console, I'd be screwed. So, for personal use, if this makes you happy, I can't stop you. But the notion of writing a script that uses hard-coded escape sequences and then DISTRIBUTING that for other people should be discarded immediately. - GreyCat
    
    

    • I said it would be contentious, but there is an alternative view. A large number of people today will use Linux on their servers and their desktops and their profiles follow them around. The terminfo for linux-16color is broken. By doing it the "right" way, they will find their colors do not work correctly in a virtual terminal on one of the console pty's. Doing it the "wrong" way will result only in light red becoming bold if they use the real xterm or a close derivitve. If terminfo can't get it right for something as common as linux-16color, it's hard to recommend relying on it. People should be aware that it doesn't work correctly, try it yourself, go through the first 16 colours on A Linux VT with linux-16color. I'd place money on a lot more people using Linux for their servers than any other UNIX based OS and if they are using another UNIX-based or true UNIX they are probably aware of the nuances. A Linux newbie would be very surprised to find after following the "right way" her colors did not work properly on a VT. Of course the correct thing to do is to fix terminfo, but that isn't in my power, although I have reported the bug for linux-16color in particular, how many other bugs are there in it?

tput reads the terminfo database which contains all the escape codes necessary for interacting with your terminal, as defined by the $TERM variable. For more details, see the terminfo(5) man page.

tput sgr0 resets the colors to their default settings. This also turns off boldface (tput bold), underline, etc.

If you want fancy colors in your prompt, consider using something manageable:

  # Bash
  red=$(tput setaf 1)
  green=$(tput setaf 2)
  blue=$(tput setaf 4)
  reset=$(tput sgr0)
  PS1='\[$red\]\u\[$reset\]@\[$green\]\h\[$reset\]:\[$blue\]\w\[$reset\]\$ '

Note that we do not hard-code ANSI color escape sequences. Instead, we store the output of the tput command into variables, which are then used when $PS1 is expanded. Storing the values means we don't have to fork a tput process multiple times every time the prompt is displayed; tput is only invoked 4 times during shell startup. The \[ and \] symbols allow bash to understand which parts of the prompt cause no cursor movement; without them, lines will wrap incorrectly.

See also http://wiki.bash-hackers.org/scripting/terminalcodes for an overview.

CategoryShell