Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

In a Bash Prompt (PS1 variable), I'm calling a function to potentially add text to the prompt: export PS1="\u@\h \$(my_function) \$ "

However, the function in the prompt contains ANSI color codes that change based on the output of the function (sometimes red, sometimes green). Adding "\[" to the PS1 variable should escape those codes as non-printing, but if I do an echo in the function, the "\[" get printed literally in the prompt.

How can I escape these ANSI color codes from within a function for use in a bash prompt?

share|improve this question
add comment

2 Answers 2

up vote 16 down vote accepted

The readline library accepts \001 and \002 (ASCII SOH and STX) as non-printable text delimiters. These also work in any application that uses readline.

From lib/readline/display.c:243 in bash source code:

243 /* Current implementation:
244         \001 (^A) start non-visible characters
245         \002 (^B) end non-visible characters
246    all characters except \001 and \002 (following a \001) are copied to
247    the returned string; all characters except those between \001 and
248    \002 are assumed to be `visible'. */

The bash-specific \[ and \] are in fact translated to \001 and \002 at y.tab.c:7640.


Note: If you use bash's printf or echo -e, and if your text has \001 or \002 immediately before a number, you'll hit a bash bug that causes it to eat one digit too many when processing octal escapes – that is, \00142 will be interpreted as octal 014 (followed by ASCII "2"), instead of the correct octal 01 (followed by ASCII "42"). For this reason, use hexadecimal versions \x01 and \x02 instead.

share|improve this answer
    
That does it! echo -e "\001\e[31m\002RED" works as expected. Thanks! –  MidnightLightning Jun 23 '11 at 20:38
add comment

If you want to use them in the prompt, then you do need to do the \[. But if you want to use it in an echo, you have to use \033[.

share|improve this answer
    
Hmmm... Adding \033[ before the ANSI command ("\e[31m") and \033] after it seems to make the next printed character in the prompt not print. –  MidnightLightning Jun 23 '11 at 20:31
1  
You don't want to do \033] after it. \033[31m starts the color, after that you need to set it back with \033[0m –  Wuffers Jun 23 '11 at 20:38
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.